Studies in Mycology. No. 21

22 Dec. 1981

 

Monograph of the genus Pythium

J. VAN DER PLAATS-NITERINK

Centraalbureau voor Schimmelcultures, Baarn

Summary

This revision of the species of Pythium Pringsh. is mainly based on living cultures preserved at the Centraalbureau voor Schimmelcultures. Eighty five species are recognized and described in alphabetical sequence; sixty four of these are available as living strains. In addition, two highly specialized cellulolytic species are treated in an appendix. Pythium buismaniae and P. macrosporum are described as new species. These species and some incompletely known ones are keyed out dichotomously. Seven species are heterothallic and produce sexual organs only in combinations of compatible isolates, whilst others that fail to produce oogonia can generally not be identified at species level. Sixty five taxa are listed as excluded, incompletely known or doubtful.
The species are illustrated by line drawings, a few light micrographs and scanning electron micrographs of omamented oogonia. For each species a compilation of literature data on occurrence and pathogenicity is given, reference being made to 1133 pubfications.

I. Introduction

Butlers (1907), Matthewss (1931), Sideriss (1931, 1931) and Frezzis (1956) treatments of Pythium dealt with limited numbers of species. Middletons work (1943) comprised all the species known at that time. Waterhouse (1967, 1968a) compiled the diagnoses and descriptions of more than 180 species of Pythium and provided a key to 89 recognized species. As several new species were subsequently described, a new monograph was required to cover all present-day knowledge of the genus and to evaluate the available taxonomic criteria. Most of the recognized species are represented by living strains preserved at the Centraalbureau voor Schimmelcultures (CBS).
Pythium species are often pathogenic to many plants and to animals such as fishes or Crustacea. They can cause severe losses in cereals and other crops, as well as ornamental plants. For this reason, condensed data about the geographic distribution and the pathogenicity have been included after the taxonomic treatment of each species. The books by Rangaswami (1962) and Tompkins (1975) proved particularly useful as sourcebooks for the compilation work. In the compilation of literature data concerning each species, no critical judgement of correct identification could be made.

For the sake of convenience, literature given in ecological-phytopathological context is referred to numerically, in taxonomical context with author and year. [p. 2]

II. Material and methods

A thorough study was made of the isolates of Pythium preserved in the CBS collection, which had been obtained from other investigators and institutes or isolated by the author. Many isolates were examined in addition to those in the collection. Cultures were kept at 16C and transferred every 10 weeks on two alternating media, viz. cornmeal agar and potato-carrot agar, as well as being stored on cornmeal agar covered with mineral oil for up to 10 years.
The media used for Petri dish cultures were cornmeal, potato-carrot and hempseed agars, and rarely Schmitthenners (1962b) agar. These media were prepared in the following way:

Cornmeal agar: 60 g freshly ground maize kernels are boiled in 1 l water and allowed to simmer for 1 h. The suspension is then strained through a cloth and filled up with water to 1 1.

Potato-carrot agar: 20 g carrots and 20 g potatoes are chopped and boiled for 10 min in 1 1 water; after filtration through a cloth the liquid is filled up with water to 1 l.

Hempseed agar: 20 g non-denaturated hempseed is washed in distilled water, boiled for 30 min in 1 l distilled water, and filtered through cotton-wool; the liquid is filled up with distilled water to 1 l. The pH should be between 6 and 7.

All media are made up with 15 g agar per litre and autoclaved at 120C for 20 min.

The development of sporangia generally requires water. To induce their formation a small piece of a culture on cornmeal or hempseed agar is placed in a Petri dish in a shallow layer of water, to which a 1-2 cm piece of grass leaf is added. The water used consisted of one part of sterilized pond water and one part of distilled water. The grass leaf was boiled for 10 min. The pond should not be polluted with chemicals or eutrophicated. Changing the water additionally favours the production of sporangia and discharge of zoospores. After a few hours to a number of days, the Pythium colonizes the grass leaf and develops zoosporangia along its margin (Emerson, 1958; Webster and Dennis, 1967; San and Srivastava, 1968).
Oogonia mostly show optimal development on cornmeal agar. The measurements were made on slides in lactophenol-cotton blue. Antheridia often fade away when empty and must be studied in a young stage of development. Maintenance at an appropriate temperature is important, as many species originating from the temperate zones will not produce zoospores above 20C and sometimes only at about 5C. On the other hand, tropical species produce zoospores at 20-30C.

In the case of heterothallic species, crossings were made on cornmeal or potato-carrot agar, or in the case of P. intermedium, on a mixture of equal parts of both media. The compatible partners are inoculated at opposite sides of a Petri dish. Oogonia are formed in a dense zone of contact of the mycelia. The shape of these contact lines is characteristic of the species (Fig. 1). This zone is usually sharply delimited towards the male isolate and more diffuse on the female side.

Fig. l. - Contact lines between compatible colonies of heterothallic species: a. P. sylvaticum (male strain CBS 452.67 left), b. P. heterothallicum (male strain CBS 450.67 left), c. P. catenulatum (CBS 842.68 x 843.68), d. P. intermedium (CBS 221.68 x 267.38), e. P. macrosporum (CBS 574.80 x 575.80), f. P. splendens (CBS 269.69 x 266.69).

Isolates which showed no sexual reproduction are transferred into a Petri dish together with two compatible strains of possibly identical heterothallic species. The reaction on the contact lines of the mycelium with either tester strain gives information about the identity of the isolate. To distinguish oogonial and antheridial strains, transfers of compatible isolates were made to opposite places of a microscope slide covered with a thin layer of a [p. 4] suitable agar medium. These slides were supported on glass rods in a sterile Petri dish containing some sterile water. In certain species the origin of oogonia and antheridia could be traced to the respective strain, in other trials they were complicated or surrounded by mycelium so that male and female strains could not be distinguished, but only an arbitrary designation of + and - strains was made (Campbell and Hendrix, 1967c; Hendrix and Campbell, 1968b, 1969b; Van der Plaats-Niterink, 1968, 1969, 1972).
The temperature relationships are characteristic for the various species. In routine examinations cultures were maintained at room temperature (202C).

Isolation

Most Pythium species are easily isolated by using one of the following methods:
1. Particles of the diseased material or soil or some drops of water are placed in Petri dishes containing 2% water agar (Meredith, 1940). As the Pythium species usually grow more rapidly than other fungi, hyphal tips can be transferred to another medium after 2 or 3 days.
2. The same procedure can be followed using a medium containing an antibiotic substance to suppress the development of bacteria and/or benlate or a polyene antibiotic to suppress the growth of other fungi (see below). This may be especially useful when soil samples are investiged.
3. Small particles of the material are placed in Petri dishes containing water (as described on p. 2) and a few sterilized hemp-seeds. Within a number of days swarming zoospores colonize the hemp-seeds, which are then transferred to a medium containing antibiotics, mostly 415 I U. ml-
penicillin and 50 g ml- streptomycin.
4. One part of a soil sample can be mixed with about 15 parts of sterile sand and moistened. Seeds of corn, hemp or other plants are buried in the soil mixture as baits. After some time they are treated as the hemp-seeds in method 3.
5. Baits consisting of different kinds of fruit (apple, pear, tomato, etc.) can be buried in the soil or in a nylon net placed under water in a ditch, stream, pond etc. After some weeks, depending on the temperature, they are removed and treated as diseased plant material.

Generally basic media were used with the addition of antibiotics to suppress the growth of other fungi and bacteria. Basic media include cornmeal, potato-carrot or Schmitthenners (1962b) synthetic medium. Pimaricin (50-100 g ml-) or benomyl (2 g ml- or more) are particularly helpful to suppress the development or other fungi (Singh and Mitchell, 1961; Eckert and Tsao, 1962; Hine and Luna, 1963; Ocana and Tsao, 1966; Vaartaja, 1968; Van der Plaats-Niterink, 1968, 1975; Tsao and Ocana, 1969; Mircetich and Fogle, 1969; Tsao, 1970; Bollen and Fuchs, 1970; Burr, 1973; Ricci and Messiaen, 1973; Lumsden et al., 1975; Robertson, 1975).
A variety of antibiotics have been used in the course of the years to purify the cultures from bacteria. Combinations of different antibiotics often gave good results: penicillin and streptomycin (Klemmer and Nakano, 1962; Van der Plaats-Niterink, 1968, 1975) or rose bengal in combination with streptomycin, pentachloronitrobenzene (PCNB), penicillin, vancomycin, chlortetracyclin, neomycin or agrimycin (Martin, 1950; Singh and Mitchell, 1961; Kerr, 1963; Vaartaja and Bumbieris, 1964b; Takahashi and Ozaki, 1965; Vaartaja, 1967a; Flowers and Hendrix, 1969; Burr, 1973; Mircetich and Kraft, 1973; Lumsden et al., 1975).
In addition to hemp-seeds, a variety of other materials have been used as baits: leaves [p. 5] (Srinivasan, 1958a; Adair, 1968; Klemmer and Nakano, 1962), small pieces of potato tubers (Hine and Luna, 1963), cockroach wings or dead ants or their pupae (Rajagopalan and Ramakrishnan, 1964), soaked autoclaved sweet corn seeds (Goth et al., 1967), pieces of cucumber disinfected with alcohol (Banihashemi, 1970), or paper discs soaked in culture solutions containing antibiotics (Robertson, 1975). Tsao (1970) gave a survey of the available selective media for isolating plant-pathogenic fungi.
Dilution-plate methods are often used for the quantitative estimation of Pythium inoculum in the soil (Stanghellini and Hancock, 1970; Warcup, 1952; Vaartaja and Bumbieris, 1964b; Vaartaja, 1968; Burr, 1973; Lumsden et al., 1975). A modified soilplate method in which a sieved soil was thoroughly dispersed with molten agar (Buxton and Kendrick, 1963; Tsao and Ocana, 1969) and a soil-particle plate method (Schmitthenner, 1962b; Ricci and Messiaen, 1973) have been used successfully. Bouhot (1975a, b, c) tried to assess the Pythium inoculum potential by counting the diseased cucumber seedlings growing in a test soil.
Sometimes different cardinal temperatures can be used for the selective isolation of a particular species. P. aphanidermatum is best isolated at 38C, but less successfully at 20C, whilst P. ultimum develops best at 20C or below (Lumsden et al., 1975).

III. Morphology and terminology

The mycelium of Pythium species is colourless, sometimes lustrous, occasionally slightly yellowish or greyish lilac. The hyphae are hyaline, the main hyphae are mostly 5-7, occasionally up to 10 m wide. Cross septa are lacking except in old, mostly empty hyphae or where they delimit reproductive organs. Protoplasmatic streaming is often clearly visible in young hyphae. The production of aerial mycelium is more or less dependent on the medium used. On cornmeal and potato-carrot agars most species do not produce aerial mycelium, but on oatmeal agar several species develop profuse aerial mycelium.
Some species (P. sylvaticum, P. ultimum), however, also show a thick cottony mat of mycelium on cornmeal agar. For the evaluation of the mycelial development it is necessary to know the medium on which the fungus has been cultivated. The colonies of some species can be yellowish, due to abundant oospores (P. oligandrum) or hyphal swellings (P. intermedium), those of P. torulosum and some related species are often slightly lilac-coloured.
The various colony patterns are distinctive features. They may consist of acute triangles (Chrysanthemum pattern), obtuse lobes (rosette pattern) or may simply be radiate, with all possible intermediates (see Fig. 2). As the visibility of patterns depends on the transparency of the medium and the temperature, the patterns in the text are described on potato-carrot agar at 25C.

Fig. 2 - Colony patterns (grown on PCA): a. P. mastophorum (CBS 375.72), no special pattern; b. P. anandrum (CBS 285.31), coarsely radiate; c. P. rostratum (CBS 533.74), chrysanthenum pattern; d. P. violae (CBS 159.64), mixed rosette and Chrysanthenum patterns.

The asexual reproduction takes place by means of zoosporangia and zoospores. In Pythium the zoospores are not formed in the sporangium itself but in a vesicle outside it. The sporangium is separated from the rest of the mycelium by a cross wall. At a certain point on the sporangium a discharge tube develops. The undifferentiated content of the sporangium moves through this tube and forms a vesicle at its end. There the [p. 6] zoospores are delimited and start moving. After some time, mostly about 10-20 min., the wall of the vesicle disappears and zoospores swim away in divergent directions.
Zoospores are only liberated under wet conditions. Production of sporangia or hyphal swellings can be stimulated by Mg, K, and Ca ions (Yang and Mitchell, 1965). Exudates of roots and germinating seeds have a stimulatory effect on the germination of sporangia and mycelial growth (Stanghellini and Hancock, 1971b). Germination of encysted zoospores and oospores was stimulated in P. aphanidermatum (Chang-Ho, 1970), germination of sporangia in P. irregulare (Agnihotri and Vaartaja, 1968, 1970) and P. vexans (Biesbrock and Hendrix, 1970a, b), and of oospores in P. mamillatum (Barton, 1957). Experiments have shown that certain sugars and amino acids and especially [p. 7] mixtures of these substances have similar effects (Stanghellini and Hancock, 1971a; Agnihotri and Vaartaja, 1967a, b, 1968, 1970). The same substances cause a positive chemotaxis of the zoospores (Royle and Hickman, 1964). Sterols may also have positive influence on the asexual reproduction (Gmez-Miranda and Leal, 1965). Drechsler (1946a, 1947, 1952a, 1955) observed the transformation of 3-month-old oospores at 10C in P. ultimum and P. butleri into sporangia. Sporangia (hyphal swellings) of P. ultimum and other species are regarded as efficient survival structures in soil (Stanghellini, 1969; Stanghellini and Hancock, 1971a).
The sporangi a can be filamentous or more or less spherical (see Fig. 3). In a number of species the filamentous sporangia cannot or can hardly be distinguished from the rest of the mycelium, unless the vesicle and zoospores indicate the location of the sporangial part. In other species the filamentous sporangia are slightly inflated or form dendroid structures. In P. aphanidermatum and related species the sporangia are strongly inflated, forming lobed or toruloid complexes. Filamentous sporangia often have long discharge tubes, whilst in species with spherical sporangia the discharge tubes are mostly shorter.

Fig. 3. - Sporangia: a. Pythium species, filamentous non-inflated; b. Pythium species, filamentous dendroid; c. P. torulosum, filamentous inflated; d. P. vexons, (sub)globose; e. P. ostracodes, proliferating.

[p. 8]

Fig. 4. - Proliferating sporangia: a. P. dimorphum (CBS 406.72); b. P. undulatum (CBS 157.69) (Nomarski interference contrast, x 750).

Two kinds of spherical sporangia can be distinguished: in a number of species the sporangia proliferate at the bottom and form a new sporangium inside the old sporangial wall (Fig. 4), or the filament grows through the sporangium and the discharge tube and forms a new sporangium outside the old one. In other species proliferation has never been observed.
The zoospores. Much work has been done on zoospores. Waterhouse (1962) and more recently Fuller (1977) have summarized the knowledge about the structure and function of zoospores in the Oomycetes. The zoospores of Pythium are bean- or pearshaped. From a deep lateral groove two flagella emerge. The anterior flagellum consists of an axis with two rows of hairs (mastigonemata) along the entire length (two-sided tinsel type), the posterior consists only of an abruptly ending axis and lacks mastigonemata (whiplash type). The zoospores have a thin wall.
After some time the zoospores loose motility. In P. aphanidermatum the sheath of the flagella takes a chaplet-like form and the axonemata seem to be absorbed into the cytoplasm. The flagella finally disappear. The zoospore rounds off and becomes surrounded by a thicker coat (encystment). An internal rearrangement of the cytoplasmic organization takes place and a cyst wall is formed beneath the cyst coat Later on, a new growing region gives rise to a germ tube (Grove and Bracker, 1968; Colt and Endo, 1972; Kobayashi and Akai, 1974a, b). In a few species of Pythium encysted primary zoospores have been observed to produce secondary zoospores.

The sexual reproduction takes place by means of oogonia and antheridia (see Fig. 5, 6). The female organs, the oogonia, are spherical to limoniform and are intercalary or terminal (Fig. 6d-f, 7). The oogonial wall can be smooth or ornamented [p. 9] with projections. The antheridia, the male organs, consist of an antheridial cell which can be sessile on a hypha, intercalary, or formed terminally on an antheridial stalk. The antheridial cell touches the oogonium and forms a fertilization tube which penetrates the oogonium. Antheridia are termed monoclinous if they originate from the oogonial stalk and diclinous if they originate from a different hypha not closely connected with the one subtending the oogonium. In certain species the proximal part of the oogonial stalk becomes an antheridium which is then called hypogynous. After fertilization the oogonial content forms a zygote, the oospore. Only in rare cases more than one oospore is produced inside an oogonium. The oospore wall is smooth except in P. dictyosporum where oospores are reticulate.

Fig. 5. - Sexual organs: a, P ultimum, smooth oogonia, hypogynous, monoclinous sessile and diclinous antheridia, aplerotic oospores; b. P. paroecandrum, intercalary oogonia, hypogynous and monoclinous sessile antheridia; c. P. oligandrum, ornamented oogonium, no antheridia; d. P. mamillatum, ornamented oogonium, monoclinous antheridium; e. P. sylvatieum, diclinous antheridia with branched stalks; f. P. monospermum, intercalary oogonium, monoclinous and diclinous antheridia, plerotic oospore; g. P. deliense, curyed oogonial stalk, intercalary antheridium, aplerotic oospore.

Though not generally accepted, it seems probable that meiosis takes place only in the oogonium and the antheridium and that the entire thallus is diploid (Sansome, 1963, 1966).

Fig. 6 - Oogonia: a. P. macrosporum (CBS 574.80 x 575.80); b. P. aquatile (CBS 215.80); c. P. oedochilum (CBS 292.37), oogonium with thick-walled oospore; d-f. ornamented oogonia: d. P. uncinulatum (CBS 518.77); e. P. oligandrum (CBS 382.28); f. P. hydnosporum (CBS 253.60); all x 1200.

Fig. 7. - Scanning electron micrographs of ornamented oogonia: a. P. acanthicum (CBS 429.68); b. P. periplocum (CBS 289.31) x 1040; c. P. oligandrum; d. P. anandrum (CBS 285.3i); e. P. mastophorum (CBS 375.72); f. P. uncinulatum (CBS 518.77); a, c -f x c. 1300.

In 1967(c) Campbell and Hendrix showed that heterothallism can occur in Pythium. P. sylvaticum developed numerous sexual organs in dual cultures in the contact zone of two compatible partners. Later other heterothallic species were described (Hendrix and [p. 11] Campbell, 1968b; Van der Plaats-Niterink, 1972) and heterothallism was discovered in already known species (Van der Plaats-Niterink, 1968, 1969; Hendrix and Campbell, 1969b). The lines of contact between compatible strains differ in various species (Fig. 1).
A number of isolates only formed sporangia or hyphal swellings, but did not produce any oogonia in single or dual cultures. Isolates with filamentous non-swollen sporangia were grouped as Group F, isolates with swollen, more or less toruloid sporangia [p. 12] as Group T, isolates with globose, non-proliferating sporangia as Group G, isolates with globose, proliferating sporangia as Group P, and isolates which only made hyphal swellings as Group HS. Exceptions are the named species P. undulatum, P. carolinianum and P. elongatum (Van der Plaats-Niterink, 1975).
The production of oospores is dependent on several factors. The most favourable temperature for sexual reproduction is mostly somewhat lower than that for linear growth, but higher than that for zoosporangial development Some stimulatory effects of Ca, Mg, K, Zn and Mn ions have been mentioned (Yang and Mitchell, 1965; Lenny and Klemmer, 1966; Hsu and Hendrix, 1972).
Important factors for sexual propagation are sterols (chlolestorol, -sitosterol, etc.). Sterols stimulate growth, reproduction (Haskins et al., 1964; Hendrix, 1964, 1965, 1966; Al-Hassan and Fergus, 1969; Child et al., 1969; Brushaber et al., 1972; Pystina, 1973, 1974), increase resistance to high temperatures (Hendrix, 1965; Haskins 1965; Al-Hassan and Fergus, 1969, 1973) and affect the permeability of the cell membranes (Sietsma and Haskins, 1967; Child et al.,1969; Kaosiri and Hendrix,1972; Brushaber et al., 1972). Pythium species do not synthesize sterols. They take them up readily from the medium and metabolize them to esters and compounds more polar than the original sterol (Child et al., 1969; Schlsser et al., 1969; Hendrix et al., 1970; Hendrix, 1975a, b; Dfago and Kern, 1975; Child and Haskins, 1976; McMorris and White, 1977; Gottlieb et al., 1978). In heterothallic species sterols often only stimulate one of the compatible isolates to produce oogoma (Child and Haskins, 1971; Pratt and Mitchell, 1973b). Polyene antibiotics inhibit the sterol induction of oospore formation and increase the permeability of sterol-grown mycelium in Pythium (Folks et al., 1967; Hendrix and Lauder, 1966; Child et al., 1969; Dfago et al., 1969).
The oospores can fill the whole oogonium (plerotic oospores) or leave some space between the oogonial and and oospore wall (a plerotic oospores). The thickness of the oospore wall is characteristic for the species.
After maturation of the oospore, a dormant phase is usually necessary, before germination can take place. At germination, the oospore is converted into a thin-walled structure, which produces a germ tube or acts as sporangium and forms zoospores (De Bary, 1881; Drechsler, 1947, 1952a; Lumsden and Ayers, 1975; Ayers and Lumsden, 1975). The first stage in the germination of oospores is the absorption of the endospore, which is dependent on an exogenous calcium supply. This stage is followed by the formation of a germ tube and depends on the presence of exogenous carbohydrate sources (Stanghellini, 1972; Stanghellini and Russell, 1973). Oospore germination is, moreover, dependent on a high water potential, a suitable pH and temperature (Lumsden and Ayers, 1975; Ayers and Lumsden, 1975; Stanghellini, 1972; Stanghellini and Russell, 1973; Stanghellini and Burr, 1973 a, b). The favourable temperature is mostly about the same as that for vegetative growth. Stimulation of oospore germination was also found with casein (Flowers and Littrell, 1972), light (Schmitthenner, 1972), passage through a snails gut or a treatment with snail enzyme - glucuronidase (Stanghellini and Russell, 1973). Low temperature and lack of nutrients favour oospore germination by means of sporangia and zoospores (Stanghellini and Burr, 1973a; Drechsler, 1946a, 1952a, 1955; Stanghellini, 1973).
The oospores are important survival structures. Oospores in soil were still viable after 8 months to 12 years (Hoppe, 1959, 1966; Drechsler, 1949; Stanghellini and Nigh, 1972; Stanghellini and Russell, 1973; Al-Hassam and Fergus, 1973; Stanghellini, 1974; Lumsden and Ayers, 1975). [p. 13]

Fig. 8. - al-2. Hyphal swellings of P. intermedium; b. chlamydospores of P. tracheiphilum; c. appressoria of P. myriotylum.

In many Pythium species undifferentiated hyphal swellings (see Fig. 8a, b); are formed which can also germinate and form a new thallus. Inmost cases they cannot be distinguished from young spherical sporangia or oogonia. Hyphal swellings may be intercalary or terminal. In P. intermedium terminal chains of hyphal swellings are formed from which the individual cells are easily shed. Thick-walled chlamydospores are rathe rare in this genus but they occur in P. tracheiphilum and P. dimorphum.
Appressoria. In many species of Pythium sickle-, club- or sausage-shaped or subglobose structures of various sizes are formed (Fig. 8c). These appressoria may be single or connected to each other in chains or clusters. On a host plant they can form distal or lateral infection pegs. In cultures the appressoria are attached to the walls of the Petri dishes. Their sizes and shapes are influenced by temperature, pH, carbohydrates, and the N sources. Biotin and inositol were found to stimulate the production of appressoria (Agnihotri, 1969).

IV. Ecology

Pythium species are spread all over the world (791, 1015). Waterhouse and Waterston (1085b) summarized the data about the distribution and pathogenicity of a number of Pythium species. Monographs of ecology and physiology of ten common species were compiled by Domsch et al. (203a). Different species can be found in the tropics and temperate or even cold regions; tropical species have also been recorded from glasshouses in temperate climates. They occur most abundantly in cultivated soils neat the root region in superficial soil layers (743), less commonly in non-cultivated or acid [p. 14] soils where Trichoderma is made responsible for their absence (55). P. graminicola is most abundant at a depth of 7.5-15 cm (507) and P. splendens at 15-30 cm (3). Pythium species have been recorded at depths of 0, 75 and 355 cm, but not in a layer between 120 and 200 cm (347).
Pythium species have also been isolated from soil from arable land, pastures, forests, nurseries, marshes, swamps and water. Dry sandy places, dry forests and salt marshes are generally poor in Pythium species. Apinis (30) isolated ten species from wet pastures, Van der Plaats-Niterink (743) 22 from cultivated soils from Oostelijk Flevoland (Netherlands) and 19 species from meadow soils from the forelands of the river Yssel (Netherlands), whilst soil samples from dry forest in the Netherlands yielded only 0-4 species. The colonization and succession of species in the Zuidelijk Flevoland polder (Netherlands), reclaimed in 1966, were studied during the first six years of its cultivation (743). The number of species per soil sample increased from 0 in 1966 to 13 in 1972; species with filamentous non-inflated sporangia, which generally occur more commonly in open water, dominated during the first years (89% of the isolates in 1968) and decreased to 9% in 1972. In cultivated soil the percentage of species with spherical, nonproliferating sporangia or hyphal swellings was 85-90; the latter group seems to be particularly well adapted to existence in soil. P. rostratum has been recorded from dry soil as well as from water (559, 743).
Pythium species can also be distributed by man or animals. In isolations of fungi from free-living birds in Czechoslovakia and Yugoslavia (432, 433), Pythium species were recovered from nests, intestines and feathers. Other species were recovered from droppings of birds previously fed with these fungi (1006). Earthworms may also play a role in the transport of Pythium spp. (436, 1005).

V. Pathogenicity

Species of Pythium can live saprophytically or parasitically. Their parasitic role often depends on external factors. When conditions are favorable for the fungus but less for the host, Pythium species can become very pathogenic and cause rot of fruit, roots or stems, pre- or post-emergence damping-off of seeds and seedlings. Young or watery tissue is preferentially attacked. Infection takes place when zoospores produce germ tubes (922) or hyphal elements form appressoria and then penetrate the plant by means of infection pegs (657).
The pathogenic capacity is largely determined by the available enzymes. Pectolytic as well as cellulolytic enzymes have been demonstrated in several species. Pectolytic enzymes have been found in P debaryanum (38, 1112) and P. aphanidermatum (150, 453, 1109); cellulolytic activity was shown in several Pythium spp. (66, 719, 720, 721, 722, 725, 988, 1026), in P. mamillatum (193, 496), P. aphanidermatum (1009), P. debaryanum, P. graminicola, P. intermedium, P. irregulare, P. scleroteichum and P. sylvaticum (193).
From a number of Pythium species phytotoxins have been isolated: P. irregulare (608), P. myriotylum (184), P. butleri (452), and P. sylvaticum (77). Indolic growth factors have been isolated from P. sylvaticum (77, 753). [p. 15]
Many species can attack a variety of hosts, others are restricted to one host species (e.g. P. buismaniae). P. oligandrum rarely attacks phanerogams, but is often hyperparasitic on other fungi (see below).
Infection depends on several factors, inoculum density, soil water content, temperature, pH, light intensity, cation content and presence of other micro-organisms. Sufficient amounts or excess of soil water often favour infection and the severity of attack. The influences of temperature are dependent on the species of Pythium involved. The optimum for infection is not always the same as that for growth in pure culture. Infection of cucurbitaceous plants with P. aphanidermatum is most severe between 30 and 35C (1004); P. myriotylum is most pathogenic (pod-rot of penauts) at about 30C, and P. graminicola infects cereals at about 25C (312, 393, 690). Temperatures below 23C are most favorable for infection with P. ultimum, while P. iwayamai (snowblight of cereals) only infects at low temperatures (1004).
Infection mostly takes place on the young roots of phanerogams, but leaves can also be affected. In susceptible plants, root exudates can cause an accumulation of zoospores and accelerate their encystment and germination (1020), especially in differentiating or injured roots (526). Inoculation with hyphal fragments can also cause infection, but at a slower rate (500, 698, 704, 705).
Resistance of plants to Pythium species may be related to the presence of inhibitory phenolic compounds (149, 151), as well as to other substances (524).
Plants are often infected by fungal complexes which may include one or more species of Pythium. Pod-rot of peanuts is caused by a complex of mainly P. myriotylum and Fusarium spp. (282), wilt of peach by P. ultimum as well as F. oxysporum (490). Salt (838) therefore listed Pythium spp. amongst the minor pathogens. Combined infections of host plants with nematodes (Belonolaimus, Meloidogyne, Pratylenchus and Heterodera spp.) and species of Pythium often had greater effects than either of these organisms alone (552, 624, 706, 824, 841, 948, 949, 951, 1098).
Pythium species can play a role in the infection and translocation of viruses in phanerogams (518, 710, 960). Tobacco mosaic virus has been inoculated artificially into Pythium species (95, 708, 1001, 1002) with a resulting growth inhibition.
Pythium species have been isolated from fishes (866), and Daphnia and Bosmina (733, 742, 743), but it is not known whether they are pathogenic to animals. Hyphomyces destruens de Haan & Hoogkamer (which may be a Pythium species) is pathogenic to horses.

VI. Microbial interactions

Interactions are known between species of Pythium and a number of other fungi, actinomycetes, bacteria, animals and viruses. Antagonistic effects of many microorganisms on Pythium spp. have mostly been observed in vitro. Antagonistic effects of actinomycetes have been described against P. aphanidermatum, P. arrhenomanes, P. debaryanum, P. myriotylum, P. splendens, P. ultimum and Pythium sp. (83,180, 203, 330, 463, 510, 538, 579, 805, 1009). Bacteria also often have antagonistic effects demonstrated with P. arrhenomanes (563), P. debaryanum (161, 668, 669) and [p. 16] P. splendens (83). Isolates of Trichoderma spp. often showed antagonism to P. ultimum, P. debaryanum; P. aphanidermatum, P. splendens and Pythium sp. (17, 83, 203, 255, 330, 492, 897, 1114). Rhizoctonia solani can antagonize P. myriotylum (299, 300, 301, 304), P. ultimum (738) and P. aphanidermatum (551). A number of other fungi also inhibit species of Pythium, e.g. species of Aphanomyces, Aspergillus Penicillium, Laetisaria, etc. (396, 397, 462, 477, 492, 505, 506, 572, 573, 1097). Substances have been isolated from soil extracts (1033, 1035, 1036) and the pericarp of Acer saccharum fruits (1086), which are inhibitory to P. ultimum and P. irregulare.
A mutually increased attack has been shown between Fusarium solani and two species of Pythium. P. myriotylum (282, 299, 301) and P. ultimum (738). Culture filtrates of P. irregulare, P. debaryanum and P. ultimum stimulated the growth of Rhizoctonia solani, Aphanomyces euteiches and Thielaviopsis basicola (1118, 1119).
Direct contact of P. acanthicum with Trichoderma spp. or addition of fat-soluble extracts of the Trichoderma mycelium resulted in an increased oogonium production in P. acanthicum which may be ascribed to sterols present in Trichoderma.

Mycoparasitism: Some species of Pythium act as mycoparasites. P. oligandrum, P. acanthicum and P. periplocum are well-known as parasites of P. ultimum, P. debaryanum, P. irregulare, P. mamillatum, P. splendens, P. salpingophorum, P. marsipium, P. buismaniae, P. mastophorum, P. anandrum, P. vexans, P. torulosum, P. gracile and, to a lesser extent, P. butleri, P. graminicola, P. arrhenomanes, P. helicoides, P. oedochilum and P. palingenes (1054, 1055, 1056, 1057, 1058, 1059). Other fungi are, commomly attacked by these three species of Pythium: Phialophora graminicola, Botryotrichum piluliferum, Fusarium roseum, Gaeumannomyces graminis (191, 194) and Pythiogeton autossytus (219). P. oligandrum is an efficient mycoparasite of Rhizoctonia solani, Fusarium culmorum and Trichoderma spp. (191) and may provide a means of biological control of damping-off in sugar beet (1055, 1059, 1060).
Some chytrids can affect Pythium species and are known as oospore parasites (907). Unidentified chytrids as well as species of Leptolegnia, Rhizoctonia, Dactylella, Humicola, Trichothecium, Fusarium, Cephalosporium and Alternaria have been observed as parasites of Pythium spp. (214, personal observations).

VII. The genus Pythium

Pythium Pringsheim - Jb. wiss. Bot. 1: 304. 1858.
Artotrogus Mont. - Gdnrs Chron. 38: 640. 1845.
Cystosiphon Roze & Cornu - Annls Sci. nat., Bot., Sr. 5, 11: 84. 1869.
?Lucidium Lohde - Tagebl. Vers. dt. Naturf. Arzte, Breslau 47: 205. 1874.
Nematosporangium (Fischer) Schrter - Engler & Prantl
, Nat. PflFam. 1: 104. 1897.
Rheosporangium Edson - J. agric. Res. 4: 291. 1915.
Sphaerosporangium Sparrow - Science, N.Y. 73: 42. 1931.

Mycelium well developed, often with appressoria, hyphal swellings, rarely with chlamydospores. Zoosporangia either filamentous, not differentiated from the vegetative hyphae, or consisting of lobate or toruloid inflated elements, or made up of well-defined (sub)globose structures, sometimes internally proliferous. Sporangia terminal, [p. 17] intercalary or laterally sessile, forming a discharge tube of varying length through which the sporangial contents move and form a vesicle at the tip with an undifferentiated mass of protoplasm; this mass then differentiates into a number of biflagellate zoospores. Oogonia (sub)globose, lemon-shaped or ellipsoidal, terminal or intercalary, with a smooth or ornamented wall. Antheridia 0 to several per oogonium, monoclinous, diclinous or hypogynous, stalked or sessile, of various shapes. Oospores usually single, rarely 2-4 in an oogonium, plerotic or aplerotic with a thin or thick (inspissate) wall.
Pythium species occur as saprophytes or parasites in soil, water or on plant or animal substrates.
Type species: Pythium monospermum Pringsheim (lectotype).

The genus Pythium in the present sense was introduced by Pringsheim (1858) but was antedated by Pythium Nees (1823). It was therefore conserved against the latter in 1974, as proposed by Waterhouse (1968b). Montagne (1845) described the congeneric Artotrogus hydnosporus (=Pythium hydnosporum (Mont.) Schrter), so that Artotrogus also has priority over Pythium. A proposal that Artotrogus be rejected has been submitted (Van der Plaats-Niterink, 1981).

Pringsheim based his genus on two fungi which he named P. monospermum and P. entophytum. Zopf (1890) transferred the latter to Lagenidium, so that P. monospermum remained as lectotype species.
Pythium was placed in the Saprolegniaceae by Pringsheim (1858), Cornu (1872), and Berlese and de Toni (1888), and in the Peronosporaceae by de Bary (1881) and Fischer (1892). It is now regarded as type genus of the Pythiaceae Schrter in the Peronosporales.

Notes on synonymous genera

Artotrogus Mont - Montagne (1845) named a single species A. hydnosporus, for which a Latin translation was published by Berkeley (1846). De Bary (1881) mentioned a fungus which he considered to be identical with Montagnes species. Though he was aware that the generic name Artotrogus had priority, he preferred the name Pythium as it had already been allotted several species and because Artotrogus was based on an incomplete and rather confusing description. Atkinson (1895) rejected Pythium Pringsh. because it was antedated by Pythium Nees and made nine new combinations in Artotrogus. However, in 1909 he used Pythium without mention of Artotrogus. Middleton (1943) and Matthews (1931) did not consider the genus Artotrogus. Butler (1907) tentatively included A. hydnosporus in Pythium as P. artotrogus (Mont.) de Bary.

Lucidium Lohde (1874). - This synonymy is considered to be doubtful as the zoospores were said to be formed within the sporangium. Only species: L. pythioides Lohde.

Nematosporangium Schrter - Schrter (1897) erected the family Pythiaceae in which he placed the genera Pythium and Nematosporangium thus raising Fischers subgenus Nematosporangium to generic level. In the latter genus he placed species with filamentous sporangia, in the former those with globose sporangia. This is, however, illegitimate, as the type species of Pythium, P. monosporum, was included in Nematosporangium (ICBN Art. 63). Fritzpatrick (1923), Yachevskij (1931) and [p. 18] Sideris (1931b) followed Schrter and transferred several Pythium species to Nematosporangium.

Rheosporangium Edson (1915) - Only species Rh. aphanidermatum = Pythium aphanidermatum (Coker, 1923; Fitzpatrick, 1923).

Sphaerosporangium Sparrow - Sparrow (1931) proposed that species of Phytophthora and Pythium with globose sporangia be placed in Phytophthora or Sphaerosporangium. Thus Sphaerosporangium is a superfluous name. Sparrow did not designate a type species, nor make any new combinations.

Infrageneric taxa

Fischer (1892) distinguished three subgenera: (1) Aphragmium, species with sporangia not differentiated from the vegetative hyphae and not delimited from them by a septum. Butler (1907) extended this subgenus to include P. monospermum; this was the type species of the genus and hence the subgenus should have been named Pythium (ICBN, Art. 22). Aphragmium was accepted by Schrter (1897) as a subgenus of his genus Nematosporangium. (2) Nematosporangium, species with filamentous sporangia delimited from the vegetative mycelium by a septum. (3) Sphaerosporangium, species with (sub)globose or lemon-shaped sporangia delimited by septa from the vegetative hyphae. This subgenus was divided into two sections: Orthosporangium with sporangia remaining attached to the sporangiophore during zoosporogenesis, and Metasporangium with attached or deciduous sporangia with or without zoospore formation.
Schrter (1897) distinguished two subgenera in his genus Nematosporangium: Eunematosporangium with a delimiting cross wall between the sporangium and the vegetative hyphae, and Aphragmium without delimiting septa. In Pythium two subgenera were distinguished: Eupythium with smooth oogonial walls, and Artotrogus with ornamented oogonial walls.
Petersen (1909) informally distinguished the groups Metasporangium (including P. debaryanum) and Orthosporangium (including P. proliferum de Bary non Schenk and P. undulatum) in addition to the group A phragmium (including P. gracile Schenk), without giving diagnoses or stating that he raised Fischers sections to subgeneric rank.
Sideris (1931b) adopted the genera Nematosporangium and Pythium. He divided Nematosporangium into two sections: Polyandra, with several antheridia, and Oligandra, with few or no antheridia; these sections were subdivided into three and two subsections, respectively. In Pythium sensu Schrter, Sideris (1932) distinguished between two subgenera, Piatyphalla and Stenophalla, based on the shape of the antheridia. These subgenera were then divided into a number of sections and subsections.
Matthews (1931) and Middleton (1943) did not formally distinguish infrageneric taxa, although they used the same distinguishing criteria as the previous authors in their keys and arrangements. [p. 19]

VIII. Key to the species

1

Oogonia produced in single cultures

2

 

Oogonia not or scarcely produced in single cultures

104

 

 

 

2(1)

Oogonial wall ornamented with obtuse or blunt projections

3

 

Oogonial wall smooth or occasionally with few projections

25

Species with ornamented oogonia

3(2)

Oogonia on average 30 m or more diam

4

 

Oogonia on average less than 30 m diam

9

 

 

4(3)

porangia unknown

P. buismaniae

 

Sporangia present

5

 

 

 

5(4)

Sporangia (sub)globose, ellipsoidal or irregular, not proliferating

6

 

Sporangia proliferating

8

6(5)

Oogonia on average 40 m diam or more

P. polymastum

 

Oogonia on average less than 40 m diam

7

 

 

 

7(6)

Antheridial cells mostly single; oogonia on average 38.5 m diam

P. mastophorum

 

Antheridial cells 1-8; oogonia on average 34 m diam

P. uncinulatum

 

 

 

8(5)

Large chlamydospores present

P. dimorphum

 

Chlamydospores absent

P. megalacanthum

 

 

 

9(3)

Sporangia unknown

10

 

Sporangia present

12

 

 

 

10(9)

Oogonial projections less than 3 m long

P. acanthophoron

 

Oogonial projections 3 m or more long

11

 

 

 

11(10)

Oogonial projections acute; antheridia 1(-2), hypogynous

P. hydnosporum

 

Oogonial projections blunt, cylindrical; antheridia 1(-3), usually monoclinous

P. spinosum

see also P. betae

12(9)

Sporangia filamentous

13

 

Sporangia (sub)globose, oval, ellipsoidal or elongated

14

 

 

 

13(12)

Sporangia not inflated; antheridia absent; oogonial projections few, blunt

P. papillatum

 

Sporangia inflated; antheridia present; oogonial projections numerous, blunt

P. periplocum

 

 

 

14(12)

Sporangia not proliferating

15

 

Sporangia proliferating

21

 

 

 

15(14)

Sporangia consisting of irregular complexes of (sub)globose and filamentous elements

16

 

Sporangia single, not forming complexes

17

 

 

 

16(15)

Oogonial projections acute, 5-7(-11) m long

P. oligandrum

see also P. amasculinum

and P. sinense

 

Oogonial projections blunt, 1-2(-5) m long

P. acanthicum

 

 

 

17(15)

Antheridia mostly hypogynous

P. echinulatum

 

Antheridia mostly monoclinous or diclinous

18

[p. 20]

 

 

18(17)

Antheridia usually entwining the oogonial stalk and base

P. helicandrum

 

Antheridia not entwining the oogonial stalk and base

19

 

 

 

19(18)

Oogonial projections blunt, usually cylindrical, irregular, antheridia mostly monoclinous, occasionally diclinous or hypogynous

P. irregulare

see also P. betae

and P. kunmingense

 

Oogonial projections conical, sometimes curved; antheridia mono- or diclinous

20

 

 

 

20(19)

Antheridia monoclinous; oogonial projections conical, blunt

P. mamillatum

 

Antheridia diclinous; oogonial projections mostly acute

P. erinaceus

 

 

 

21(14)

Oogonial projections at maturity blunt, cylindrical, widening or dichotomously branched at the tip

P. polypapillatum

 

Oogonial projections conical or mammifonn

22

 

 

 

22(21)

Antheridia absent

P. anandrum

 

Antheridia 1(-4), monoclinous or diclinous

23

 

 

 

23(22)

Antheridia diclinous, making broad contact with the oogonia; antheridial stalks forming a tangled mass

P. prolatum

 

Antheridia monoclinous or diclinous, making apical contact with the oogonia; antheridial stalks never forming a tangled mass

24

 

 

 

24(23)

Sporangia on average 30 x 25 m

P. paddicum

 

 

 

 

Sporangia on average 87 x 27 m

Phytophthora stellata

Species with smooth-walled oogonia

25(2)

Sporangia filamentous, inflated or not

26

 

Sporangia (sub)globose, proliferating or not, or absent (sometimes only hyphal swellings present)

58

 

 

 

26(25)

Sporangia not or slightly inflated

27

 

Sporangia inflated, forming lobes, diverticles or toruloid structures

43

Sporangia filamentous, non-inflated

27(26)

Oogonia usually only produced in dual cultures (heterothallic species)

107

 

Oogonia commonly produced in single cultures

28

 

 

 

28(27)

Antheridia absent; oogonia smooth or with a few papillae

P. papillatum

 

Antheridia present

29

 

 

 

29(28)

Oospores plerotic

30

 

Oospores aplerotic

32

 

 

 

30(29)

Antheridia single, diclinous; oogonia terminal

P. marinum

 

Antheridia 1-2(-4), mono- and diclinous; oogonia terminal or intercalary

31

 

 

 

31(30)

Antheridia both monoclinous and diclinous; oogonia terminal and intercalary

P. monospermum

 

Antheridia diclinous; oogonia mostly intercalary, rarely terminal; occurring in marine algae

P. porphyrae

 

 

 

32(29)

Oospores reticulate

P. dictyosporum

 

Oospores smooth-walled

33

 

 

 

33(32)

Daily growth rate on cellulosic substrates 0.5-2 mm, no growth on commeal agar

34

 

Daily growth rate 10-20 mm, growing well on common agar media

35

[p. 21]

 

 

34(33)

Colonies peach to flesh coloured; daily growth rate 1.5-2.0 mm

P. fluminum var. fluminum

 

Colonies yellowish; daily growth rate 0.5-1.0 mm

P. fluminum var. flavum

 

 

 

35(33)

Antheridia 1(-2), monoclinous

P. aquatile

 

Antheridia 1-2(-4), at least partly diclinous

36

 

 

 

36(35)

Antheridia diclinous

37

 

Antheridia both mono- and diclinous

38

 

 

 

37(36)

Antheridial cells 1-4 per oogonium, originating from one stalk; rarely more than one antheridial stalk

P. adhaerens

 

Antheridia 1-2 per oogonium on simple unbranched stalks

P. diclinum

see also

P. apleroticum

 

 

 

38(36)

Antheridial stalks unbranched

39

 

Antheridial stalks branched

41

 

 

 

39(38)

Antheridia often sessile

P. dissotocum

 

Antheridia not sessile

40

 

 

 

40(39)

Catenulate hyphal swellings present

P. perniciosum

 

Catenulate hyphal swellings absent

P. tenue

 

 

 

41(38)

Oospore wall 2-4 m thick, pale lilac; oospores yellowish

P .coloratum

 

Oospore wall 1-2 m thick, oospores usually uncoloured

42

 

 

 

42(41)

Antheridial cells large, very variable in size, usually with folds and furrows; oospores on average 14.5 m diam

P. sulcatum

 

Antheridial cells about 8.5 x 5 m, without furrows; oospores on average 18 m diam

P. angustatum

Sporangia filamentous, inflated

43(26)

Oogonia usually only produced in dual cultures (heterothallic species)

108

 

Oogonia commonly produced in single cultures

44

 

 

44(43)

Antheridia absent or rare and then hypogynous

P. dissimile

 

Antheridia present, monoclinous, diclinous or intercalary

45

 

 

 

45(44)

Antheridia often intercalary

46

 

Antheridia usually not intercalary

47

 

 

 

46(45)

Oogonial stalks mostly curved towards the antheridia

P. deliense

 

Oogonial stalks straight

P. aphanidermatum

 

 

 

47(45)

Sporangia consisting of inflated filamentous parts and discrete globose or pyriform elements

P. pyrilobum

 

No discrete globose or pyriform sporangia present

48

 

 

 

48(47)

Oogonia on average about 30 m diam or more

49

 

Oogonia on average less than 25 m diam

52

 

 

 

49(48)

Oospores plerotic or nearly so; up to 15-20 antheridia per oogonium

P. arrhenomanes

 

Oospores aplerotic; less than 10 antheridia per oogonium

50

 

 

 

50(49)

Maximum temperature above 40C

P. myriotylum

 

Maximum temperature below 40C

51

 

 

 

51(50)

Antheridia both mono- and diclinous; daily growth rate 22-25 mm

P. aristosporum

 

Antheridia usually diclinous; daily growth rate 10-16 mm

P. volutum

[p. 22]

 

52(48)

Catenulate hyphal swellings present

P. catenulatum

 

Catenulate hyphal swellings absent

53

 

 

 

53(52)

Sporangia consisting partly of inflated finger-like and partly of undifferentiated mycelial elements; temperature maximum above 40C

P. periilum

 

Sporangia consisting of toruloid inflated elements throughout; temperature maximum below 40C

54

 

 

 

54(53)

Oospores aplerotic

P. indigoferae

 

Oospores plerotic or nearly so

55

 

 

 

55(54)

Antheridia diclinous

P. inflatum

 

Antheridia monoclinous, occasionally diclinous

56

 

 

 

56(55)

Antheridia 1-3(-6); oogonia mostly 21-24 m diam

P. graminicola

 

Antheridia 1-2(-3); oogonia mostly 14-21 m diam

57

 

 

 

57(56)

Antheridia usually originating 1-5 m below the oogonia; oospore wall up to 2 m thick; sporangia consisting of branched inflated elements

P. torulosum

 

Antheridia usually originating 15-25 m below the oogonia; oospore wall 2-4 m thick; sporangia consisting of catenulate complexes of subglobose unbranched outgrowths

P. vanterpoolii

 

 

 

58(25)

Sporangia (sub)globose, proliferating or not

59

 

Sporangia never observed

93

 

 

 

59(58)

Sporangia not proliferating

60

 

Sporangia proliferating

81

Sporangia (sub)globose, non-proliferating

60(59)

Oogonia usually only produced in dual cultures (heterothallic species)

110

 

Oogonia produced in single cultures

61

 

 

 

61(60)

Oospores reticulate

P. pythioides

 

Oospores smooth-walled

62

 

 

 

62(61)

Sporangia large (up to 130 m long), transversely attached to the subtending hyphae, papillate

P. grandisporangium

 

Sporangia usually less than 50 m long

63

 

 

 

63(62)

Sporangia consisting of both globose or pyriform elements and inflated filamentous parts

P. pyrilobum

 

Sporangia consisting only of (sub)globose elements

64

 

 

 

64(63)

Oospores plerotic or nearly so

65

 

Oospores definitely aplerotic

70

 

 

 

65(64)

Antheridia typically hypogynous

 

P. hypogynum

see also P. acrogynum

 

Antheridia mono- or diclinous, occasionally hypogynous or absent

66

 

 

 

66(65)

Antheridia monoclinous, often sessile or hypogynous; oogonia usually intercalary, occasionally terminal

P. rostratum

 

Antheridia never hypogynous, occasionally absent; oogonia terminal or intercalary

67

 

 

 

67(66)

Oogonia usually intercalary, often catenulate, occasionally terminal; antheridia often absent

P. salpingophorum

 

Oogonia usually terminal, occasionally intercalary

68

 

 

 

68(67)

Temperature maximum above 40C

P. orthogonon

 

Temperature maximum below 40C

69

[p. 23]

 

 

69(68)

Oospore wall up to 3 m thick; thick-walled chlamydospores sometimes present

P. tracheiphilum

 

Oospore wall less than 1.5 m thick; chlamydospores absent

P. salinum

 

 

 

70(64)

Antheridia monoclinous, bell-shaped or lobed

71

 

Antheridia neither bell-shaped nor lobed

72

 

 

 

71(70)

Antheridia typically bell-shaped, not lobed; oospores on average 21 m diam

P. perplexum

 

Antheridia bell-shaped and lobed; sporangia occasionally proliferating; oospores on average 17 m diam

P. vexans

 

 

 

72(70)

Sporangia often over 40 m long

73

 

Sporangia less than 40 m long

75

 

 

 

73(72)

Antheridia hypogynous, occasionally mono- or diclinous

P. pulchrum

 

 

 

74(73)

Oogonia often irregularly shaped, terminal; chlamydospores absent

P. jirovecii

 

Oogonia globose, intercalary; thick-walled chlamydospores present

P. iwayamai

 

 

 

75(72)

Antheridia large, irregular, making broad lengthwise contact with the oogonia near the stalk

P. chamaehyphon

 

Antheridia small, stalked or sessile, making apical contact with the oogonia

76

 

 

 

76(75)

Oogonia intercalary or terminal; oospore wall 1.0-1.5 m thick

77

 

Oogonia usually terminal; oospore wall 2 m or more thick

78

 

 

 

77(76)

Oogonia sometimes catenulate, without projections

P. paroecandrum

 

Oogonia never catenulate, occasionally with blunt, irregular projections

P. irregulare

 

 

 

78(76)

Antheridia diclinous

P. macrosporum

 

Antheridia monoclinous, rarely diclinous

79

 

 

 

79(78)

Antheridial stalks often swollen, originating at a distance of 5-15 m below the oogonia

P. okanoganense

 

Antheridial stalks never swollen, originating immediately below the oogonia

80

 

 

 

80(79)

Sporangia and zoospores produced at room temperature

P. ultimum var. sporangiiferum

 

Sporangia and zoospores not produced at room temperature, hyphal swellings germinating with germ tubes only

 

P. ultimum var. ultimum

Sporangia proliferating

81(59)

Oogonia not produced in single cultures

111

 

Oogonia commonly produced in single cultures

82

 

 

 

82(81)

Oogonia often containing two or more oospores

P. multisporum

 

Oogania containing a single oospore

83

 

 

 

83(82)

Oogonia on average 30 m diam or more

84

 

Oogonia on average less than 30 m diam

89

 

 

 

84(83)

Antheridia making broad apical contact with the oogonia

P. marsipium

 

Antheridia applied lengthwise to the oogonia

85

 

 

 

85(84)

Oospores plerotic or nearly so; antheridia usually monoclinous

P. ostracodes

 

Oospores aplerotic; antheridia usually diclinous

86

[p. 24]

 

 

86(85)

Antheridia long cylindrical, without waves or furrows; oospore wall 4-6 m thick

P. helicoides

 

Antheridia wavy or furrowed; oospore wall up to 3.5 m thick

87

 

 

 

87(86)

Oogonia usually terminal, rarely intercalary

P. oedochilum

 

Oogonia terminal, intercalary or laterally sessile

88

 

 

 

88(87)

Sporangia subglobose or ovoid, terminal on long unbranched hyphae, sometimes in sympodial succession arising from immediately below a sporangium; antheridial stalks often enwrapping the oogonial stalk

P. palingenes

 

Sporangia (sub)globose, terminal, intercalary or laterally sessile; antheridial stalks rarely enwrapping the oogonial stalks

P. polytylum

 

 

 

89(83)

Oospores plerotic; oogonia mostly intercalary, often catenulate

P. salpingophorum

 

Oospores aplerotic

90

 

 

 

90(89)

Oogonia usually intercalary, occasionally terminal

P. middletonii

 

Oogonia usually terminal, rarely intercalary

91

 

 

 

91(90)

Antheridia bell-shaped or lobed

P. vexans

 

Antheridia globose or clavate

92

 

 

 

92(91)

Oospore wall less than 1 m thick; oospores 12-19 m diam

P. nagaii

 

Oospore wall up to 3 m thick; oospores 22-27 m diam

P. okanoganense

Sporangia and zoospores unknown

93(58)

Oogonia produced usually only in dual cultures (heterothallic species)

113

 

Oogonia produced in single cultures

94

 

 

 

94(93)

Colonies on cellulosic subtrates saffron to pale yellow; no growth on commeal agar

P. uladhum

 

Colonies white or colourless; growing well on cornmeal agar

95

 

 

 

95(94)

Antheridia often sessile

96

 

Antheridia usually stalked

97

 

 

 

 

 

 

96(95)

Oogonia on average about 21 m diam; antheridial stalks not branched

P. ultimum var. ultimum

 

Oogonia on average about 29 m diam; antheridial stalks sometimes branched

P. violae

 

 

 

97(95)

Oospores plerotic

98

 

Oospores aplerotic

100

 

 

 

98(97)

Oogonia on average 30 m diam or more

P. hemmianum

 

Oogonia on average less than 30 m diam

99

 

 

 

99(98)

Antheridia monoclinous

P. connatum

 

Antheridia both mono- and diclinous

P. pleroticum

 

 

 

100(97)

Globose hyphal swellings absent

101

 

Globose hyphal swellings present

102

 

 

 

101(100)

Filamentous inflated hyphal swellings present; antheridial stalks not coiling around the oogonia

P. tardicrescens

 

Filamentous inflated hyphal swellings absent; antheridial stalks entangling the oogonia

P. scleroteichum

 

 

 

102(100)

Hyphal swellings large, often 30-40 m diam

P. splendens

 

Hyphal swellings, if present, on average less than 30 m diam

103

[p. 25]

 

 

103(102)

Aerial mycelium on commeal agar profusely cottony; daily growth rate at 25C 30 mm

P. sylvaticum

 

Some aerial mycelium on commeal agar, daily growth rate at 25C 20 mm

P. heterothallicum

Heterothallic species and species without oogonia

(identification to be verified with standard mating partners)

104(1)

Sporangia present

105

 

Sporangia not formed, hyphal swellings often present

113

 

 

 

105(104)

Sporangia filamentous, inflated or not

106

 

Sporangia globose, proliferating or not

109

 

 

 

106(105)

Sporangia filamentous, non-inflated

107

 

Sporangia filamentous, inflated

108

 

 

 

107(27, 106)

Oogonia formed in dual cultures; daily growth rate 7-10 mm; colonies on potato-carrot agar with a Chrysanthemum pattern

P. flevoense

 

Oogonia not formed in dual cultures

Pythium group F

 

 

 

108(43, 106)

Oogonia formed in dual cultures; catenulate hyphal swellings present

P. catenulatum

 

Oogonia not formed in dual cultures

Pythium group T

 

 

 

109(105)

Sporangia globose to elongate, non-proliferating

110

 

Sporangia globose to elongate, proliferating

111

 

 

110(60, 109)

Oogonia formed in dual cultures; hyphal swellings absent

P. macrosporum

 

Oogonia not formed in dual cultures; hyphal swellings present or absent

Pythium group G

see also P. elongatum

 

 

 

111(81, 109)

Sporangia large, up to more than 100 m long; thick-walled chlamydospores present

P.undulatum

 

Sporangia smaller (20-30 m diam)

112

 

 

 

112(111)

Catenulate hyphal swellings present

P. carolinianum

 

Catenulate hyphal swellings absent

Pythium group P

 

 

 

113(93, 104)

Hyphal swellings large, often 30-40 m diam; oogonia formed in dual cultures

P. splendens

 

Hyphal swellings, if present, on average less than 30 m diam

114

 

 

 

114(113)

Deciduous catenulate hyphal swellings present; oogonia formed in dual cultures

P. intermedium

 

Hyphal swellings not catenulate

115

 

 

 

115(114)

Oogonia formed in dual cultures

116

 

Oogonia not formed in dual cultures

Pythium group HS

 

 

 

116(115)

Aerial mycelium on cornmeal agar profusely cottony; daily growth rate at 25C 30 mm

P. sylvaticum

 

Some aerial mycelium on commeal agar, daily growth rate at 25 C 20 mm

P. heterothallicum

[p. 26]

 

 

IX. Descriptions of the recognized species

1. Pythium acanthicum Drechsler - Fig. 9, 7a.

Pythium acanthicum Drechsler - J. Wash. Acad. Sci 20: 408-409. 1930.

Fig. 9. P. acanthicum, CBS 284.31. a1-5. oogonia and antheridia, b1-3. sporangia with discharge tubes.

Colonies on cornmeal agar submerged, becoming yellowish after some time, on potato-carrot agar showing a rosette pattern. Main hyphae up to 5 m wide. Sporangia intercalary and occasionally terminal, subglobose, but often forming complexes of two or more intercalary, subglobose or irregular portions connected by hyphal pieces. Discharge [p. 27] tubes (10-)20(-200) m long; zoospores formed at 20C, 15-20 in a vesicle, encysted 8-10 m diam. Oogonia terminal or intercalary, globose, (17-)21-24(-27) (av. 22) m diam, wall thin and ornamented; projections conical, with a blunt tip, (1-)2.2-3.0(-5) m long. Antheridia 1(-2) per oogonium, typically monoclinous, rarely diclinous, soon vanishing after fertilization; antheridial stalk originating at distances up to 25 m below the oogonium, possessing often branched vegetative prolongations; antheridial cells inflated clavate, straight or crook-necked, often with one or two constrictions, applied to the oogonium with the tip or broadly with the entire cell. Oospores plerotic or nearly so, but always free from the oogonial wall, colourless or slightly yellow, (16-)18-23(-25) (av. 21) m diam, wall 1-2.8 m thick.
Cardinal temperatures: minimum 5C, optimum 25-30C, maximum 38C. Daily growth rate on cornmeal agar at 25C: 25 mm or more.
Description based on CBS 284.31.

Material examined

CBS 284.31, type culture, isolated from Citrullus vulgari, USA, Ch. Drechsler, comm. S. F. Ashby. CBS 377.34, isolated from Solanum tuberosum, Sweden, B. T. Palm, 1934. CBS 429.68 and 430.68, isolated from soil near a pond in Bilthoven and garden soil in Utrecht, respectively, Netherlands, A. J. P.-N., 1965. CBS 431.68, isolated from ditch water, near Egmond, Netherlands, M. Kutkov, 1967. CBS 432.68, 433.68 and 434.68, isolated from soil near a ditch in Oostelijk Flevoland, garden soil, Bolsward, and soil near Rhenen, respectively, Netherlands, A. J. P.-N., 1965 and 1966. IMI 102377 and 62019, (slides) and several other isolates not maintained in the CBS collection.

 

 

Discussion

P. acanthicum differs from most other species with ornamented oogonia by its swollen but contiguous sporangia which are connected by hyphal elements. Only P. oligandrum also has contiguous sporangia but differs from P. acanthicum by its longer and more pointed oogonial spines, its more aplerotic oospores and its often parthenogenetic development of the oospores. Moreover, when antheridia are present in P. oligandrum, they are mostly diclinous, whilst in P. acanthicum they are mostly monoclinous. P. acanthicum differs from P. mamillatum by its sporangia, larger oospores and different shape of the oogonial spines, which are often curved in P. mamillatum.

Occurrence and pathogenicity

P. acanthicum has been recorded from Citrullus vulgaris in the USA (211, 215, 782), Argentina (291), Queensland (991), and the USSR (765), Dahlia sp., Pisum sativum, Phaseolus vulgaris, Solanum melongena and Curcuma domestica in South Africa (1066), the USA (643), Czechoslovakia (145), the USSR (765) and Saba (556), vegetables in New Zealand (817, 819) and Queensland (991), sugar cane in Japan (1077), woody plants such as Pinus sp., Carya illinoensis, Camellia sp., Azalea and Rosa spp. in the USA (363, 364) and Tanzania (234), Cryptomeria japonica, Juniperus chinensis, Setcreasea sp. and Hebe sp. in New Zealand (816), and soil in England (30, 1074), the USA (126, 368), New Zealand (816), Australia (754), Micronesia (1), and the Netherlands (743).

According to Drechsler (215), P. acanthicum can cause blossom-end-rot and fruit-rot of water melon. Robertson (817) found it to be highly pathogenic to tomato seedlings, but only weakly parasitic to a number of other plants. He suggested that various strains of the species might vary in their pathogenicity. It was not pathogenic to maize seedlings (409) nor to Sitka spruce seedlings (1074). [p. 28]

 

Fig. 10.- P. acanthophoron. a two stages of oogonial development (redrawn from Sideris, 1932; magnification not indicated).

2. Pythium acanthophoron Sideris - Fig. 10.

Pythium acanthophoron Sideris - Mycologia 24: 36. 1932.

Colonies on cornmeal agar submerged, on potato-carrot agar submerged with a vaguely radiate pattern. Main hyphae up to 7 m wide, irregular in width, slightly dendroid, with short side-branches. Sporangia not observed. Oogonia globose, ornamented, 20-30 m diam, often abortive; ornamentation 2.5 m long. Antheridia of monoclinous or diclinous origin; antheridial cells bag-like, vermiform or allantoid, 10-20 x 4-8 m, with a slight constriction in the middle, making broad contact with the oogonium. Oospores globose, 15-20 m diam, with a 1.5 m thick wall.
Cardinal temperatures: minimum 5C, optimum 30C, maximum below 37C. Daily growth rate on potato-carrot agar at 25C: 20 mm.
Description based on Sideriss diagnosis, Waterhouse (1967) and CBS 337.29.

Material examined

CBS 339.27, isolated from Ananas sativus, Hawaii, C. P. Sideris, 1929.

Discussion

The isolate CBS 339.27 shows neither sporangia nor sexual reproduction. Sideriss description is rather poor and confusing. From the pictures and according to Waterhouse (1967), the ornamentations seem to be conical and rather blunt. One or possibly two antheridia may be present, making broad contact with the oogonium. It is not clear whether the oospore is plerotic or aplerotic.

Occurrence and pathogenicity

P. acanthophoron was originally isolated from diseased leaves of Ananas sativus in Hawaii. It has also been recorded from soil in the Philippines (765a). According to Sideris (889), the fungus is only weakly pathogenic to Ananas. [p. 29]

 

Fig. 11. - P. adhaerens. a1-3 oogonia and antheridia, b. zoospore discharge from sporangium in Rhizoclonium, c. zoospores, d. appressoria, d3. attached to algal cell (from Sparrow, 1931).

 

3. Pythium adhaerens Sparrow - Fig. 11.

Pythium adhaerens Sparrow - Ann. Bot. 45: 272. 1931.

Colonies on cornmeal agar submerged, on potato-carrot agar without a special pattern. Main hyphae up to 7 m wide. Appressoria clavate, varying in size, usually 12 x 7 m. Sporangia filamentous, not differentiated from the vegetative hyphae. Encysted zoospores 5-9 m diam. Oogonia smooth, globose, terminal or intercalary, 11-25 m [p. 30] (av. 17.5 m) diam. Antheridia 1-4 per oogonium, borne on a single stalk or rarely on distinct stalks, diclinous, often encircling the oogonium; antheridial cells crook-necked, 15 x 7 m. Oospores aplerotic, 7-22 m (av. 14.5 m) diam, wall 2-2.5 m thick.

No material available.

Discussion

P., adhaerens forms extramatrical, strictly filamentous sporangia. According to Sparrow (1931b), intercommunicating clumps of (sub)globose intramatrical appressoria also occurred in the Rhizoclonium host; these were connected with a hypha which penetrated the host cell-wall and functioned as a discharge tube. The contents of the whole complex and concomitant hyphae were discharged and formed zoospores. However, these structures were never found in pure cultures.

P. adhaerens is close to P. angustatum, but differs from this and other species with strictly filamentous sporangia by its antheridial structures, which consist of 1-4 antheridial cells borne on a single diclinous stalk.

Occurrence and pathogenicity

P. adhaerens was originally isolated from Rhizoclonium hieroglyphicum in the USA. Another report is known from sugar cane in Malaysia (554). According to Sparrow (917), P. adhaerens is pathogenic to various algae, may cause damping-off of sugar-beet seedlings and root rot of maize and pea, and infect fruits of tomato and cucumber.

 

4. Pythium anandrum Drechsler - Fig. 12, 2b, 7d.

Pythium anandrum Drechsler - J. Wash. Acad. Sci. 20: 410-411. 1930; Phytopathology 29: 415-420. 1939, and 36: 838-846. 1946.

Colonies on cornmeal agar submerged or with scanty aerial mycelium, on potatocarrot agar forming a radiate pattern (Fig. 2b). Main hyphae up to 8.3 m wide. Sporangia terminal on simple or sparingly branched hyphae, ellipsoidal or elongate, (32-) 54-86(-96) x (15-)25-38(-40) m (av. 62 x 28 m), usually papillate, occasionally proliferating. Zoospores formed at 18C, discharge tubes 0-10 m long; encysted zoospores 12-14 m diam. Oogonia terminal, (sub-)globose, (12-)27-29(-33) m (av. 28 m) diam, ornamented with conical spines, 3-11 m long and 2-4 m diam at the base. Antheridia normally lacking. Oospores developing parthenogenetically, plerotic or nearly so, (11-)21-27(-28) m (av. 24.5 m) diam, wall up to 1.8(-2.1) m thick.

Cardinal temperatures: minimum under 5C, optimum 28C, maximum about 31C. Daily growth rate on cornmeal agar at 25C: 25 mm.

Description based on CBS 258.31. [p. 31]

Fig. 12. - P. anandrum, CBS 285.31. a-. oogonia, b-7. sporangia, some proliferating. [p. 32]

Material examined

CBS 258.31, type culture, isolated from Rheum rhaponticum, USA, C. Drechsler, comm. T. S. F Ashby in 1931. CBS 394.61, isolated from Rhododendron sp., comm. Plant Protection Service, Wageningen, 1960 (antheridial isolate).

Discussion

The proliferating, papillate sporangia and the conspicuously ornamented oogonia are characteristic. Among the species with ornamented oogonia, only P. anandrum, P. megalacanthum and P. prolatum form proliferating sporangia. The sporangia of P. megalacanthum are non-papillate, in P. prolatum antheridia are always present and the ornamented oogonial wall forms a very thick covering, unlike that in P. anandrum. Antheridia are also often lacking in P. oligandrum, but in this species the oogonial spines are more slender than in P. anandrum, while the sporangia of P. oligandrum consist of complexes of spherical units. Drechsler also described an occasional occurrence of oogonia with two oospores, which also occur in some other species, e.g. P. multisporum and P. violae. In P. anandrum sporangia sometimes develop from old oospores. These sporangia never proliferate and secondary sporangia are only produced by terminal sporangia. Occasionally small oogonia are formed which bear only traces of ornamentation or no ornamentation at all.

According to Waterhouse (1967), P. anandrum sometimes shows antheridia 12 x 6 m which can be irregular but do not entwine the oogonial stalk. She considered CBS 394.61 as an antheridial isolate of P. anandrum (pers. comm.).

Occurrence and pathogenicity

P. anandrum has been reported from the USA from a small number of plants, viz. fruits of Citrullus vulgaris (215) and Cucumis sativus, and roots of Phaseolus vulgaris, Rheum rhaponticum (211) and Spinacia oleracea (643, 644). Hickman (386) reported it from Fragaria sp. in Scotland. Robertson (816) isolated it from container-grown plants in New Zealand and found it to be mildly pathogenic to tomato seedlings. It has also been isolated from soil of pine plantations in S. Australia (190) and from soil and avocado in California (354, 355, 356). P. anandrum is possibly involved in crown rot of rhubarb (211, 644). Pathogenicity tests on cucumber fruits and seedlings (219) resulted in fruit-rot and damping-off.

 

5. Pythium angustatum Sparrow - Fig. 13.

Pythium angustatum Sparrow - Ann. Bot. 45: 272. 1931.

Colonies on cornmeal agar submerged, on potato-carrot agar with a Chrysanthemum pattern. Main hyphae up to 4 m wide. Sporangia strictly filamentous, not inflated. Encysted zoospores 6 m diam. Oogonia terminal or intercalary, (sub)globose or rarely sac-like, 13-27 m (av. 20 m) diam. Antheridial cells 1-5 per oogonium, borne on one to several stalks of diclinous or monoclinous origin. Antheridial cells 8.5 x 5 m, making broad apical contact with the oogonium. Oospores usually single, occasionally 2-4 per [p. 34] oogonium, aplerotic, 11-25 (av. 18) m diam, wall 1-1.8 m thick.

 

 

 

 

Fig. 13. - P. angustatum. a1-5. oogonia and antheridia, b1-3. filamentous sporangia and discharge of zoospores, in b Protruding from spirogyra cell, c1-2, active and encysted zoospores; b, c at lower magnification (bottom bar) (from Sparrow, 1931).

 

Cardinal temperatures: minimum 5C, optimum 25C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 9 mm.

Description based on CBS 522.74 and Sparrows diagnosis.

Material examined

CBS 522.74, isolated from soil in Oostelijk Flevoland, Netherlands, A. J. P.-N., 1971.

Discussion

P. angustatum is close to species such as P. adhaerens, P. tenue, etc., which all have filamentous non-inflated sporangia. Its aplerotic oospores and characteristic antheridial structures distinguish it from P. monospermum and P. marinum, the thinner oospore walls and the presence of monoclinous antheridia from P. adhaerens and P. diclinum, and the larger oogonia from P. tenue.

Occurrence and pathogenicity

P. angustatum was originally isolated from Spirogyra crassa in the USA. It has also been recorded from water in the USSR (559, 634) and strawberry in Japan (1081).

The species was found to be a parasite of Spirogyra crassa and was able to infect 3 out of 13 other species of algae. It was not found to be pathogenic to a variety of phanerogams, with the exception of maize in which it caused a root-rot under certain environmental conditions (917).

 

6. Pythium aphanidermatum (Edson) Fitzp. - Fig. 14.

Rheosporangium aphanidermatum Edson - J. agric. Res. 4: 291. 1915 = Pythium aphanidermatum (Edson) Fitzp. - Mycologia 15:168. 1923 = Nematosporangium aphanidermatum (Edson) Fitzp. - Mycologia 15: 168. 1923 = Nematosporangium aphanidermatum (Edson) Jacz. - Opredelitel Gribov, p. 97. 1931.

Pythium butleri Subramaniam - Mem. Dep. Agric. India, Bot. 10: 193. 1919.

Nematosporangium aphanidermatum var. hawaiiense Sideris - Mycologia 23: 286. 1931.

Colonies on cornmeal agar with cottony aerial mycelium, on potato-carrot agar with some loose aerial mycelium without a special pattern. Main hyphae up to 10 m wide. Sporangia consisting of terminal complexes of swollen hyphal branches of varying length and up to 20 m wide. Zoospores formed at 25-30C. Encysted zoospores 12 m diam. Oogonia terminal, globose, smooth, (20-) 22-24(-25) m (av. 23 m) diam. Antheridia mostly intercalary, sometimes terminal, broadly sac-shaped, 10-14 m long and 10-14 m wide, 1(-2) per oogonium, monoclinous or diclinous; oospores aplerotic, (18-)20-22 m (av. 20.2 m) diam, wall 1-2 m thick.

Cardinal temperatures: minimum 10C, optimum 35-40C, maximum over 40C. Daily growth rate on potato-carrot agar at 25C: over 30 mm.

Description based on CBS 118.80, which is here proposed as neotype. [p. 35]

Fig. 14. - P. aphanidermatum, CBS 118.80. a1-2. oogonia and antheridia, b1-3. toruloid sporangia, lower magnification, c. appressoria.

 

Material examined

CBS 258.30, isolated from Carica papaya, Hawaii, C. P. Sideris, 1930; received as Nematosporangium aphanidermatum var. hawaiense. CBS 313.33, isolated from Nicotiana tabacum, Sumatra, A. Meurs, 1932. CBS 216.46, isolated from Cucumis sativus, England, C. J. Hickman, 1946. CBS 339.49, isolated from Hibiscus sp. seedling, K. B. Boedijn and J. Reitsma, 1948. CBS 164.68 = IMI 120404, isolated from muck soil, USA, comm. G. M. Waterhouse. CBS 634.70, isolated from Lycopersicon esculentum, Israel, Z. R Frank, 1970. CBS 188.80, neotype culture, comm. E. Laville, Paris, in 1968.

Discussion

P. aphanidermatum was first described as Rheosporangium aphanidermatum by Edson (1915), who thus established a new genus of the Saprolegniaceae. Carpenter (1928), working with fungi associated with sugar cane root-rot, noted a close agreement between his isolates, P. aphanidermatum and P. butleri. Coker (1923) placed Rheosporangium in synonymy with Pythium. Fitzpatrick (1923) concluded that the new combination Pythium aphanidermatum should be preferred above Edsons binomial, unless the genus Nematosporangium (A. Fischer) Schrt. was recognized, in which case the fungus should be called Nematosporangium aphanidermatum. He already considered P. butleri as synonymous with P. aphanidermatum.

P. aphanidermatum belongs to a group of species characterized by the possession of inflated filamentous sporangia, often intercalary antheridia and aplerotic oospores. P. deliense and P. indigoferae also belong to this group. P. deliense and P. indigoferae differ from P. aphanidermatum by their oogonial stalks which curve towards the antheridia and smaller oogonia. [p. 36]

P. butleri is not different from P. aphanidermatum. Drechsler (1934, 1960) regarded these two species as different, though closely related. According to Drechsler, P. butleri is more robust than P. aphanidermatum and has larger oogonia. Edsons isolate produced oogonia ranging from 22-27 m, while Subramaniams isolate had oogonia ranging from 18-33 m. In the extensive literature on P. aphanidermatum the average sizes of the oogonia vary from 21 m (Malik, 1945) to 27 m (Ravis and Boccas, 1969) and of the oospores from 17 m (Malik, 1945) to 22.1 m (Hickman, 1944). All sizes between these have been recorded. The author compared a number of isolates labelled P. aphanidermatum or P. butleri and also found the size range of the oogonia to vary from 22 to 30 m and that of the oospores from 20 to 25 m. As all intermediate sizes were also present in the available material and in the literature data, it does not seem to be possible to distinguish P. aphanidermatum from P. butleri. Krywienczyk and Dorworth (1980) investigated the serological relationships of a number of Pythium species and found P. aphanidermatum and P. butleri identical but different from the other investigated species.

Occurrence and pathogenicity

P. aphanidermatum is a typical plant parasite of warm regions. Its overall distribution is shown on the CMI Map No. 309, 1955. It has been isolated in the USA from alfalfa (856), Beta sp. (237, 527, 616, 639, 643, 1008, 1124, 1126), Brassica sp. (206), Carica papaya (476, 643, 728, 888, 1022), Carthamus sp. (504), Chrysanthemum sp. (181, 363, 568), Citrus sp. (659, 1111), Cucurbitaceae (207, 208, 327, 639, 643, 651, 781, 783, 913, 946, 1071, 1108), Euphorbia (84), flax (423), Glycine max (679, 1073), Gramineae (244, 249, 285, 286, 287, 288, 289, 290, 372, 575, 577, 602, 676, 815, 834, 867, 1025, 1091, 1093), peppers (31), Phaseolus sp. (348, 350, 398, 407, 542, 566, 639, 643, 1128), Salvia sp. (645), sugarcane (131, 132, 137, 138, 362, 602, 603, 784, 789, 954, 1010), tobacco (21, 229, 402, 405), tomato (99, 498, 643, 731, 909, 910, 911), soil and peat (119, 368, 499, 855, 1049), water (883); in South America from Beta sp., Cactaceae (291), Coffea (141), Cucurbitaceae (141, 291), Daucus carota (593), Euphorbia sp., Fragaria sp., peppers (291), Phaseolus spp. (291, 749), Stapelia sp. (618), tomato (141), Zea mays (142, 749); in Puerto Rico from Cucurbitaceae (19), sugarcane (92, 177), Tephrosia sp. (830); in India, Baluchistan and Ceylon from Abelmoschus esculentus (166, 896), Atropa belladonna (994), Cajanus cajan (594), Carica papaya (68, 165, 454, 455, 670, 709, 796, 899, 961), Carthamus sp. (452, 790), Crotalaria sp. (886), Crucifers (42, 206, 587, 588, 589, 1051, 1052), Cucurbitaceae (121, 333, 447, 493, 584, 585, 620, 621, 671, 672, 695, 795, 796, 877, 900), Eleusine sp. and Sesbania (790), flax (879), Ipomoea and Lactuca sativa (592), maize (590), Momordica sp. (796), a number of ornamentals (776), peppers (333, 701), Sesamum sp. (314), Solanum spp. (333, 391, 796, 797), sugarcane (932), Tephrosia sp. (717 a), tobacco (121, 297, 481, 611, 670, 961,1050), tomato (311, 333, 774, 901), Zingiber (360, 672, 726, 871, 875, 998), soil (778), and water (972); in Australia, New Zealand and Papua-New Guinea from Beta sp. (894), Carica papaya (990, 991), Citrus sp. (935), Gossypium sp. (27), Phaseolus spp. and Zea mays (935), and soil (110, 265, 935); in China and Taiwan from Cucurbitaceae (993, 1123, 1124), sugar beet (1077), tobacco, tomato (1124); in Japan from Beta sp. (982), Cucurbitaceae (188, 986), Fragaria sp. (1079), Oryza sp. (439), Phaseolus spp. (39, 986) and soil (977); on the Philippines and Southern Pacific Islands from Colocasia sp., Cucurbitaceae, [p. 37] Phaseolus spp., Solanum spp. (265, 437), sugar beet (4), Talinum sp. (793); in Indonesia and Malaysia from Amaranthus sp. (556, 557), Basella sp. (809), Cruciferae, Cucurbitaceae, Glycine max, Oryza sp., Phaseolus sp. (556, 557), tobacco (323, 324, 335, 336, 457, 458, 638,1096), tomato (557, 992), Vigna sp. and Zea mays (556, 557); in Iraq from soil (13); in Iran from Beta sp. and Citrus sp. (257, 258) and Pisum sp. (478, 479); in Palestine from Cucurbitaceae and tomato (808); in South Africa from Carica papaya (202,1062,1063), tomato and tabacco (1062,1065,1066); in the rest of Africa from Carica papaya, Cucurbitaceae (155, 804), sisal (79), tobacco (90, 91, 111, 112, 254, 411, 415, 456, 971), tomato (804) and Vigna sp. (713). In Europe it was recorded in England from grasses (30); in Czechoslovakia from plant debris, sugarcane (148) and tomato (438); In Poland from Cucurbitaceae (298, 892), in Greece and Cyprus from grasses (699) and tobacco and Solanum sp. (842); in Austria from Beta sp. (268, 652); in Italy from Cucurbitaceae (825); in the USSR from Cucurbitaceae (734, 735).

In many experiments the pathogenicity of P. aphanidermatum was proved. It can cause root rot and damping-off, stalk and rhizome rot, soft rot, fruit rot or cottony blight of Abelmoschus esculentus (166), Basella sp. (809), Carica papaya (899), Catharanthus sp. (452), Carthamus sp. (504), Chrysanthemum sp. (460, 568), Citrus sp. (258, 1111), conifers (329, 351, 803), corn (748), a number of other crops (577), Crucifers (206, 587, 588, 1052), Cucurbitaceae (12, 327, 620, 695, 966, 972, 975, 1123), Leguminosae (398, 478, 479, 679), Fragaria sp. (1081), Gossypium sp. (922), grasses (285, 286, 287, 290, 526, 676, 834, 835, 1092), Ipomoea (349, 592), Lactuca sativa (446), Linum usitatissimum (423, 879), peppers (31), Poinsettia (84), Solanum sp. (697, 806, 807, 1062), sugar beet (257, 1008), sugar cane (556), Talinum sp. (793), Tephrosia sp. (717 a), tobacco (254), tomato (311, 498, 540, 730, 901, 911, 975) and Viola sp. (239, 240).

Temperature has a great influence on infection and damage done by P. aphanidermatum (286, 287, 423, 542, 578, 651, 659, 676, 748, 834, 835, 1004, 1052, 1073, 1080). Temperature of 30-35 C are most favourable for infection, while at lower temperatures it is less or negligible. The discrepancy between positive results of inoculation experiments with flax by Hoyman (423) and Sharma and Nema (879) and negative results obtained by Diddens (198) may possibly be due to lower temperatures used by the latter author. In contrast with Verma (1052) and Mahmud (587), Kendrick (488) did not obtain infection of radish with P. aphanidermatum. P. aphanidermatum can also cause market and storage diseases on various fruits and vegetables, e.g. cucurbitaceous fruits and potato tubers (781, 782, 783, 795, 796).

 

7. Pythium apleroticum Tokunaga

Pythium apleroticum Tokunaga - Trans. Sapporo nat. Hist. Soc. 14: 12. 1935.

Main hyphae up to 3 m wide. Sporangia filamentous, non-inflated, not differing from the vegetative hyphae, usually terminal, occasionally intercalary. Zoospores up to 25 in a vesicle, 8.4 x 4.8 m. Oogonia terminal and intercalary, globose, 11-20 m diam, [p. 38] smooth. Antheridia diclinous, 1-2 per oogonium. Oospores single, aplerotic, globose, 9-17 m diam, wall 0.6-0.8 m thick.

Cardinal temperatures: minimum about 6C, optimum 30C, maximum 40C. Daily growth rate on potato-dextrose agar at 25C: 19 mm.

No material available

Discussion

P. apleroticum differs from P. monospermum, P. papillatum, and P. marinum in having aplerotic oospores, and from P. aquatile, P. diclinum, P. adhaerens and P. dissotocum by its thin oospore walls. P. perniciosum has catenulate hyphal swellings, larger oogonia and both mono- and diclinous antheridia and therefore differs from P. apleroticum. P. tenue has monoclinous antheridia and P. angustatum more antheridia and larger oogonia than P. apleroticum.

Occurrence and pathogenicity

P. apleroticum was originally isolated from Spirogyra sp. in Japan. It seems to be parasitic in Spirogyra sp. and in Sphaeroplea annulinae (441). It has also been recorded from strawberry roots in Japan (1079, 1081).

Fig. 15. - P. aquatile, CBS 215.80. a1-3. oogonia and antheridia, b. sporangial yesicles, c. encysted zoospores. [p. 39]

 

8. Pythium aquatile Hhnk - Fig. 15, 6b.

Pythium aquatile Hhnk - Verff. Inst. Meeresforsch. Bremerh. 2: 94. 1953.

Colonies on cornmeal agar submerged, with an indistinct rosette pattern, on potato carrot agar with a more distinct rosette pattern. Main hyphae up to 6 m wide. Sporangia filamentous or slightly inflated, forming rectangular, dendroid structures; zoospores formed at 20C; vesicles about 30 m diam, discharge tubes up to 200 m long or more, and 4 m wide. Encysted zoospores about 10 m diam. Oogonia globose, smooth, terminal or less often intercalary, but frequently clustering in small groups, 19-23 (-25) m (av. 21 m) diam. Antheridia 1, rarely 2 per oogonium, monoclinous, originating from the oogonial stalk at 2-10 m or more below the oogonium, or from the parent hypha. Oospores aplerotic, 16-19 (-20) m (av. 17.9 m) diam, wall 2-3 m thick.

Cardinal temperatures: minimum 5C, optimum 25C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 17 mm.

Description based on CBS 215.80 which best fits the original description and which is here designated as neotype culture.

Material examined

CBS 214.80, isolated from water from a brook near Grollo-Papenvoort, Netherlands, A.J.P.-N., 1974. CBS 215.80, neotype culture, and 216.80, comm. M. W. Dick, Reading, UK, 1978 (as HCL 137 and HCL 50 respectively) and some other isolates.

Discussion

The isolate CBS 215.80 shows slightly inflated filamentous sporangia, terminal oogonia, mostly single monoclinous antheridia and clearly aplerotic thick-walled oospores. In the cultures many oogonia are produced, but oospores often degenerate before maturity. Intercalary oogonia are rarely present, but clusters of short-stalked terminal oogonia often occur.

Other species in the group with filamentous sporangia and thick-walled aplerotic oospores are P. adhaerens, P. coloratum, P. diclinum, P. dissotocum and P. myriotylum, all with diclinous antheridia. P. perigynosum, which has monoclinous antheridia, has smaller oogonia and a thinner oospore wall. The isolate CBS 214.80 originating from a non-polluted brook in the north-eastern Netherlands, differs from CBS 215.80 by its slightly larger oogonia and from CBS 216.80 by its smaller oogonia.

Occurrence and pathogenicity

P. aquatile was originally isolated from soil from a seawater pool near Kiel, Germany. Since then it has been recorded a few times. Robertson (816) isolated it from soil, Chamaecyparis sp., Neopanax sp., Saintpaulia ionantha, Eucalyptus sp., Thrytomene calycina, Prunus tomentosa, Hebe sp., Cyphonomandra Betacea and Lycopersicon esculentum. Robertson (817) showed it to be moderately pathogenic to tomato seedlings. [p. 40]

Fig. 16. - P. aristosporum, CBS 263.38. a1-4 oogonia and antheridia, b1-3. sporangia, lower magnification, c1-2. appressoria. [p. 41]

 

9. Pythium aristosporum Vanterpool - Fig 16.

Pythium aristosporum Vanterpool - Ann. appl. Biol. 25: 535-537. 1938.

Colonies on cornmeal agar submerged, on potato-carrot agar with a radiate pattern. Main hyphae up to 6.5 m wide. Appressoria commonly produced, sickle-shaped often catanulate. Globose hyphal swellings occasionally present. Sporangia consisting of inflated filaments. Zoospores formed at 20C. Oogonia mostly terminal on short side branches, occasionally intercalary, (sub)globose, smooth, (27-)28-35(-45) m (av. 32.7 m) diam. Antheridia up to 8 per oogonium, club-shaped, crook-necked, mostly about 10-13 x 5 m, monoclinous or diclinous, borne on one or several antheridial stalks. Oospores aplerotic. (21-)24-29(-31) m (av. 26.8 m) diam, wall up to 2(-3) m thick.

Cardinal temperatures: minimum about 5C, optimum 25C, maximum 30C. Daily growth rate on potato-carrot agar at 25C: 22 mm.

Description based on CBS 263.38.

 

Material examined

CBS 263.38 = ATCC 11101, type culture, isolated from Triticum aestivum, Canada, T. C. Vanterpool, 1930. CBS 162.68 = IMI 120402, isolated from Chrysanthemum sp., Ohio, by C. W. Elliott, 1962, comm. G. M. Waterhouse, 1968.

Discussion

P. aristosporum is close to P. arrhenomanes, but differs by the smaller number of antheridia (up to 8 or more in P. aristosporum, up to 20 or more in P. arrhenomanes). In P. aristosporum the antheridia are both mono- and diclinous and in P. arrhenomanes diclinous. Another related species, P. graminicola, has fewer and predominantly monoclinous antheridia and smaller oogonia. The temperature-growth relations in P. aristosporum also differ from those in the other two fungi.

Occurrence and pathogenicity

P. aristosporum has been isolated from a number of the same gramineous plants but seems to occur less frequently than P. graminicola and P. arrhenomanes. Only few records are known after Vanterpool (1938) and all come from Gramineae (267, 550, 925, 1043, 1047) in Canada and the USA.

P. aristosporum has been proved to be pathogenic to a number of cereals, especially at lower temperatures. It has been isolated from dead wheat at 1 C after snow and ice had melted and it caused a serious root-rot under greenhouse conditions at 8-15C (550).

 

10. Pythium arrhenomanes Drechsler - Fig. 17.

Pythium arrhenomanes Drechsler - Phytopathology 18: 874. 1928.

Nematosporangium arrhenomanes (Drechsler) Sideris - Mycologia 23: 272. 1931.

Nematosporangium arrhenomanes var. hawaiiense Sideris - Mycologia 23: 272. 1931.

Nematosporangium spaniogamon Sideris - Mycologia 23: 273. 1931. [p. 42]

Fig. 17. - P. arrhenomanes, CBS 324.62. a1-5. oogonia and antheridia, a4-5 showing the plerotic oospores, b. toruloid sporangium, c1-2. appressoria. [p. 43]

Nematosporangium hyphalosticton Sideris - Mycologia 23: 275. 1931.

Nematosporangium polyandron Sideris - Mycologia 23: 276. 1931.

Nematosporangium thysanohyphalon Sideris - Mycologia 23: 277. 1931.

Nematosporangium rhizophthoron Sideris - Mycologia 23: 279. 1931.

Nematosporangium leucosticton Sideris - Mycologia 23: 281. 1931.

Nematosporangium leiohyphon Sideris - Mycologia 23: 283. 1931.

Nematosporangium epiphanosporon Sideris - Mycologia 23: 283.1931.

Pythium arrhenomanes var. philippinense Roldan - Philipp. Agricst 21: 165-176. 1932.

Pythium arrhenomanes var. canadense Vanterpool & Truscott - Can. J. Res., Sect. C, 6:76-77. 1932.

Colonies on cornmeal agar submerged, on potato-carrot agar with a radiate pattern. Main hyphae up to 6 m wide. Appressoria sickle-shaped, often catenulate. Sporangia consisting of inflated, lobulate filaments, forming complicated structures. Zoospores formed at 20C. Discharge tubes of various lengths, often up to 75 m, mostly about 4 m wide. Encysted zoospores 12 m diam. Oogonia (sub)globose, smooth, mostly terminal, occasionally intercalary, (24-)29-34(-36) (av. 32.5) m diam. Antheridia crook-necked, 12-15 x 6-9 m, making apical contact with the oogonium, many (often 15-20) visible on one oogonium, borne terminally on the branches of 4-8 antheridial filaments, diclinous. Oospores plerotic or nearly so, often abortive, 22-23 (av. 27) m diam. Oogonial wall up to 2 m thick.

Cardinal temperatures: minimum 5C, optimum 25-30C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 23 mm. Description based on CBS 324.62.

Material examined

CBS 293.32, isolated from roots of Saccharum officinarum, Mauritius, 1932. CBS 294.32, type culture of P. arrhenomanes var. canadense, isolated from Triticum aestivum, Saskatchewan, C. T. Vanterpool, 1932. CBS 324.62 = IMI 96342 = ATCC 12531, type culture, isolated from Zea mays, Wisconsin, USA, A. L. Hooker, 1928. CBS 325.62 = IMI 96343, isolated from Saccharum officinarum, Hawaii, 1935. CBS 163.68 = IMI 120410, isolated from Zea mays, USA, A. F. Schmitthenner, 1963, comm. G. M. Waterhouse, 1968.

Discussion

P. arrhenomanes is characterized by the great number of diclinous antheridia. It is close to P. aristosporum and P. graminicola. It differs from the former by the larger number of antheridia which are diclinous, in contrast with the often monoclinous antheridia in P. aristosporum. In P. arrhenomanes the antheridial cells are produced on branches of antheridial stalks and mostly surround the oogonium, more or less forming a ring. P. graminicola has fewer antheridia per oogonium and smaller oogonia. Sideris (1931) described 8 new species and one new variety which all are so close to P. arrhenomanes that they can hardly be distinguished; var. hawaiiense has only slightly thinner oospore walls. Rands and Dopp (1934) and Middleton (1943) already considered them to be synonyms of P. arrhenomanes. Middleton (1943) compared Sideriss species with a number of isolates of various origins. In all of them he found up to 25 diclinous antheridia on branched stalks. The size of the oogonia showed some variation, but in a continuous range. While investigating a larger number of isolates identified as P. arrhenomanes, the present author found the average diameter of the oogonia to vary from 23 to 42 m. In cultures with many abortive oospores it is important, that only well-developed mature oogonia and oospores be measured, as abortive oogonia often have abnormal sizes. [p. 44]

Occurrence and pathogenicity

P. arrhenomanes is a common species, mostly isolated from maize, grasses and sugar cane. It is a typical parasite of gramineous plants, causing root-rot with considerable losses. Its overall distribution is shown on the CMI map No. 420, 1976. It has been recorded from maize in the USA (210, 408, 409, 435, 459, 516, 643, 686, 687, 1047, 1133), Hawaii (461, 462, 728, 889), Canada (74, 1048), and Brasil (140). In addition, wheat, barley and sorghum are the most important hosts in the USA (18, 93, 99, 103, 176, 186, 238, 245, 253, 267, 444, 475, 497, 544, 547, 622, 639, 643, 694, 925, 926, 929, 1068), Hawaii (728, 887, 888), Canada (74, 309, 895, 1048), Brasil (140) and Italy (319). Records of P. arrhenomanes from sugar cane come from the USA (94, 238, 271, 272, 361, 784, 785, 786, 788, 789, 1010, 1113, 1132), Hawaii (606, 887, 954), Mauritius (954, 1099, 1100) and Taiwan (170, 428, 429, 1077, 1082). Further hosts include pineapple (502, 728, 887), species of Billbergia, Cajanus, Commelina, Ipomoea, Musa, Phaseolus, Solanum and in Hawaii (728, 887, 888).

P. arrhenomanes is highly pathogenic to sugar cane (170, 271,272, 428, 429, 784, 789, 1133), maize (243, 408, 409, 459, 461, 462, 789, 1133), wheat (103, 104, 497, 544, 1043, 1047), barley (547) and sorghum (245, 548, 623, 696, 1068). It may be pathogenic to tomato fruits (910, 911), but possibly non-pathogenic or only weakly pathogenic to clover seedlings (338, 339).

Antagonistic effects of other fungi, bacteria and actinomycetes to P. arrhenomanes have been studied, actinomycetes being the most efficient antagonists (328, 334, 461, 462, 463, 464, 563, 1010).

 

11. Pythium buismaniae Van der Plaats-Niterink, sp. nov. - Fig. 18.

Pythium megalacanthum sensu Buisman - Onderzoekingen over de vlasbrand, Diss. Utrecht, P. 42-43. 1927 (non de Bary 1881).

Hyphae principales 3-7 m latae. Appressoria falcata adsunt. Sporangia absunt. Oogonia terminalia in ramulis lateralibus, nonnumquam fere sessilia, spinosa, spinis exclusis (25-)50-70 (in medio 58) m diam; spinae conicae, 1.5-12 (in medio 7) m longae, 2-8 (in medio 4.5) m latae, nonnumquam sursum irregulariter attenuatae. Antheridia singula ad terna, plerumque diclina, e ramulus unius stipitis oriunda; cellulae antheridiales forma variabiles, 18-40 x 9-18 m (in medio 27 x 15 m); stipites saepe ramosi, lobati vel nodosi prope oogonium. Oosporae apleroticae, (20-)40-60(-66) (in medio 51.5) m diam., pariete plerumque 2-4(-7) m crasso.

Typus CBS 288.31, isolatus e radicibus Lini usitatissimi in Neerlandia, a H. A. Diddens, 1937.

Colonies on cornmeal agar forming a meagre aerial myceliuni, often only in scattered wisps; on potato-carrot agar submerged, without a special pattern. Main hyphae 3-7 m wide. Appressoria present, sickle-shaped. Sporangia not formed. Oogonia terminal on short side branches, sometimes almost sessile, spiny, (25-)50-70 (av. 58) m diam; spines conical, 1.5-12 (av. 7) m long, near the base 2-8 (av. 4.5) m diam, sometimes with irregular terminal elongations. Antheridia 1-3 per oogonium, mostly diclinous and borne on branches of one antheridial stalk, which has a tendency to form lobes, diverticles [p. 45] or hyphal knots near or around the oogonium; antheridial cells very variable in shape, 18-40 x 9-18 m (av. 27 x 15 m). Oospores aplerotic, (20-)40-60(-66) (av. 51.5) m diam, wall mostly 2-4(-7) m thick.

Fig. 18. - P. buismaniae, CBS 288.31. a1 -4. oogonia and antheridia, in a1 hyphal outgrowth of oogonial ornamentation, b. coralloid vegetative hypha.

Cardinal temperatures: minimum 5C, optimum 25C, maximum above 30C. Daily growth rate on cornmeal agar at 25C: 10 mm.

Material examined

CBS 288.31, type culture, isolated from Linum usitatissimum roots, Netherlands, H. A. Diddens, 1931. Fresh material of flax roots with oogonia, collected in Noord-Holland and Friesland, Netherlands, 1970. [p. 46]

Discussion

Buisman (1927) identified this species as being nearest to P. megalacanthum but never saw sporangia. Drechsler (1939) who studied her isolate carefully, was also unable to induce sporangium production. The oogonia are much larger than in P. megalacanthum. The antheridia are very complicated with outgrowths and diverticles arising from the antheridial stalk, sometimes entwining the whole oogonium, whilst in de Barys fungus they are more simple in shape. In many oogonia the oospores are abortive. After degeneration of the oospores, the spines of the oogonium enlarge by further terminal growth and may act as normal hyphae. All the authors attempts to obtain sporangia failed. Complicated hyphal branching was often seen, but zoospores were never produced. The antheridia develop simultaneously with the oogonia and soon a very complicated sexual apparatus is formed. The isolation of the fungus is difficult, even when oogonia are visible in the roots of diseased flax plants. The cultivation and maintenance in culture also requires much attention.

Occurrence and pathogenicity

Buisman (109) recognized this species as the cause of vlasbrand, a flax disease characterized by patches (footsteps) in the field where plants are lower and less developed than in the surrounding field. The plants may survive attack but never reach full size.

This species is only known from flax and only recorded from the Netherlands (109, 198, 199, 448, 449, 450, 451), Belgium (198), and Northern France (28). Inoculation experiments showed that it caused the symptoms of vlasbrand (scorch) (109,198, 199, 619), but was not parasitic to other plants. Marchal (599), however, did not find P. buismaniae in diseased flax roots, but Asterocystis radicicola and Thielavia sp. and concluded, that the disease was probably due to different organisms which are all able to cause the symptoms of vlasbrand. Wiersema (1183), however, suggested that Marchal might not have dug out the flax roots carefully enough, leaving the parts of the roots containing the oogonia behind in the soil.

 

12. Pythium catenulatum Matthews - Fig. 19, lc.

Pythium catenulatum Matthews - Stud. Gen. Pythium, p. 47. 1931

Colonies on cornmeal agar at 25 C with a rosette pattern, on potato-carrot agar often with narrow Chrysanthemum pattern. Main hyphae up to 4 m wide. Sporangia consisting of irregularly swollen, branched parts of the mycelium, at 20-25C forming vesicles with 10-20 or more zoospores. Encysted zoospores 9 m diam. Hyphal swellings often present in chains of 3-8, 10-20 m diam, each germinating with 1-3 germ tubes. Oogonia terminal and intercalary, sometimes produced in single cultures, but mostly only after mating of two compatible isolates, spherical, smooth, (19-)20-25(-27) m (av. 22.8 m) diam. Antheridia mostly about 5(-12) per oogonium, diclinous, [p. 48] occasionally monoclinous in homothallic isolates, clavate or crook-necked, making apical contact with the oogonium; antheridial stalks branched bearing one or more antheridial cells. Oospores mostly plerotic, occasionally aplerotic, wall about 1.5 m thick.

Fig. 19. - P. catenulatum, CBS 843.68. a1 -4. oogonia and antheridia, b. irregularly swollen sporangia, c1-3. catenulate hyphal swellings.

Cardinal temperatures: minimum 10C, optimum 30-35C, maximum 40C. Daily growth rate on potato-carrot agar at 25C: 14 mm.

Description based on CBS 843.68 (and dual cultures with CBS 842.68).

Material examined

CBS 842.68 and 843.68, isolated from turf grasses in the USA, W. A. Campbell and F. F. Hendrix Jr., 1948 and 1968, respectively. CBS 461.75, isolated from soil, India, Kapoor, 1975.

Discussion

The presence of catenulate hyphal swellings distinguishes this species from others with swollen filamentous sporangia, such as P. periilum, P. aphanidermatum and P. deliense. Moreover, P. catenulatum lacks the intercalary antheridia of P. aphanidermatum and P. deliense. Most isolates do not form oogonia in single cultures, but in combinations of compatible isolates, a rather sharp white line develops on the junction of the mycelial mats where numerous oogonia occur (Fig. 1c). A temperature of about 25C is favourable for the production of sexual organs (Hendrix and Campbell, 1969). CBS 843.68 formed oogonia in single cultures, but they were more numerous in dual culture with CBS 842.68.

Occurrence and pathogenicity

In the USA P. catenulatum was originally isolated from plant debris in water (616, 643), later also from soil (864) and turf grasses (367). Is has been mentioned a few times from India, viz. on Spirogya sp. in rice fields (48, 121) and sugar cane (167, 930), but also from sugar cane in Taiwan (430, 431), from Lycopersicon esculentum, Solanum melongena, Capsicum annuum and Cyamopsis tetragonoloba in Argentinia (291). It has been shown to cause seedling blight and root-rot of sugar cane (167, 428, 430, 431).

 

13. Pythium chamaehyphon Sideris - Fig. 20.

Pythium chamaehyphon Sideris - Mycologia 24: 33. 1932 (as Chamaihyphon, corrected according to Art. 73A).

Colonies on cornmeal agar showing some low aerial mycelium, on potato-carrot agar submerged with a radiate pattern. Appressoria sickle-shaped. Main hyphae up to 5 m wide. Sporangia subglobose, 18-28 m diam, or oblong; visicles 15-30 m diam, producing up to 25 zoospores; discharge tubes 7 x 4 m. Encysted zoospores 10 m diam. Oogonia terminal and intercalary, smooth, (23-)24-28(-29) (av. 26.5) m diam. Antheridia large, irregular, mostly broadly laterally applied to the oogonium near the oogonial stalk. Oospores aplerotic, (20-)23-26(-27) (av. 24.3) m diam, wall up to 2 m thick. [p. 49]

Fig. 20 - P. chamaehyphon, CBS 259.30. a1-5. oogonia and antheridia, b1-5. sporangia with discharge tubes.

Cardinal temperatures: minimum 5C, optimum 30C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 22 mm.

Material examined

CBS 259.30, type culture, isolated from Carica papaya, Hawaii, C. P. Sideris, 1930.

Discussion

P. chamaehyphon is close to P. vexans, but differs from it by its larger oogonia, the more or less fixed point of contact of the antheridium near the oogonial stalk, and the faster growth. In P. cucurbitacearum the point of antheridial contact is similar but this species has papillate sporangia. P. perplexum has different antheridia and these make contact with the oogonium at various places. - Nothing is known about its geographic distribution or possible pathogenicity. [p. 50]

Fig. 21. - P. coloratum, CBS 154.64. a1-8. oogonia and antheridia, b1-3. filamentous sporangia, c1-3. encysted and germinating zoospores.

 

14. Pythium coloratum Vaartaja - Fig. 21.

Pythium coloratum Vaartaja - Mycologia 57: 417. 1965

Colonies on cornmeal agar submerged, often yellowish or slightly violet, without a special pattern, on potato-carrot agar with a radiate pattern. Main hyphae up to 10 m wide. Sporangia filamentous, terminal and intercalary, occasionally slightly inflated and forming dendroid structures. At 20C forming vesicles up to 60 m diam; encysted zoospores 10-12 m diam. Oogonia (sub)globose or pyriform, terminal or occasionally intercalary, sometimes with a papilla (18-)20-26(-30) m (av. 22.7 m) diam. Antheridia diclinous and monoclinous, 1-5 per oogonium, clavate, crook-necked; 1-2 (rarely more) antheridial cells borne on one stalk, 8-16 x 4-7 m; stalks sometimes more or less encircling the oogonium. Oospores aplerotic, (15-)20-26 m (av. 18.9 m) diam, with yellowish contents and a 2-4 m thick, lilac-coloured wall. [p. 51]

Cardinal temperatures: minimum 5C, optimum 30C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 20 mm.

Description based on CBS 154.64

Material examined

CBS 154.64, type culture, isolated from loamy nursery soil, S. Australia, O. Vaartaja, 1962. CBS 648.79 and 649.79, isolated from Pinus resinosa seedlings, Canada, O. Vaartaja, 1974.

Discussion

P. coloratum differs from its relatives, P. diclinum, P. adhaerens and P. apleroticum, by the presence of both mono- and diclinous antheridia, from P. angustatum and P. tenue by the very thick oospore walls. It differs from P. aquatile by the occasional presence of diclinous antheridia and branched antheridial stalks. In this last respect it can also be distinguished from P. dissotocum.

Occurrence and pathogenicity

This species was originally isolated from soil in S. Australia (1029) and later (1030) from Pinus seedlings in Canada. It has seldom been mentioned since. Robertson (819) recorded it from vegetables and fruits in New Zealand. Vaartaja (1029) showed P. coloratum to be pathogenic to Pinus radiata. It is also moderately pathogenic to a variety of crops (619).

 

15. Pythium deliense Meurs - Fig. 22.

Pythium deliense Meurs - Phytopath. Z. 7: 179. 1934.

Pythium indicum Balakrishnan - Proc. Indian Acad. Sci., Sect. B, 27: 171. 1948.

Colonies on cornmeal agar forming little loose aerial mycelium, on potato-carrot agar submerged mycelium with a vague radiate pattern. Main hyphae up to 8 m wide. Sporangia mostly terminal, occasionally intercalary, consisting of extended, inflated filamentous structures, often with swollen side branches; zoospores formed at 25-30C; discharge tubes of variable length, mostly terminal; encysted zoospores 8-12 m diam. Oogonia smooth, mostly terminal, globose, (19-)20-24 m (av. 21.9 m) diam; oogonial stalks bending towards the antheridium. Antheridia single, rarely two applied to an oogonium, with a straight stalk, terminal and intercalary, monoclinous, occasionally diclinous, antheridial cells about 8 x 8 m. Oospores aplerotic, 16-18(-19) m (av. 17.0 m) diam, wall up to 2 m thick.

Cardinal temperatures: minimum about 10C, optimum 30C, maximum over 40C. Daily growth rate on potato-carrot agar at 25C: 30 mm.

Description based on CBS 314.33, which is designated here as neotype culture. [p. 52]

Fig. 22. - P. deliense, CBS 314.33. a1-6. oogonia and antheridia, b1-3. toruloid sporangia. [p. 53]

Material examined

CBS 194.27, isolated from Nicotania tabacum, Sumatra, S. C. J. Jochems, 1927. CBS 314.33, neotype culture, isolated from Nicotiana tabacum, Sumatra, A. Meurs, 1932. CBS 119.68, isolated from Persea americana, comm. J. Brun, Paris.

Discussion

In 1926 and 1927 S. C. J. Jochems sent two cultures of fungi isolated from diseased tobacco plants in Sumatra to the CBS. These isolates were labelled as presumably representing P. aphanidermatum and P. debaryanum. The latter was maintained in the CBS collection till 1933 as Pythium sp. II. In 1929-1932 Meurs isolated three species of Pythium from tobacco plants in Sumatra suffering from stem-bum: P. aphanidermatum, P. myriotylum and a species similar to the above species II, which he then described as P. deliense. Breda de Haan (1896) in his publication about Phytophthora nicotianae causing stem-burn in tobacco, possibly also dealt with P. deliense as a contaminant in his cultures of Ph. nicotianae.

P. deliense is close to P. aphanidermatum and P. indigoferae. It differs from the former in having oogonial stalks bending towards the antheridium and more slender antheridia, the stalks of which mostly arise as side branches from the oogonial stalk. In P. aphanidermatum the antheridial stalk mostly arises from the parent hypha, or rarely the antheridium is diclinous. The sporangia of P. deliense are less complicated than those of P. aphanidermatum. The sexual stage of P. indigoferae is very similar to that of P. deliense, but in the latter no close connection with the sporangial structures as found in the former is observed; the discharge tubes in P. indigoferae are mostly laterally orientated, while those of P. deliense are terminal. P. deliense and P. aphanidermatum both grow much faster in pure culture than P. indigoferae. P. indicum was said to differ from P. deliense in its more vigorous growth on some media, the tendency to clustering of the oogonia, the production of appressoria and shorter discharge tubes. P. deliense, however, also sometimes forms appressoria and has rather variable discharge tubes. The present author therefore agrees with Kouyeas and Kouyeas (1963) who compared the isolates CBS 194.27 and 314.33 with Balakrishnans original isolate of P. indicum and concluded that they were indistinguishable.

Occurrence and pathogenicity

P. deliense is restricted to warmer regions. Its overall distribution is shown on the CMI Map No. 439, 1968. It was originally isolated from tobacco in Sumatra (638), later also in Nicaragua (229) and Papua-New Guinea (935). Inoculation experiments (47, 458) proved its pathogenicity to tobacco, and also to cucurbits, maize, Amaranthus, Vigna, Hibiscus (47), and melon (522). P. deliense was also recorded in India from tomato seedlings (901), Phaseolus aureus (771), Tephrosia vogelii (717a) and ginger (360), and from Carica papaya, Lactuca indica, Momordica charantia and Vigna sinensis in Sabah, Malaysia (554).

 

16. Pythium diclinum Tokunaga - Fig. 23.

Pythium gracile sensu Middleton - Mem. Torrey bot. Club 20 (1): 31. 1943 [p. non sensu de Bary, 1881; cf. P. 103, 192] .

Pythium diclinum Tokunaga - Trans. Sapporo nat. Hist. Soc. 14: 12. 1935. [p. 54]

Fig. 23. -P. diclinum, CBS 664.79. a1-5. oogonia and antheridia, b1-4. filamentous sporangia, c. vesicle with zoospores, d1-8. appressoria; b at lower magnification. [p. 55]

Colonies on cornmeal agar and potato-carrot agar submerged and with a more ore less radiate pattern. Main hyphae up to 5.6 m wide. Appressoria club-shaped. Sporangia filamentous non-inflated, branched or unbranched. At 5C forming vesicles containing 2 to many zoospores. Encysted zoospores 6-7 m diam. Oogonia spherical or ovoid, smooth, mostly terminal or subterminal, occasionally intercalary, (18-)19-23 (av. 20.5) m diam. Antheridia typically diclinous, 1-2 per oogonium, about 12 x 5 m. Antheridial stalks not branched. Oospores single, aplerotic, 17-19 (av. 17.5) m diam, wall up to 3 m thick.

Cardinal temperatures: minimum 5C, optimum 30C, maximum 35-40C. Daily growth rate on potato-carrot agar at 25C: 19 mm.

Description based on CBS 664.79, which is designated as neotype culture.

Material examined

CBS 526.74, isolated from agricultural soil, Netherlands, I. Blok, 1972. CBS 573.75, comm. D. Ershad, Teheran. CBS 664.79, neotype culture, isolated from Beta vulgaris, Netherlands, A. J. P.-N., 1974.

Discussion

Much confusion exists about P. gracile Schenk. Originally Schenk (1859) observed only filamentous sporangia in a fungus isolated from algae. De Bary (1860) described a fungus from decaying insects which he called P. reptans, but in a foot-note he concluded that this isolate was synonymous with Schenks P. gracile. In 1881 De Bary described another isolate from dead insects which he identified as P. gracile. This isolate produced oogonia and is possibly identical with P. monospermum. The isolates mentioned by Ward (1883) and Petri (1930) are certainly different from Schenks fungus as they produce filamentous inflated sporangia. Butler (1907) gave a further description of P. gracile, but in his concept of the species three forms were included which he named variety a, b, and c, of which variety c was later considered to be a possible synonym of P. aphanidermatum (Matthews, 1931).

The descriptions of P. gracile by Matthews (1931) and Middleton (1943) agree with the cultures of P. diclinum present in the CBS collection, amongst which CBS 664.79 is proposed as the neotype of this species. The description of P. gracile by Middleton (1943) exactly fits that of P. diclinum by Ito and Tokunaga (1935). The latter authors also mentioned 1-2(-3) diclinous antheridia and aplerotic thick-walled oospores. The oogonial diameter is given as 18-25.2 m.

Within the group of species with filamentous non-inflated sporangia, P. diclinum is characterized by its typically diclinous antheridia and aplerotic thick-walled oospores. Only P. apleroticum also has diclinous antheridia but has smaller and thin-walled oospores.

Occurrence and pathogenicity

P. diclinum was originally isolated from young rice plants in Japan. P. gracile has been reported several times but in most cases only the sporangia have been studied and the identifications are uncertain. Nothing is known about its pathogenicity. [p. 56]

Fig. 24. - P. dimorphum, CBS 406.72. a1-5. chlamydospores, b1-12. sporangia, some proliferating.

 

17. Pythium dimorphum Hendrix & Campbell - Fig. 24 and 25, 4a.

Pythium dimorphum Hendrix & Campbell - Mycologia 63: 979. 1971.

Colonies on cornmeal agar submerged, on potato-carrot agar with a conspicuous radiate pattern and some scanty aerial mycelium. Main hyphae up to 10 m wide. Appressoria irregularly subglobose. Sporangia ovoid, elongate, ellipsoidal or clavate, internally proliferating, (35-)42-77(-85) x (19-)25-42(-46) m (av.59.7 x 30.8 m). Zoospores formed at 16C. Encysted zoospores 10-24 m diam. Discharge tubes short. Chlamydospores globose, terminal and intercalary, (26-)43-57(-64) m (av. 50.0 m) diam, wall of uneven thickness, up to 2 m. Oogonia terminal or intercalary, with irregularly spaced, bluntly conical projections of varying length (av. 3.0 m). Antheridia absent or monoclinous. Oospores aplerotic to plerotic, 23-37 (av. 30) m diam. [p. 57]

Fig. 25. -P. dimorphum. a1-3. sporangia, one proliferating, b1-5. oogonia, c1-7. chlamydospores, dl-2. appressoria (reproduced with permission, from Hendrix and Campbell, 1971).

Cardinal temperatures: minimum 5C, optimum 25C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 24 mm.

Description based on CBS 406.72, that of the sexual organs taken from Hendrix and Campbell (1971).

Material examined

CBS 406.72, type culture, isolated from dead roots of Pinus taeda, USA, F. F. Hendrix Jr. and W. A. Campbell, 1971.

Discussion

The large chlamydospores form the most characteristic feature of this species; they sometimes originate from the same hypha as the sexual structures. The wall of the chlamydospores, normally about 1-2 m thick, when mounted in lactophenol-cotton blue can swell to about 4 m. The contour is somewhat unevenly thickened, and irregular mycelial fragments often connect with it. The oogonial projections sometimes cover the whole surface or one side of the oogonia. During the examination no oogonia were produced.

There have been no other records of P. dimorphum. [p. 58]

Fig. 26. - P. dissimile, CBS 155.64. a1-12. oogonia in various stages, in a12 with hypogynous antheridium, in others with antheridium-likes inflations, b1-5. toruloid sporangia, c. vesicle with zoospores, d1-2. free swimming and encysted zoospores, e1-3. appressoria. [p. 59]

 

18. Pythium dissimile Vaartaja - Fig. 26.

Pythium dissimile Vaartaja - Mycologia 57: 421. 1965.

Colonies on cornmeal agar submerged, on potato-carrot agar showing a radiate, sometimes faintly rosette-type pattern. Main hyphae upto 4(-7) m wide. Appressoria sickle-shaped, irregular, often catenulate. Sporangia intercalary or terminal, consisting of complexes of lateral, globose or elongated irregular outgrowths of hyphae, simple or branched. Zoospores formed at 16C. Discharge tubes long and slender, up to more than 100 m long. Vesicles containing few to many zoospores, up to 40 m diam. Encysted zoospores 7-10 m diam. Oogonia intercalary or terminal, often more or less catenulate, globose, smooth, (12-)13-15(-16) m (av 13.8 m) diam. Antheridia mostly completely lacking, rarely hypogynous. Oospores plerotic, wall 1.0-1.5 m thick.

Cardinal temperatures: minimum over 5C, optimum 20-25C, maximum below 30C. Daily growth rate on potato-carrot agar at 25C: 11-13 mm.

Description based on CBS 155.64.

Material examined

CBS 155.64 =ATCC 16515 = Vaartaja 5699, type culture, isolated from soil, South Australia, O. Vaartaja, 1961. CBS 523.74, isolated from soil near Zutphen, Netherlands, A. J. P.-N., 1970.

Discussion

Vaartaja (1965) regarded P. dissimile as closely related to P. torulosum and other species with swollen filamentous sporangia. It is unique in this group because it mostly lacks antheridia, though in rare cases an endogenously formed fertilization tube occurs in the proximal part of the oogonial stalk. In P. torulosum and P. vanterpoolii the young oogonia possess antheridia, but these often disappear soon after fertilization. In P. dissimile, however, the young oogonia lack antheridia entirely. The sporangia consist of complexes of swollen, (sub)globose or irregular, more or less elongated, filamentous parts. Occasionally an oogonium is formed in close connection with a sporangium. In young water cultures zoospores are often produced first from non-swollen filamentous sporangia, followed by the occurrence of swollen sporangia. This feature is not specific for P. dissimile as it also occurs in other species of this group, e.g. P. torulosum.

Occurrence and pathogenicity

P. dissimile has been recorded from sandy soil and Pinus radiata seedlings in Australia (1029) and from soil in the Netherlands (743). It is also known from agricultural soils in Germany (W. Gams, pers. comm.). It seems to be mildly pathogenic to Pinus radiata seedlings (1029).

 

19. Pythium dissotocum Drechsler - Fig. 27.

Pythium dissotocum Drechsler- J. Wash. Acad. Sci. 20: 402.1930; Phytopathology 30:189-197. 1940.

Pythium araiosporum Sideris - Mycologia 24: 38. 1932.

Pythium oryzae S. Ito & Tokunaga, J. Fac. Agric. Hokkaido Univ. 32: 208. 1933.

Pythium perigynosum Sparrow - J. linn. Soc., Bot. 50: 464. 1936. [p. 60]

Fig. 27. - P. dissotocum, CBS 166.68. a1-7. oogonia and antheridia, b1-2. filamentous sporangia, c1-2. vesicles with zoospores, d1-2. appressoria. [p. 61]

Colonies on cornmeal agar submerged, without a special pattern, on potato-carrot agar with a radiate pattern. Main hyphae up to 7 m wide. Appressoria cylindrical or club-shaped. Sporangia filamentous, forming slightly inflated, dendroid structures. Zoospores formed at 5-20C. Discharge tubes up to 11 m long and 4 m wide, widening at the tip to 9 m. Encysted zoospores 8-9 m diam. Oogonia terminal, intercalary or lateral, subglose, often including a small part of the subtending hypha, (19-)21-24(-26) m (av. 22.5 m) diam. Antheridia commonly 1-3(-5) per oogonium, originating from the oogonial stalk immediately below the oogonium and sessile or borne on unbranched antheridial stalks originating at various distances from the oogonium, monoclinous or diclinous. Oospores aplerotic or nearly plerotic, (17-) 18-21(-23) m (av. 19.8 m) diam, wall 1-3 m thick.

Cardinal temperatures: minimum 5C, optimum 20-25C, maximum about 35C. Daily growth rate on potato-carrot agar at 25C: 13 mm.

Description based on CBS 166.68.

Material examined

CBS 260.30, type culture of P. araiosporum, isolated from Carica papaya, Hawaii, Sideris. CBS 379.34, comm. S. Ito, 1934, as P. oryzae. CBS 378.52, isolated by J. H. Warcup, comm. C. J. Hickman, 1952. CBS 166.68 = IMI 120408, isolated from wheat roots, Ohio, USA, A. F. Schmitthenner, 1963, comm. G. M. Waterhouse, 1968. CBS 524.74, isolated from soil, Zuidelijk Flevoland Polder, Netherlands, A. J. P.-N., 1969. CBS 525.74, isolated from rhizome of Iris sp., Lisse, Netherlands, A. J. P.-N., 1967.

Discussion

The main characteristics of P. dissotocum are the non-or slightly inflated, dendroidly branched filamentous sporangia, the low number of antheridia, which can be sac-like, stalked, mono- or diclinous, and the thick-walled aplerotic, or nearly plerotic oospores. The unbranched antheridial stalks separate it from P. adhaerens, P. angustatum, P. coloratum, P. myriotylum and P. monospermum. The presence of both mono- and diclinous antheridia separates it from P. adhaerens, P. aquatile, P. diclinum, P. papillatum and P. apleroticum. P. coloratum has even thicker and coloured oogonial walls. P. periilum has more inflated sporangia and thinner oospore walls. P. tenue has smaller oogonia, P. marinum, P. monospermum and P. papillatum have plerotic oospores.

The type culture of P. araiosporum (CBS 260.30) produces filamentous sporangia and was reidentified by the author as P. dissotocum, even though Middleton (1943) had considered it synonymous with P. debaryanum sensu Middleton. Middleton (1943) studied the type material of P. oryzae and found it to be very similar to P. dissotocum. The isolate CBS 279.34, sent to the CBS as P. oryzae by S. Ito, also agrees completely with Drechslers (1930, 1940) descriptions of P. dissotocum.

Middleton (1950) also found P. perigynosum to be synonymous with P. dissotocum. This species has the same filamentously structured sporangia, a similar antheridial apparatus, terminal and intercalary oogonia and aplerotic oospores. The oogonial papilla mentioned by Ito is not specific as it often occurs in P. dissotocum and other species where part of the subtending hyphae is delimited together with the oogonium. The falcate antheridia described as encircling the oogonia in P. perigynosum by Sparrow (1936) often also occur in wet cultures of other species. The only remaining difference between [p. 62] P. perigynosum and P. dissotocum is the smaller size of the oogonia and oospores of the former, though this can be particularly variable within a species.

Occurrence and pathogenicity

Drechsler originally isolated P. dissotocum from Saccharum officinarum in the USA; later it was recorded several times from sugar cane in the USA (217, 748, 785, 789, 954) as well as from peas, Pilea sp., Beta vulgans, and Spinacia oleracea in the USA (217), conifers in England (1075) and South Australia (1030), Lupinus digitatus and Medicago sativa in Queensland (991) and the USA (856), peach trees (375), ornamentals (363), turf grasses (372) and Carya illinoensis (374), all in the USA, Oryza sativa in Japan (440), Hyacinthus, Iris and Fragaria in the Netherlands (743), and Citrus nobilis and Hydrilla sp. in Sabah (556). It has also been isolated from water in the USSR (634, 635) and the Netherlands (743), and soil in the USA (363, 368), Iceland (469), Lebanon (11) and the Netherlands (743).

Under certain circumstances, P. dissotocum can become pathogenic to sugar cane (784, 789), pecan (374) and peach trees (375), but it has not been found to be pathogenic to conifers (1075) or alfalfa (856).

Fig. 28. P. echinulatum, CBS 281.64. a1-4. oogonia and antheridia, b1-4. sporangia, c1-2. clusters of zoospores. [p. 63]

20. Pythium echinulatum Matthews - Fig. 28.

Pythium echinulatum Matthews - Stud. Gen. Pythium, p. 101. 1931.

Colonies on cornmeal agar submerged with an indistinct rosette pattern, on potato-carrot agar showing a Chrysanthemum pattern. Main hyphae up to 7-8 m wide. Sporangia globose to cylindrical, terminal or intercalary, sometimes in chains of 3 or 4, (10-)20-25(-27) m diam. Zoospores formed at 16C. Discharge tubes 10-21 m long. Oogonia terminal or intercalary, (sub)globose or cylindrical, provided with acute, conical projections (2-)3-5(-11) m long. Oogonia (14-)18-25 (-30) (av. 21) m diam (without projections). Antheridia 1(-4) per oogonium, hypogynous or sometimes monoclinous, rarely stalked. Oospores aplerotic or plerotic, sometimes 2 in an oogonium, wall up to 2 m thick.

Cardinal temperatures: minimum about 5C, optimum 30C, maximum 35-40C. Daily growth rate on potato-carrot agar at 25C: 12 cm.

Description based on CBS 281.64, chains of sporangia according to Matthews (1931).

Material examined

CBS 281.64, isolated from soil in S. Australia, M. Bumbieris, 1964. CBS 556.67 and 239.79, isolated by M. W. Dick, England, 1967. CBS 238.79, isolated from soil, Corsica, France, A.J.P.-N., 1970.

Discussion

P. echinulatum differs from the other species with ornamented oogonia in its rather pointed oogonial projections, typically hypogynous antheridia and sometimes catenulate globose sporangia. The cultures examined produced intercalary sporangia, but chains were not formed. The oospores were mostly plerotic in all isolates.

Johnson (1971) also saw no catenulate sporangia in his isolates. Milnez (1978) compared isolates from the inlet and outlet of Full Lake, Michigan, with CBS 281.64 and identified them as P. echinulatum, despite a rare presence of catenulate (larger) sporangia.

Occurrence and pathogenicity

P. echinulatum was originally isolated from soil in the USA; it is mostly isolated from soil and occurs all over the world. Soil isolates have been recorded from the USA (616, 653), Australia (1030, 1039), New Zealand (816, 817, 819), Iceland (469, 470) and India (778). It has also been isolated from waste of a sewage purification plant in the USSR (634) and water in the USA (655). Only a few records are known from plants: Viola sp. in the Netherlands (239), and strawberry in Japan (1079, 1080, 1081). Pathogenicity tests did not give any evidence of pathogenicithy on Viola (239), but it may attack conifer seedlings (1030); on the other hand, it was found to be very pathogenic to strawberry (1078). [p. 64]

Fig. 29. - P. erinaceus, CBS 505.80. a1-2. oogonia, b1-2. germinating oospores, c1-3. discharging and emptied sporangia, d. encysted zoospores.

 

21. Pythium erinaceus Robertson - Fig. 29.

Pythium erinaceus Robertson - N. Z. Jl Bot. 17: 283. 1977 (as erinaceum, corrected according to Art. 23 ICBN; erinaceus being a masculine substantive).

Colonies on cornmeal agar submerged, showing a rosette pattern. Main hyphae up to 8 m wide. Sporangia globose or subglobose, 12-24 (av. 19) m diam, or ellipsoidal, 12-32 x 7-24 m (av. 22 x 16 m), terminal or intercalary. Discharge tubes 5-7 m wide and 20 m or more long. Oogonia globose or subglobose, 17-29 (av. 22) m diam, terminal or intercalary, ornamented; ornamentations 2-10 (av. 7) m long, straight or curved, tapering, mostly acuminate. Antheridia single, of diclinous origin; antheridial cells inflated, often clavate, 7-12 x 5-10 m (av. 10 x 7.5 m), making broad contact with the oogonium. Oospores plerotic or nearly so, 17-28 (av. 20,5) m diam, with a 0.5-1.5 m thick wall.

Cardinal temperatures: minimum 1C, optimum 20-30C, maximum 40C. Daily growth rate on potato-carrot agar at 20-30C: 7 mm. [p. 65]

Material examined

CBS 505.80, type culture, isolated firm wheatfield-soil in Canterbury, New Zealand, G. I. Robertson, 1975.

Discussion

P. erinaceus is close to P. spinosum, but differs from it by its acuminate oogonial projections, the presence of sporangia and much slower growth. The omamentation is similar to that of P. hydnosporum and the doubtful species P. echinocarpum, but P. erinaceus differs by its plerotic oospores, diclinous antheridia and the presence of sporangia.

Occurrence and pathogenicity

 

 

P. erinaceus was originally isolated from soil in New Zealand. No other records are known. Only one of the three isolates tested by Robertson (820) was pathogenic to pea and wheat, but less virulent than P. spinosum and P. ultimum. The isolates were not pathogenic to tomato and maize seedlings.

 

22. Pythium flevoense Van der Plaats-Niterink - Fig. 30.

Pythium flevoense Van der Plaats-Niterink - Acta bot. neerl. 21: 63. 1972.

Colonies on cornmeal agar submerged, on potato-carrot agar submerged but sometimes with some scanty low aerial mycelium, showing a Chrysanthemum pattern. Main hyphae up to 6 m wide. Appressoria sickle-shaped. Sporangia filamentous, not differing from the vegetative hyphae. Zoospores produced at 5-20C. Oogonia only produced in dual cultures of compatible isolates, mostly terminal on short side branches of feather-like hyphae, smooth, 17-20(-30) (av. 19) m diam. Antheridia diclinous, 1 to several per oogonium, antheridial stalks mostly bifurcate or differently branched near the oogonium, around which they often intricately entwine. Oospores aplerotic, occasionally nearly plerotic, smooth, (14-)16-18(-24) (av. 17.7) m diam, wall 24 m thick.

Cardinal temperatures: minimum 5C, optimum 25C, maximum over 35C. Daily growth rate on cornmeal agar at 25C: 7-10 mm.

Description based on CBS 234.72, sexual organs on cultures mated with CBS 236.72.

Material examined

CBS 234.72 (oogonial, type culture), CBS 236.72 (antheridial), CBS 229.72, 230.72, 231.72, 233.72, 237.72, 238.72, 239.72, all oogonial, isolated from soil in Zuidelijk Flevoland, Netherlands, A.J.P.-N., 1968. CBS 232.72 (oogonial), CBS 235.72 (antheridial), both isolated from different samples of fresh Daphnia sp., Netherlands, A.J.P.-N., 1968. [p. 66]

Fig. 30. - P. flevoense, CBS 234.72 x 236.72 a. position of young oogonia, b1-4. oogonia and antheridia, c1-2. filamentous sporangia with vesicle just before the discharge of zoospores, d1-3. appressoria (reproduced, with publishers permission, from Van der Plaats-Niterink, 1972).

Discussion

Most isolates of P. flevoense originated from Zuidelijk Flevoland polder soil, shortly after this land had been reclaimed. It is the first known heterothallic species in the group with filamentous, non-inflated sporangia. Oospores are formed in dual cultures of compatible isolates on potato-carrot agar with cholesterol, and even more profusely on a medium of potato-carrot agar supplemented with daphnia extract. In the middle of the [p. 67] paired cultures a narrow white line develops (Fig. 1) where the oogonia are produced. Other Pythium species with thick-walled aplerotic oospores, filamentous non-inflated sporangia and diclinous antheridia are P. diclinum and P. adhaerens; P. flevoense differs from both species in being heterothallic; in P. adhaerens the antheridia mostly originate only from one antheridial stalk, while in P. flevoense more antheridial stalks are present on one oogonium. In P. diclinum one or two antheridia may be present which are not so complicated as those of P. flevoense. Other isolates with filamentous, non-inflated sporangia which never form oogonia (group F) cannot by assigned with certainty to a species of Pythium.

P. flevoense may be more common in wet soils, but as it grows slowly, it is not easily isolated in the presence of fast-growing Pythium species.

 

23. Pythium graminicola Subramaniam - Fig. 31.

Pythiumgraminicola Subramaniam - Bull. Agric. Res. Inst. Pusa 177: 5.1928 (as graminicolum).

Pythium graminicola var. stagni Hhnk - Verff. Inst. Meeresf. Bremerh. 2: 98. 1953.

Colonies on cornmeal agar forming very low aerial mycelium, giving a velvety impression, on potato-carrot agar submerged with a fine radiate pattern. Main hyphae up to 6 m wide. Appressoria subspherical or irregular. Sporangia terminal or intercalary, consisting of inflated, filamentous, irregular complexes; zoospores formed at 20C; encysted zoospores 8-11 m diam. Oogonia terminal and intercalary, smooth, globose, (20-)21-24(-25) m (av. 22.3 m) diam. Antheridia 1-3(-6) per oogonium, predominantly monoclinous, occasionally diclinous; antheridial stalks originating at various distances from the oogonium; antheridial cells crook-necked, clavate, 1-2 borne on each antheridial stalk, persistent after fertilization. Oospores plerotic, wall up to 3 m thick.

Cardinal temperatures: minimum 5C, optimum 30C, maximum about 38C. Daily growth rate on potato-carrot agar at 25C: 20 mm.

Description based on CBS 327.62.

Material examined

CBS 327.62 = IMI 91329, neotype culture, isolated from sugar-cane, Jamaica, R I. Leather. CBS 328.62 = IMI 96346, isolated from pine, Hawaii, H. W. Klemmer, 1962.

Discussion

Characteristic features are the several, predominantly monoclinous antheridia, the size of the oogonia and the inflated filamentous sporangia. The oospores are often abortive. According to Lenny and Klemmer (1966), sterols, manganese and zinc are necessary for the production of oogonia, and calcium stimulates the ripening of the oospores.

This species is close to P. arrhenomanes and P. aristosporum, but can be distinguished from these species by fewer antheridia per oogonium and smaller oogonia. Moreover, in P. graminicola the antheridia are predominantly monoclinous. It has larger oogonia and more antheridia per oogonium than the other related species, [p. 68] P. torulosum and P. vanterpoolii, and differs from P. myriotylum by the plerotic oospores and different temperature-growth relations.

Fig. 31. - P. graminicola, CBS 327.62. a1-9. oogonia, some with antheridia, b1-2. toruloid sporangia, c1-3. appressoria.

[p. 69]

Hhnk (1953) distinguished P. graminicola var. stagni, isolated from soil under stagnant seawater near Kiel, Germany, from var. graminicola by its smaller sizes and the occasional presence of diclinous or straight antheridia. These differences are not considered sufficient to recognize a distinct variety.

Occurrence and pathogenicity

P. graminicola was originally described from wheat roots in India. It has been recorded several times, especially from Gramineae on wich it can be an important pathogen. Its overall distribution is shown on CMI Map no. 296, 1954. It has been recorded from species of Zea, Avena, Triticum, Hordeum, Sorghum, Saccharum, Oryza and some other genera in continental parts of the USA (122, 251, 341, 393, 394, 627, 628, 629, 643, 784, 786, 788, 789, 792, 927, 954,1042), Hawaii (2,139, 574, 605, 728), Puerto Rico (517, 518, 554, 824), Jamaica (821), India (595, 777, 794, 878, 932, 962, 963), Japan (1077,1082), the Philippines (712), Mauritius (881), Malaysia (660), Italy (319), and England (30). P. graminicola has also been isolated from Ananas in Hawaii (502, 728), Allium seedings (869), Vicia and Pisum (1089) in the USA, Zingiber and Curcuma in Sri Lanka (26), Curcuma in India (776), Maranta in Argentina (291), and Phaseolus in Brasil (141). It has also been isolated from soil, especially at 5-15 cm depth (507).

Much work has been done on the pathogenicity of P. graminicola. It was found to be pathogenic to a great number of gramineous plants, such as maize (251, 340, 341, 342, 343, 393, 394, 409, 410, 792, 964), sugar cane (931, 932, 933, 934, 1121), wheat, barley, oats and other cereals (106, 107, 341, 343, 357, 395, 580, 595, 777, 835, 878, 927, 952, 953, 962, 965). Also some non-gramineous species were susceptible, viz. Allium (896), Vicia and Pisum (1089), Gossypium and Curcuma (777), Ananas (502) and potato (806, 807). In some cases additive effects were observed due to simultaneous infections of plants by P. graminicola with nematodes (32, 824, 841) or with a virus (518). Antagonistic actinomycetes in the soil can probably reduce the infection of sugar cane with P. graminicola (506, 934). Infection was most severe at about 25C (393, 690, 872, 878).

 

24. Pythium grandisporangium Fell & Master - Fig. 32.

Pythium grandisporangium Fell & Master - Can. J. Bot. 53: 2920-2921. 1975.

Main hyphae up to 6 m wide. Sporangium-bearing branches mostly simple, rarely branching, up to 7 m wide. Sporangia terminal, the long axis often perpendicular to the subtending hypha, irregularly shaped, bursiform to ventriculose, 35-131 x 22-74 (av. 85 x 51) m, with a tapering neck, 22-140 m (av. 62 m) long, papillate; papillae 9-14 (av. 10.5) m diam. Encysted zoospores 7-8 m diam. Oogonia terminal, smooth, globose, 36-45 (av. 41) m diam. Antheridia one to several per oogonium, monoclinous, [p. 70] occasionally diclinous, broadly appressed to the oogonium. Oospores single, plerotic, globose, smooth, 29-36 (av. 33) m diam, wall 2-5 m thick.

Fig. 32. - P. grandisporangium, CBS 286.79. a1-4. oogonia and antheridia, b1-5. pyriform sporangia, lower magnification.

Daily growth rate on cornmeal agar with 1.5% salt concentration at 25C: 10.5 mm, on cornmeal agar in distilled water 5.2 mm.

Material examined

CBS 286.79 = ATCC 28295, type culture, isolated from leaves of Distichilis spicata submerged in 3% seawater in a salt-marsh, dwarf-mangrove area inland from little Card Sound, Florida, J. W. Fell and I. M. Master, 1973.

Discussion

P. grandisporangium was isolated from yellow leaves of Rhizophora mangle submerged in fresh water and yellow leaves of Distichilis spicata and Cladium jamaicense submerged in seawater, all in a salt-marsh, Florida. It can be distinguished from other known species by its large, irregular sporangia, large oogonia and thick-walled oospores. No other records are so far known. [p. 71]

Fig. 33. - P. helicandrum, a1-3. oogonia and antheridia, b1-4. intercalary and terminal sporangia (reprocuced, with permission, from Drechsler, 1950).

 

25. Pythium helicandrum Drechsler - Fig. 33.

Pythium helicandrum Drechsler - Bull. Torrey bot. Club 77: 455. 1950.

Colonies on cornmeal agar submerged, on potato-carrot agar showing a coarse radiate pattern. Main hyphae up to 8 m wide. Sporangia mostly elongated, ellipsoidal or limoniform, mostly terminal, occasionally intercalary, 25-80 x 25-5 5 m. Sporangium-bearing hyphae long, not or sparingly branched. Discharge tubes 10-60 x 4.5-8 m, mostly formed at the distal end of the zoosporangia. Encysted zoospores about 12 m [p. 72] diam. Oogonia globose, terminal, occasionally intercalary, with a spiny ornamentation, (17-)26-30(-32) (av. 29) m diam, excluding the projections; protuberances 2.5-5.3 (av. 3.7) m long and 2-4(-8) m wide at the base, thick-walled near the base. Oogonial stalks 6-45 m long, straight or slightly curved, often entwining the antheridial stalk with 1 or 2 turns. Antheridia single, terminal, diclinous; antheridial stalks 10-50 m long, mostly entwining the oogonial stalk in 1-3.5 turns; antheridial cell elongated, adhering closely to the oogonium over its entire length, 25-45 x 4-7 m, sometimes wound spirally around the base of the oogonium. Oospores globose, (15-)21-27(-30) (av. 22.3) m diam, wall up to 2 m thick.

Cardinal temperatures: minimum about 5C, optimum 25C, maximum below 37C. Daily growth rate on cornmeal agar at 25C: 30 mm.

Description based on CBS 393.54 and the description by Drechsler (1950) for the sporangia and zoospores.

Material examined

CBS 393.54, isolated from Rumex acetosella, Maryland, USA, by C. Drechsler, comm. W. E. Jeffers in 1954. CBS 527.74, isolated from Azalea sp., Aalsmeer, Netherlands, H. Rattink, 1974.

Discussion

Waterhouse (1968) considered Phytophtora stellata (cf. p. 197) to be synonymous to P. helicandrum. Indeed Ph. stellata does not belong to Phytophthora but to Pythium; it does, however, differ from P. helicandrum in that the sporangia of P. helicandrum seem to be non-proliferous and Ph. stellata has monoclinous antheridia, whilst in P. helicandrum they are diclinous. The typical manner in which the oogonial and antheridial stalks wind around each other has not been mentioned or illustrated for Ph. stellata, which is here regarded as a separate species of Pythium.

Occurrence and pathogenicity

Drechsler originally isolated P. helicandrum from Rumex acetosella in the USA. Another record is known from soil in the USA (371).

Nothing is known about the possible pathogenicity of P. helicandrum. There are only a few records of the species. Hendrix at al. (371) found it in forest soils but did not give further information about the isolate.

 

26. Pythium helicoides Drechsler - Fig. 34.

Pythium helicoides Drechsler - J. Wash. Acad. Sci. 20: 413-414. 1930; Phytopathology 29: 408-415. 1939.

Phytophthora fagopyri Takimoto - Bull. sci. Fak. terk. Kjusu Univ. 6: 108. 1935; ex Ito & Tokunaga - Trans. Sapporo nat. Hist. Soc. 14: 15. 1935.

Colonies on cornmeal agar producing cottony aerial mycelium, on potato-carrot agar a more or less radiate pattern. Main hyphae up to 8 m wide. Sporangia terminal, [p. 73] proliferous, subglobose but mostly obovoid, papillate, (18-)27-38(-43) x (13-)16-27 m (av. 31 x 21 m); discharge tubes arising apically, 3-40 x 3-9.5 m; encysted zoospores 10-15 m diam. Oogonia terminal, lateral or intercalary, smooth, (26-)31-38(-40) (av. 33.5) m diam. Antheridia 1-4 per oogonium, borne on simple or branched stalks, sometimes winding around the oogonial stalk or around other hyphae in the neighbourhood of the oogonium. Antheridial cells elongate, 20-42 x 6-9 m, adhering along their length to the oogonium, forming a lateral fertilization tube. Oospores globose, aplerotic, often yellowish (21-)27-32(-33) (av. 30.5) m diam, wall 4-6 m thick.

Fig. 34. - P. helicoides, CBS 286.31. a1-3. oogonia and antheridia, b1-5. elongate sporangia, some proliferating, e1-3. appressoria.

 

Cardinal temperatures: minimum 5C, optimum 30-37C, maximum 43C. Daily growth rate on potato-carrot agar at 25C: 34 mm.

Description based on CBS 286.31.

Material examined

CBS 286.31, isolated from Phaseolus vulgaris, USA, comm. S. F. Ashby, 1931. CBS 293.35, isolated from Fagopyrum esculentum, Japan, S. Takimoto, 1935. CBS 167.68 = IMI 120406, isolated from Honda soil, USA, comm. G. M. Waterhouse, 1931. CBS 343.72, isolated from Gossypium hirsutum, H. Massenot, 1972. [p. 73] .


Discussion

Characteristic of P helicoides are the large, closely adhering antheridia, the papillate sporangia, the fast growth and the peculiar temperature-growth relationships. It is close to P. oedochilum, P. palingenes, P. polytylum and P. ostracodes, but differs from P. oedochilum and P. palingenes by the regular, non-furrowed contour of the antheridia. The coiling of the antheridial stalk about the oogonial branch occurs not only in P. helicoides, but also in P. oedochilum and P. palingenes. It occurs infrequently in P. polytylum and P. ostracodes.

Occurrence and pathogenicity

In addition to the original observation on Dahlia, this species is known in the USA from Citrullus vulgaris (211, 643), Pisum sativum, Spinacia oleracea (643), soil and roots of ornamental plants such as Ilex sp., Pyracantha, Photinia and Azalea sp. (363, 368), pecan trees (374) and sugar-cane rootlets (789), in Australia from seedlings of Gossypium sp., Medicago sativa and Pinus elliottii (991), in Malaysia from Glycine max, Hibiscus sp. and Piper nigrum (556).

It is suspected to cause certain root diseases and damping-off of seedlings of the plants from which it has been isolated, but no further studies on pathogenicity have been carried out

Fig. 35. - P. hemmianium, a1-3. oogonia and diclinous antheridia (redrawn form Takahashi, 1954). [p. 75]

 

27. Pythium hemmianum Takahashi - Fig. 35.

Pythium hemmianum Takahashi - Ann. phytopath. Soc. Japan 18: 117. 1954.

Main hyphae up to 10 m wide. Hyphal swellings terminal and intercalary, globose, doliiform, smooth, 15-36 (av. 29) m diam. Oogonia rarely produced, terminal, smooth, 28.5-36 (av. 32) m diam. Antheridia mostly diclinous, rarely monoclinous, 1-3 per oogonium, making broad apical or lateral contact. Oospores plerotic, smooth, globose, 25-32 (av. 28) m diam.

No material available.

Discussion

P. hemmianum was originally isolated in Japan from Luffa cylindrica in 1947. It can be distinguished from the congeneric P. salpingophorum and P. pleroticum by its much larger oospores and oogonia. The antheridia are similar to those of P. sylvaticum which is heterothallic but occasionally also produces oogonia in single cultures, especially old cultures of female strains. P. hemmianum differs from P. sylvaticum by its plerotic oospores. It has only been recorded from Japan, causing damping-off of Luffa, Cucumis and tomato seedlings (973, 974, 979).

Fig. 36. - P. heterothallicum, CBS 207.68 x 450.67. a1-3. oogonia and antheridia, b1-2. hyphal swellings (reproduced, with publishers permission, from Van der Plaats-Niterink, 1968). [p. 76]

 

28. Pythium heterothallicum Campbell & Hendrix - Fig. 36, lb.

Pythium heterothallicum Campbell & Hendrix - Mycologia 60: 803. 1968.

Colonies on cornmeal agar forming some aerial mycelium, on potato-carrot agar a radiate or vague rosette pattern. Main hyphae up to 7 m wide. Sporangia and zoospores not produced. Hyphal swellings abundant, globose or limoniform, terminal or intercalary, up to 21(-25) m diam. Oogonia globose, terminal and intercalary, mostly only produced in dual cultures of compatible isolates, (20-)22-29(-32) (av. 24) m diam. Antheridia diclinous, up to 8 per oogonium, often forming a complicated knot around the oogonium. Antheridial cells slightly inflated, stalks branched, often bifurcate near the oogonium. Oospores aplerotic, 18-25(-28) (av. 21) m diam, wall 1.5-2 m thick.

Cardinal temperatures: minimum 5C, optimum 25C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 20 mm.

Description based on CBS 450.67 and dual cultures with CBS 451.67.

Material examined

CBS 450.67 (male) and 451.67 (female), type cultures, isolated from soil under Sambucus sp., Canada, F. F. Hendix Jr., 1967. CBS 207.68 (female) and CBS 143.69 (male), isolated from soil near Rhenen, Netherlands, A.J.P.-N., 1966. CBS 208.68 (female), isolated from soil in Costa Rica, Le Poole, 1967. And several other isolates not preserved in the CBS collection.

Discussion

Oogonia are mostly not formed in single cultures but may occur in aged cultures or in isolates which have been maintained in culture for some years. Oogonia then initially appear around the inoculum in female cultures, but rarely appear in male isolates. A sharp white line of oogonia (Fig. lb) forms where compatible isolates meet after about 5 days at 20C, the zone subsequently broadens slightly and sometimes becomes somewhat diffuse towards the female side. The line is thus different from that formed in paired cultures of P. sylvaticum, P. intermedium or P. splendens. P. heterothallicum does not respond sexually to isolates of these three species. Its antheridia are less inflated than in P. sylvaticum and P. intermedium, it does not form the catenulate hyphal swellings of P. intermedium and its hyphal swellings are smaller than those of P. splendens.

Occurrence and pathogenicity

P. heterothallicum was originally isolated from soil in Canada. It has mainly been recorded as a soil saprophyte but seems to occur in several parts of the world, It has been recorded in the USA (365, 368, 371, 466), the Netherlands (740, 743) and New Zealand (816). In addition to the Dutch isolates, the author has also isolated it from soil samples from Ibiza, Sardinia, Czechoslovakia, Germany, Kenya, and Costa Rica.

Nothing is known about its possible pathogenicity. [p. 77]

Fig. 37. -P. hydnosporum, CBS 253.60. a1-4. oogonia; b, c. de Barys slides of Artotrogus hydnosporus from Montagnes type material in BM: b1-3. oogonia, c1-2. sporangia.

 

29. Pythium hydnosporum (Mont.) Schrter - Fig. 37, 6f.

Artotrogus hydnosporus Mont. apud Berk. - Gdnrs Chron. 1845: 640; J. R hort. Soc. 1: 33.1846 (reprinted as Phytopath. Class. 8. 1948) = Pythium artotrogus de Bary - Bot. Ztg 39: 578. 1881 = Pythium micracanthum de Bary - Abh. Senckenb. naturf. Ges. 12: 247. 1881 = Pythium hydnosporum (Mont. apud Berk.) Schrter - Engler & Prantl, Nat. Pfl.Fam. 1(1): 105. 1879.

Pythium artotrogus var. macracanthum Sideris - Mycologia 24: 47. 1932.

? Pythium echinocarpum Ito & Tokunaga - J. Fac. Agric. Hokkaido Univ. 32: 210. 1933 (cf. p. 191)

Colonies on cornmeal agar submerged, on potato-carrot agar without a special pattern. Main hyphae up to 8 m wide. Sporangia and hyphal swellings lacking. Oogonia globose, intercalary, occasionally terminal, (20-)26-33(-34) (av. 29) m diam; wall covered with slender pointed projections, 3-8 m long, at the base 1-2 m diam. Antheridia hypogynous, one or occasionally 2 per oogonium. Oospores plerotic or aplerotic, (18-)23-29(-30) (av. 26) m diam, wall up to 3 m thick.

Cardinal temperatures: minimum 4C, optimum 28C, maximum 35C. Daily growth rate on cornmeal agar at 25C: 34 mm.

Description based on CBS 253.60. [p. 78]

Material examined

Slides prepared from type material (potato tubers) originating from Montagne, by A. de Bary, in BM. CBS 253.60, comm. F. Mach, 1960.

Discussion

De Bary (1876, 1881) considered the genus Artotrogus to be synonymous with Pythium and renamed the fungus P. artotrogus. Fischer (1892) agreed with this change, but Schrter (1897) correctly changed the name to P. hydnosporum. Butler (1906) studied the fungus again and gave a more complete description. The culture CBS 253.60 has slightly larger oogonia and oospores (20-34 and 18-30 m, respectively) than the type material (21-25 and 16-20 m) or that observed by Butler (1907) (18-27 and 15-24 m). The typical oogonia with the slender, acute projections, the hypogynous antheridia, the thick-walled plerotic or aplerotic oospores in CBS 25 3.60, agree well with the type material.

The projections are more slender and pointed than in the other species with spiny oogonia, such as P. oligandrum, P. echinulatum or P. anandrum. Till now sporangia have not been observed in P. hydnosporum, while in the above three species they are readily produced.

Sideris (1932) isolated a Pythium from Ananas which he distinguished as var. macracanthum because of its slightly longer spines, the presence of some epigynous antheridia and the development of some aerial mycelium. The description is not very clear and the differences with the species seem to be small. Waterhouse (1967) considered this variety to be insufficiently different from the species. However, Sideriss illustration shows protuberances which are rather similar to those of P. spinosum.

Occurrence and pathogenicity

P. hydnosporum was originally found on potato tubers. It has been recorded from several plants. It has been isolated on Hawaii from Ananas comosus, Cajanus cajan, Panicum purpurescens, Phaseolus vulgaris, Saccharum officinarum and Vigna sinensis (728, 889, 891), in the USA from Pinus spp. (329, 351), Citrullus vulgaris (783), Saccharum officinarum (236, 954), in England from Apium graveolens (956) and Solanum tuberosum (906), in Germany from Solanum tuberosum (59, 61), in France from Solanum tuberosum (674, 675), in the Netherlands from Pinus nigra, Pseudotsuga menziesii (417), in Bohemia from Nymphaea alba (200), in Sweden from Raphanus sativus (717), in Hungary from Lycopersicon esculentum (673), in India from Solanum tuberosum (120,121, 970) in Norway from Viola tricolor (908), and in Japan from Fragaria sp. (1081). It has also been isolated from water (616), soil (371) and mushroom compost in the USA (261). An isolate reported from wilting poppies and Antirrhinum sp. in S. Africa as P. hydnosporum (1062) was later (1066) reidentified as P. oligandrum, and a similar error cannot be excluded for most of the above records.

Inoculation experiments with P. hydnosporum have been carried out on Pinus sp. (417, 800, 801, 803), Lupinus sp. (863) and sweet potatoes (349), but the fungus was not or only weakly pathogenic to these plants. P. hydnosporum was regarded as the causal agent of a rare tuber-rot of potatoes in Calcutta (797). It was shown to be strongly pathogenic to peas, causing damping-off and watering rot of the roots and the stem base (519). [p. 79]

Fig. 38. - P. hypogynum. a1-4. oogonia with hypogynous antheridia, b1-3. sporangia, b2-3. formation of discharge tube and vesicle, c. a zoospore, d1-3. germination of encysted zoospore (reproduced from Middleton, 1943). [p. 80]

 

30. Pythium hypogynum Middleton - Fig. 38.

Pythium hypogynum Middleton - Mem. Torrey bot. Club 20: 69. 1943.

Pythium acrogynum Y - Acta microbiol. sin. 13: 117. 1973 (cf. p. 185).

Colonies on cornmeal agar showing a radiate pattern. Main hyphae up to 8.3 m wide. Sporangia terminal, occasionally intercalary, (sub)globose, non-proliferating, 6.5-34.5 (av. 22) m diam; discharge tubes about twice the diameter of the sporangia. Oogonia terminal, (sub)globose, smooth, 10-35 (av. 22) m diam, delimiting septum at a distance of 5-30 m below the oogonium. Antheridia strictly hypogynous; antheridial cells 3-11 x 2.8-8.3 m (av. 6.5 x 5.5 m). Oospores plerotic.

Cardinal temperatures: minimum 1C, optimum 31-34C, maximum 37C. Daily growth rate on cornmeal agar at 25C: 11 mm.

No material available.

Discussion

P. hypogynum has, like P. rostratum, P. ultimum and P. pulchrum, hypogynous antheridia. Whilst in P. hypogynum all antheridia are hypogynous, the other three species also have monoclinous and diclinous antheridia. Moreover, P. pulchrum and P. ultimum have aplerotic oospores and P. rostratum mainly intercalary oogonia. P. hypogynum has a radiate growth habit and P. rostratum a rosette appearance. P. hypogynum grows more slowly than P. ultimum and P. pulchrum, but faster than P. rostratum.

Occurrence and pathogenicity

P. hypogynum was originally observed on Hordeumvulgare and Heucheria hispida in the USA (641, 643). It is considered to be pathogenic to cereals (925, 927) but not or only weakly so to Fragaria sp. (705).

Fig. 39. - P. indigoferae. a1-4. various stages of oogonial development (redrawn from Butler, 1907). [p. 81]

 

31. Pythium indigoferae Butler - Fig. 39.

Pythium indigoferae Butler - Mem. Dep. Agric. India, Bot. Ser. 1(5): 73. 1907 = Nematosporangium indigoferae (Butler) Sideris - Mycologia 23: 290. 1931.

Colonies on cornmeal agar and potato-carrot agar submerged. Main hyphae irregular, up to 8 m wide, with lateral, globose or cylindrical, op to 12 m wide outgrowths. Sporangia branched, inflated filamentous, small, with lateral short straight discharge tubes. Oogonia smooth, terminal on curved side branches or on lateral outgrowths, often in close connection with the sporangia, 10-20 m diam. Antheridia monoclinous or rarely diclinous, terminal on straight stalks, sometimes several produced on the lateral processes. Oospores plerotic, smooth, with a very constant size up to 18 m diam.

Cardinal temperatures: minimum 15C, optimum 30C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 8 mm.

Description according to Butler (1907) and Middleton (1943) and partly based on CBS 261.30.

Material examined

CBS 261.30, isolated from Cucumis sativus in India by W. McRae, comm. C.P. Sideris, 1930.

 

 

Discussion

The isolate CBS 261.30 has been in culture for more than 50 years and no longer sporulates. Middleton (1943) investigated the same isolate and found it to agree well with Butlers description of oogonia with 16.3-22.4 (av. 19.2) m diam.

P. indigoferae differs from its relatives, P. aphanidermatum, P. torulosum and P. deliense, by the smaller sporangia and the close connection of the oogonia with sporangial complexes. Bending oogonial stalks occur only in P. deliense and P. indigoferae; antheridia are often typically intercalary in P. deliense and terminal in P indigoferae. In addition, the maximum temperature is 5C lower in P. indigoferae than in P. deliense and P. aphanidermatum.

Occurrence and pathogenicity

P. indigoferae was originally isolated from Indigofera arrecta in Calcutta, India. It may be a saprophyte which can become parasitic under certain conditions. It was found to grow saprophytically in the wax layer of the leaves of Indigofera arrecta. It has only rarely been recorded after the original publication: e.g. on Luffa acutangula in Brazil (168). It has also been listed among Indian fungi (121, 970).

 

32. Pythium inflatum Matthews - Fig. 40.

Pythium inflatum Matthews - Stud. Gen. Pythium, p. 45. 1931.

Colonies on cornmeal agar showing a slightly radiate, on potato-carrot agar a radiate pattern. Main hyphae up to 4 m wide. Sporangia filamentous, inflated, forming irregular [p. 82] or globose outgrowths, often growing out into vegetative hyphae or producing a vesicle and zoospores. Oogonia globose, smooth, terminal and intercalary, (19-) 20-24(-27) (av. 22.5) m diam. Antheridia 1-2 per oogonium, diclinous. Oospores plerotic or nearly so, (18-)19-24(-25) (av. 21.5) m diam, wall up to 3 m thick.

Fig. 40. - P. inflatum, CBS 168.68. a1-5. oogonia with plerotic oospores, b1-2. toruloid sporangia, c. zoospores in vesicle.

Cardinal temperatures: minimum 5C, optimum 30C, maximum 37C. Daily growth rate on potato-carrot agar at 25C: 10 mm.

Decription based on CBS 168.68.

Material examined

CBS 168.68 = IMI 120417, isolated from Saccharum officinarum, Louisiana, USA, A. F. Schmitthenner, 1966. CBS 647.79, isolated from Pinus sp., Canada, 0. Vaartaja, 1977.

Discussion

The isolate CBS 168.68 agrees well with the diagnosis given by Matthews. P. inflatum is a slow-growing species. [p. 83]

Occurrence and pathogenicity

P. inflatum was originally isolated from a decaying seedling in a dish containing Vaucheria sp. Only a few further records are known: from water in Germany (402) and the USSR (635 ), soil in Iceland (469), sugar-cane in Taiwan (1077), strawberry in Japan (1081), and Dodonaea viscosa in New Zealand (816). It was not pathogenic to tomato seeds and seedling roots in the soil, but did cause a moderate infection of tomato roots in laboratory tests (817).

 

33. Pythium intermedium de Bary - Fig. 41, 1d, 8a.

Pythium intermedium de Bary - Bot. Ztg 39: 554. 1881 = Artotrogus intermedius (de Bary) Atkinson - Bull. Cornell Agric. Exp. Stn 94: 233. 1895.

Colonies on cornmeal agar submerged, on potato-carrot agar with or without a vague radiate pattern. Main hyphae up to 7 m wide. Sporangia and zoospores not produced. Hyphal swellings abundant, readily liberated, terminal and sometimes also intercalary, often forming regular, dense chains, formed in basipetal succession at hyphal tips, up to 25 m diam. Oogonia formed in dual cultures of compatible isolates, globose, intercalary or terminal, (18-)19-22(-27) (av. 21.5) m diam, wall thin, smooth. Antheridia diclinous, stalks rather long, branched, often bifurcate near the oogonium; antheridial cells 1-7, inflated, crook-necked. Oospores (13-)16-20(-21) (av. 17.5) m diam, wall 1-2 m thick; sometimes 2 oospores in an oogonium.

Cardinal temperatures: minimum 5C, optimum 20-25C, maximum 30C. Daily growth rate on potato-carrot agar at 25C: about 30 mm.

Description based on CBS 266.38 and dual cultures with CBS 221.68.

Material examined

CBS 266.38, (-), isolated from Agrostis stolonifera, The Hague, Netherlands, A. van Luyk, 1938. CBS 267.38 and 268.38, (-), isolated from Pinus sylvestris and P. nigra var. austriaca, respectively, Netherlands, J. G. ten Houten, 1938. CBS 380.34,(-), isolated from Ricinus communis, from soil in a greenhouse in Baarn, Netherlands, A. Meurs, 1934. CBS 221.68, (+), isolated from soil near Rhenen, Netherlands, A.J.P.-N., 1966. CBS 222.68, (-), isolated from Hyacinthus sp., Lisse, Netherlands, G. J. Saalfink, 1965. CBS 223.68, (+), and 224.68, (-), isolated from diseased Scilla sp., near Egmond, Netherlands, A.J.P.-N., 1967.

Discussion

Sexual organs were not found until 1968 (Van der Plaats-Niterink), but the species was readily distinguished by its catenulate hyphal swellings which are formed in basipetal succession and easily shed. In single cultures, oogonia are rare even at an advanced age. After at least 6 days at 20C, dual cultures of compatible isolates produce a broad line of contact (Fig. 1d) contrasting with those formed in paired cultures of P. splendens, P. heterothallicum or P. sylvaticum. In this line white patches indicate the location of oogonia. The best medium for the production of oogonia is a 1: 1 mixture of cornmeal and potato-carrot agars. As in the other heterothallic species, the oospores are often [p. 84] abortive. Occasionally two oospores are formed in one oogonium. P. intermedium is a fast grower and differs in this respect from P. heterothallicum. On cornmeal agar, the culture forms little or no aerial mycelium and often the surface has a granular appearance due to the abundantly formed hyphal swellings, thus differing from P. sylvaticum which forms much cottony aerial mycelium. The hyphal swellings of P. intermedium are significantly smaller than those of P. splendens. Catenulate hyphal swellings do not occur in P. splendens, P. sylvaticum and P. heterothallicum, but only in P. catenulatum, the latter differing from P. intermedium by the production of filamentous, inflated sporangia. Although the production of sporangia and zoospores by P. intermedium was reported by Matthews (1931) and Middleton (1943), these have never been observed since.

Fig. 41.-P. intermedium, CBS 221.68 x 224.68 or 267.38. a1-4. oogonia and antheridia, b1-6. hyphal swellings, some in chains (reproduced, with publishers permission, from Van der Plaats-Niterink, 1968).

Occurrence and pathogenicity

P. intermedium was originally isolated from dead plant material, but it is a typical soil inhabitant. It has been isolated from soil in England (120, 158), France (120), Germany (120, 203), the Netherlands (203, 636, 740, 743), Ireland (30), the USA (368, 371, 372), Lebanon (11) and Japan (1081). A few records from water are known in Germany (402), the USSR (634) and Egypt (242). It has been recorded from dead or living plant material, viz. in the USA from Begonia (639, 643, 696), fern prothallia (40) and tulips (643), in Canada from Daucus carota (480), in Argentina from Capsicum, flax, Fragaria, grasses, Morus, ornamentals, Phaseolus, Pisum, Pyrus, Ricinus, Lycopersicon esculentum and Ulmus (291), in India from Cyperus (122, 794), in China from [p. 85] Pachyrrhizus (1125), in Australia from conifers (1030) and wheat (544), in England from Heracleum sphondylium (1116), Papaver, Brassica and Sinapis (560), in Ireland from diseased plant material (521), in the Netherlands from Chrysanthemum (109), Aquilegia, Arabis, cucumber, Fragaria, Godetia, Phaseolus, Pisum (636), grasses (570, 572), Hyacinthus (831), flax, flower bulbs, Lepidium, Antirrhinum, Saintpaulia (743), Pinus austriaca (417), Ulmus (1094, 1095), Viola (239, 240, 636), in Belgium from Pyrus communis (600), in Germany from Lepidium, Amaranthus (60, 61), Lupinus, Pyrus (862, 863) and Abutilon (120) and in the USSR from clover roots (582).

Some infection experiments have been carried out. P. intermedium seems to be pathognic to the prothallia of Equisetum, Todea and Ceratopteris (61), cuttings of Chrsysanthemum and Pelargonium (109), pansies (239, 240), Begonia (639, 642), sugar-beet seedlings (black-leg disease, 310), tomato seedlings (677), Cucumis and Lactuca (528) and possibly Pinus (418). Infection was not successful with Lepidium and potato leaves (61), Abutilon (120), wheat (544), Pinus (417), Daucus (480) and Sitka spruce (1075).

Fig. 42. - P. irregulare, CBS 250.28. a1-8. oogonia and antheridia, b1-3. hyphal swellings.

[p. 86]

34. Pythium irregulare Buisman - Fig. 42.

?Pythium equiseti Sadebeck - Verh. bot. Ver.Brandenb. 16: 116-125.1874; Bot Ztg 33: 639-645. 1875; Sber. Ges. naturf. Freunde Berl. 1875: 148-151. (cf. p. 191)

Pythium irregulare Buisman - Root rots caused by Phycomycetes, Diss. Univ. Utrecht, p. 38. 1927; Meded. phytopath. Lab. Willie Commelin Scholten 11: 38. 1927.

Pythium dactyliferum Drechsler apud Rands - Proc. Congr. int Soc. Sugar Cane Technol. 3:122. 1930 (nomen nudum).

Pythium fabae Chenay - Aust J. exp. Biol. med. Sci. 10: 149. 1932.

Pythium irregulare var. hawaiiense Sideris - Mycologia 24: 40, 42. 1932.

Pythium polymorphon Sideris - Mycologia 24: 43. 1932.

?Pythium betae Takahashi - Ann. phytopath. Soc. Japan 38: 309. 1972 (cf. p. 187).

?Pythium kunmingense Yu - Acta microbiol. sin. 13: 119-120. 1973 (cf. p. 193).

Colonies on cornmeal agar forming a moderate amount of aerial mycelium, on potato-carrot agar some aerial mycelium and a radiate pattern. Main hyphae up to 6 m wide. Sporangia globose, 10-20 m diam, terminal and intercalary, seldom produced; encysted zoospores about 8 m diam. Hyphal swellings globose, obovate, limoniform or of irregular shape, terminal and intercalary, up to 25 m diam. Oogonia globose to irregular, intercalary, sometimes terminal, (15-)16-21(-25) (av. 18.5) m diam, smooth or with a varying number of blunt conical or finger-like projections of variable length, mostly 0-5 per oogonium. Antheridia 1-2(-3) per oogonium, monoclinous, mostly stalked and originating at some distance from the oogonium, occasionally sessile, hypogynous, sometimes diclinous; antheridial stalks sometimes branched; antheridial cells 10-15 x 4-5 m, making apical contact with the oogonium. Oospores mostly aplerotic, occasionally plerotic, (14-)15-18(-20) (av. 15.9) m diam, wall mostly 1-1.5 m thick.

Cardinal temperatures: minimum 1C, optimum 30C, maximum 35C. Daily growth rate on cornmeal agar at 25C: 25 mm.

Description based on CBS 250.28.

Material examined

CBS 250.28, neotype culture, isolated from Phaseolus vulgaris, Netherlands, A. Meurs, 1928. CBS 263.30, isolated from Nicotiana tabacum, USA, by W. D. Valleau, comm. C. P. Sideris (as P. polymorphon). CBS 287.31, isolated from Pisum sativum, Netherlands, E. Brandenburg, 1931. CBS 265.38, isolated from sugar beet seedlings, USA, C. H. Meredith, 1931. CBS 269.38, isolated from Agrostis stolonifera, Netherlands, A. van Luyk, 1938. CBS 461.48, isolated by P. Gurkin, Adelaide, Australia, 1948. CBS 469.50, isolated from Lepidium sativum, Netherlands, F. Bloemsma, 1950.

Discussion

P. irregulare is characterized by its ornamented oogonia, which are irregular in shape and show a great variation in size. Sporangia are seldom formed; the antheridia are usually monoclinous and in water cultures often falcate. Mostly 1-2 antheridia are present per oogonium, originating at some distance from the oogonial stalk, but in rare cases sessile or hypogynous antheridia occur. The ratio of ornamented to smooth oogonia varies in the different isolates from less than 10% to more than 50 % ornamented oogonia. High temperatures (33C) often caused abnormal oogonia, reduced the number of ornamented oogonia and increased the number of diclinous antheridia (Biesbrock and Hendrix, 1967). In water cultures the oogonia have a stronger tendency to form projections than on solid media. Most oospores are aplerotic but often a number of plerotic or nearly plerotic oospores are also present In these characters, P. irregulare [p. 87] differs from its congeners, P. ultimum and P. paroecandrum.

P. irregulare var. hawaiiense does not differ sufficiently from the species to be considered as a variety. According to Sideris (1932) it would have larger oospores, fewer C onidia, no zoospores and more strongly developed aerial mycelium. Most of these characters depend on the circumstances. Only the larger oospores may be different from var. irregulare, but this is not sufficient to separate them. P. polymorphon is also identical with P. irregulare as already stated by Kouyeas (1964), Vaartaja (1967) and Ahrens (1971). P. equiseti, P. fabae and P. kunmingense seem to be similar to or identical with P. irregulare.

Occurrence and pathogenicity

P. irregulare is a common soil- and plant inhabiting species and has been recorded from several parts of the world. Its overall distribution is shown on the CMI Map No. 206, 1950. It was originally recorded in the Netherlands from pea roots, Lupinus and cucumber seeds (109), later also from Sinapis, beans (636), flax (199), beet (317, 570, 572), Hyacinthus, Iris, Scilla, Antirrhinum, Ipomoea, Billbergia, strawberry and soil (80, 743). There are many records from the USA from Anthoceros (616), sugar cane (789), ornamentals (363, 504, 639, 643, 696, 697, 813,1016), grasses and cereals (267, 363, 419, 497, 629, 925, 927), spinach (697, 968), peas (1089), rhubarb (644), Atropa belladonna (640), conifers (643, 827), Allium 869, 870), Citrullus (643), lettuce (246), alfalfa (626, 856), peach (375, 376, 663, 664, 665), strawberry (703, 705), cotton (73, 466, 467), carrot (422, 654), celery (948, 950), tomato (499), snapbean (967), rhododendron (404), but also from soil and peat (126, 307, 320, 364, 368, 371, 421, 561, 567, 714, 739, 754, 852, 855) and water (277, 884). In Canada, P. irregulare has been recorded from carrot (53, 480, 487) and soil (85, 86, 1032), in Hawaii from pineapple (502, 728, 889, 891), Cajanus, Canavalia, Helianthus, Phaseolus, Vicia and Ipomoea (728, 889) and sugar-cane (954), in Australia from peas (489), Carica papaya, Lactuca, Medicago, Trifolium (52, 117, 581, 958, 990, 991), Carthamus (957), Daucus (757), Eucalyptus (601) and soil (110, 1030, 1039), in New Zealand from several crops, conifers, ornamentals, Eucalyptus, Nicotiana and soil (816, 819) and willow seedlings (923), in Taiwan from soil (424, 425 ), in Papua-New Guinea from Citrullus (275, 935), in the South Pacific Islands from Colocasia, Piper and Xanthosoma (275), in India (pers. observation) and the Lebanon (11) from soil, in South Africa from pepper, papaya, avocado and Citrus (1062, 1063, 1066, 1067), in Argentina from Cupressus (291) and in Brazil from Cichorium (141). European records include some from Germany from Lupinus (863), Cactaceae (533, 534, 535), wheat, rye and Gerbera (530, 532) and water (402) and from Belgium, England (30, 729), Sardinia (pers. observation) and the USSR (558) from soil,

P irregulare has often been shown to be pathogenic, especially to seedlings, e. g. several Leguminosae: Phaseolus, Vicia, Medicago, etc. (52, 117, 338, 339, 581, 617, 739, 817, 856, 863, 889, 912), many ornamentals (504, 532, 533, 534, 535, 639, 889, 957, 1018), Beta vulgaris (317, 1028, 1061), sugar cane (789), Ipomoea (817, 889), pine seedlings (827, 1030), cereals and grasses (409, 410, 927), cotton (73, 465, 466, 467, 826), various crops (817), tomato sedlings (247, 817), pineapple (502, 889), lettuce (246), rhubarb (644), peach (561, 664), Atropa belladonna (640), Cajanus cajan (889), holly (72), grape vine (110), pecan seedlings (427), willow seedlings (923), cress (113, 114, 115, 116), carrot (421, 422, 480, 487), celery (948, 950), spinach (968), Brassica (967) and cucumber (966). [p. 88]

Fig. 43. - P. iwayami, CBS 156.64. a1-3. hyphal swellings, b1-6. appressoria. - c1-5. oogonia and antheridia, d1-3. sporangia, e1-2. zoospore discharge, f. zoospore, g. germination of encysted zoospore, h1-2. oogonium giving rise to sporangia (reproduced from Hirane, 1960). [p. 89]

 

35. Pythium iwayamai S. Ito - Fig. 43.

Pythium iwayamai S. Ito - Trans. Sapporo nat. Hist. Soc. 14: 13. 1935.

Colonies on cornmeal agar submerged, vaguely radiate, on potato-carrot agar with a faint Chrysanthemum pattern. Main hyphae up to 6.6 m wide. Sporangia terminal, globose, ellipsoidal, ovoid or limoniform, thin-walled, 28-48 x 44 m. Encysted zoospores 9-15 m diam. Hyphal swellings intercalary, 36-48 x 24 m, with a rather thick wall. Oogonia terminal or intercalary, globose, smooth, 23-29 (av. 27) m diam. Antheridia single or occasionally 2 or 3 per oogonium, mono- or diclinous, clavate; antheridial stalks sometimes branched. Oospores plerotic or aplerotic, 19-24 (av. 22) m diam.

Cardinal temperatures: minimum under 5C, optimum 25C, maximum 30C. Daily growth rate on potato-carrot agar at 25C: 14 mm.

Description based on CBS 156.64 and Ito (1935).

Material examined

CBS 156.64, isolated from soil in South Australia, O. Vaartaja, 1962.

 

Discussion

Ito (1935) gave a condensed Latin translation of the description for Pythium sp. by Iwayama (1933). The photomicrographs in Itos paper as well as the figures published by Hirane (1960) show clearly aplerotic oospores, although they were said to be plerotic in the diagnoses. The dimensions of the sporangia, given by Ito (1935), differ considerably from those published by Hirane (1960): 27-50 x 21-29 m. In recent years the culture CBS 156.64 did not produce sporangia or oogonia. So the description was made from the diagnosis and illustrations.

P. iwayamai differs from P. pulchrum and P. rostratum by the absence of hypogynous antheridia.

Occurrence and pathogenicity

P. iwayamai was first isolated in Japan from barley and wheat. There are subsequent records in Japan from wheat and barley (392) and in the USA from wheat (550), soil and conifer seedlings (1030, 1039). P. iwayamai is considered to be one of the causal agents of snow rot of cereals (442, 443).

 

36. Pythium macrosporum - Vaartaja & Van der Plaats- Niterink sp. nov. - Fig. 44, le, 6a.

Hyphae primariae ad 8 m latae. Appressoria magna, curvata. Sporangia globosa vel subglobosa, terminalia vel intercalaria, (12-)24-38(-45), in medio 31 m diam. Zoosporae 15C formantur, tubi evacuationis 8 ad magis 60 x 3-7 m; zoosporae incapsulatae 14-20, in medio 16.5 m diam. Oogonia rara in coloniis singulis, copiosa in combinationibus compatibilibus, zonam conspicuam, 5 mm latam formantia; oogonia levia, globosa, terminalia, rarius intercalaria, (21-)23-27(-30), in medio 24.7 m [p. 90] diam. Antheridia singula ad quaterna, curvata, diclina; stipites simplices vel ramosi, saepe contorti vel inflati; cellulae antheridiales 10-18 x 7-8 m. Oosporae apleroticae, (19-)20-25(-28), in medio 22.5 m diam., panes ad 3 m crassus. Temperatura minima infra 5C, optima 25C, maxima infra 34C; incrementum radiale diurnum in agaro e tuberibus solani et daucis mixto 25C 28 mm.

Typus combinatio CBS 574.80 (+) x 575.80 (-), isolati ex radicibus plantarum ornamentalium in Neerlandia, P. Vink, 1976.

Fig. 44. - P. macrosporum, CBS 574.80 x 575.80. a1-7. oogonia and antheridia, b1-5. sporangia with discharge tubes, c. encysted zoospores. [p. 91]

Colonies on cornmeal agar submerged with some aerial mycelium at the margin, on potato-carrot agar at first coarsely radiate, later with a more or less Chrysanthemum-like pattern. Main hyphae up to 8 m wide. Appressoria large, curved. Sporangia globose or subglobose, terminal and intercalary, (12-)24-38(-45) (av. 31) m diam; zoospores formed at 15C; discharge tubes 8 to over 60 x 3-7 m. Encysted zoospores 14-22 (av. 16.5) m diam. Oogonia sometimes formed in single cultures, more abundant in dual cultures of compatible isolates, forming a conspicious, about 5 mm broad line along the contact zone (Fig. le); oogonia smooth, globose, terminal, occasionally intercalary, (21-)23-27(-30) (av. 24.7) m diam. Antheridia 1-4, crook-necked, diclinous; antheridial stalks simple or branched, often more or less contorted or inflated; antheridial cells 10-18 x 7-8 m. Oospores aplerotic, (19-)20-25(-28) (av. 22.4) m diam, wall up to 3 m thick.

Cardinal temperatures: minimum below 5C, optimum 25C, maximum below 34C. Daily growth rate on potato-carrot agar at 25C: 28 mm.

Description based on CBS 574.80 (+) and CBS 575.80 (-).

Material examined

CBS 574.80 (+) and 575.80 (-), isolated from diseased flower bulb and lily roots respectively, Netherlands; CBS 576.80 (+) and 577.80 (-), isolated from roots and stems of lilies, Netherlands, P. Vink, 1976. CBS 578.80 (+), isolated from Iris roots, Netherlands, P. Vink, 1978. CBS 579.80 (9338D), isolated from peat, Ontario, Can ada, O. Vaartaja, 1977.

Discussion

Several isolates only produced globose sporangia and zoospores. In a number of them some oogonia were developed after prolonged cultivation on artificial media, mostly around the inoculum or in small scattered patches. Oogonia were abundantly formed in compatible crossings, but not in crossings with other known heterothallic species (P. intermedium, P. heterothallicum, P. splendens, and P. sylvaticum). The contact zone of two compatible isolates showed a white, rather broad line in which numerous oogonia were present (Fig. 1e). This species therefore behaves as a heterothallic species. It differs from the known heterothallic species by its thick-walled oospores, the easily formed zoosporangia and large zoospores, and the compact, broad contact line.

CBS 574.80 has arbitrarily been designated as +. In this and the other + isolates the growth was faster than in the - isolates. Oogonia were rarely found in freshly isolated single + cultures and even more rarely in isolates. These oogonia were mostly abortive, while in dual cultures more oospores were formed.

Occurrence and pathogenicity

P. macrosporum was isolated several times from diseased roots and stems of flower bulbs in the Netherlands and from peat in Canada. An isolate from Acer platanoides was received at the CBS in 1978 from the Plant Protection Service in Wageningen; another [p. 92] isolate of unknown origin was received from Dr. A. Koch, Germany. This species is possibly pathogenic to seedlings of Pinus resinosa (O. Vaartaja, pers. comm.).

Fig. 45. - P. mamillatum, CBS 251.28. a1-8. oogonia and antheridia, b1-5. sporangia with discharge tubes, c. encysted zoospores.

 

37. Pythium mamillatum Meurs - Fig. 45.

Pythium mamillatum Meurs - Wortelrot veroorzaakt door schimmels uit de geslachten Pythium en Aphanomyces, Diss. Univ. Utrecht, p. 44. 1928.

Colonies on cornmeal agar forming some aerial mycelium, on potato-carrot agar a vague rosette pattern. Main hyphae up to 6.5 m wide. Sporangia globose, broadly ovoid or ellipsoidal, intercalary or lateral, (17-)18-23(-25) (av. 19.5) m diam, smooth; zoospores formed at about 20C. Discharge tubes 10-28 m long. Encysted zoospores 10 m diam. Oogonia globose or oblong, intercalary or terminal, provided with many [p. 93] protuberances, (13-)15-18(-20) (av. 16) m diam; protuberances obtuse, conical and often curved, 2-6 m long and 2-3 m broad at the base. Antheridia 1(-2 or more) per oogonium, mostly monoclinous, infrequently diclinous, originating at some distance from the oogonium. Antheridial cells clavate, making apical contact with the oogonium. Oospores globose, plerotic, wall 0.8-1.4 m thick.

Cardinal temperatures: minimum under 5C, optimum 25C, maximum 30-35C. Daily growth rate on potato-carrot agar at 25C: 25 mm.

Description based on CBS 251.28.

Material examined

CBS 251.28, isolated from Beta vulgaris, Netherlands, E. Petter, 1928. CBS 381.34 = ATCC 11121, isolated from unknown substrate, Sweden, B. T. Palm, 1934. CBS 209.68 and 214.68, isolated from Zinnia sp., Netherlands, A.J.P.-N., 1967 and 1965. CBS 210.68 and 215.68, isolated from soil near Rhenen, Netherlands, A.J.P.-N., 1966 and 1965. CBS 211.68 and 212.68, isolated from garden and forest soils, respectively, near Baarn, Netherlands, M. Kutkov, 1967. CBS 213.68, isolated from Chionodoxa sp., Netherlands, G. J. Saaltink, 1966. And several isolates not maintained in the CBS collection.

Discussion

P. mamillatum is characterized by its spiny oogonia and globose, ovoid or broadly ellipsoidal, non-proliferating sporangia. In this respect it differs from the other spiny species, P. megalacanthum, P. anandrum and P. prolatum, which form proliferous sporangia, and from the species with lobate sporangia, e.g. P. periplocum. The oogonial projections are rather irregular in shape, length and number. They taper slightly towards the blunt tips and are often curved. In aging cultures also a number of smooth oogonia can be present. The protuberances are different from those of the other species with ornamented oogonia. In the spines are shorter and more regular, in P. spinosum longer and conspicuously cylindrical, in P. oligandrum longer and acute, in P. mastophorum and P. polymastum typically mammiform. P. mamillatum differs from P. hydnosporum, P. echinulatum and P. echinocarpum by its plerotic oospores, and from P. helicandrum by its simple, monoclinous antheridia.

Occurrence and pathogenicity

P. mamillatum was originally described from Beta vulgaris where it caused damping off of the seedlings. Since then, it has often been recorded in many countries: In England from Sinapis sp. (532), Viola sp. (385), in the USA from Ageratum haustonianum, Antirrhinum majus, Aquilegia coerulea, Collinsia bicolor, Geum chiloense, Medicago sativa, Triticum aestivum and Viola tricolor (643), Pelargonium sp. (315), Saccharum offlcinarum (789, 954), Citrullus vulgaris (215) and Allium cepa (869, 870). It has been recorded in Hawaii from Ananas comosus (728, 889), in the Netherlands from Beta vulgaris (636, 744), Zinnia sp., Bromelia sp. and Fragaria (743), in Taiwan from Saccharum offinarum (170), In Brasil from tomato (141), in Japan from Fragaria sp. (978) and in Bambari from Gossypium (172). P. mamillatum has often been found in soil: in India (794), Australia (1039), Iceland (469), England (385), the USA (233, 368, 616, 855), Hati (64, 864), India (776, 778) and the Netherlands (637, 743). It has also been isolated from water in a sewage purification plant in the USSR (634).

In most cases P. mamillatum was considered to be pathogenic, e.g. to Viola sp. (636), in conifer seedlings causing damping-off (1030), in sugar-cane in Taiwan causing poor [p. 94] ratooning together with P. arrhenomanes and P. catenulatum (170); grasses were infected successfully with P. mamillatum (570) and also cuttings of Geranium sp. (315). It may be one of the causal agents of blossom end-rot of Citrullus (215). After artificial infection severe damage was observed in seedlings of lucerne, cauliflower and gherkin, but not in a number of Leguminosae (863). P. mamillatum was regarded as only weakly pathogenic to flax (198, 199). Barton (55, 56, 57) studied its saprophytic activity in soil and noted its absence in acid soils which contained much Trichoderma viride. Some algae (Cladophora sp. and Gloeocapsa sp.) could also be infected with P. mamillatum (716).

Fig. 46. -P. marinum, a1-2. oogonia and antheridia (in a1 papillate), b. two filamentous sporangia with discharge tubes, emerging from a Ceramium frond (reproduced, whith publishers permission, from Sparrow, 1934).

 

38. Pythium marinum Sparrow - Fig. 46.

Pythium marinum Sparrow - Dansk bot. Ark. 8(6): 5. 1934.

?Pythium maritimum Hhnk - Kieler Meeresforsch. 3: 347. 1939.

Main hyphae up to 3.5 m wide. Sporangia filamentous. Vesicles containing 3-6 zoospores; zoospores 7.5 x 4.5 m. Oogonia usually terminal on short lateral branches, globose or slightly ellipsoidal, smooth but occasionally forming a small apical papilla. Antheridia 1 per oogonium, diclinous, 11-13 x 6-8 m. Oospores plerotic, globose, occasionally ellipsoidal, 13-20 x 15-21 m, wall 1.5-2 m thick.

No material available.

Discussion

P. marinum differs from P. monospermum by its thinner oospore walls and diclinous antheridia, from P. papillatum by plerotic oospores and the presence of antheridia. In some ways it resembles P. angustatum but differs from this species in having plerotic oospores and fewer antheridia. [p. 95]

P. maritium, isolated from Ceramium sp. in Germany, would only differ from P. marinum by the possession of monoclinous antheridia. As the description is rather poor and Hhnks material showed only a few oogonia, it is not possible to determine whether these two species are identical.

Occurrence and pathogenicity

P. marinum was originally collected from Ceramium rubrum off the island Laes in Denmark. Since then it has been recorded only a few times viz. from water in purification plants in the USSR (559) and Porphyra perforata (483, 484, 485) and P. miniata (295a). Infection experiments on Porphyra lanceolata and P. schizophylla gave positive results (295a).

 

39. Pythium marsipium Drechsler - Fig. 47.

Pythium marsipium Drechsler - Phytopathology 31: 505. 1941.

? Pythium utriforme Cornu - Annls Sci. nat., Bot., Sr. 5, 15: 13. 1872 (cf. p. 198).

Colonies on cornmeal agar submerged. Main hyphae up to 7.5 m wide. Sporangia globose or asymmetrically utriform, papillate, beaked, often bent and mostly terminal, transversely attached on hyphal branches measuring 20-100 x 3-4 m, occasionally intercalary, 25-70 m diam, proliferating. Encysted zoospores 9-12 m diam. Discharge tubes up to 100 x 2-8 m. Oogonia (23-)27-36(-39) (av. 31) m diam, sometimes subterminal, but mostly intercalary, occasionally catenulate. Antheridia 1-4 per oogonium, diclinous, 10-20 x 8-12 m, making broad apical contact with the oogonium. Oospores aplerotic, (19-)23-31(-33) (av. 26) m diam, wall up to 2.8 m thick.

No material available.

Discussion

P. marsipium differs from the other known species of the genus because of its asymmetrically utriform sporangia which resemble those of Pythiogeton. The discharge of the zoospores, however, takes place as in other Pythium species, by means of a vesicle at the tip of the discharge tube and not in an elongate loose vesicle as in Pythiogeton. Sporangia may be globose as well as utriform. The sexual apparatus of P. marsipium differs from that of other species with proliferous sporangia by its diclinous antheridia, which often become bell-like and make broad apical contact with the oogonium as in P. vexans.

Cornu (1872) named a fungus P. utriforme, which was possibly identical with P. marsipium. It had irregular, utriform or elongated reniform, proliferating sporangia, no sex organs were produced, no measurements or figures were given, so that it is impossible to determine its identity. [p. 96]

Fig. 47. P. marsipium. a1-3. oogonia and diclinous antheridia (at larger magnification), b1-5. sporangia with discharge tubes, before, during (b) and after zoospore liberation (at lower magnification) (reproduced, with permission, from Drechsler, 1941).

Occurrence and pathogenicity

Only a few records of P. marsipium are known after its original isolation from leaves of Nymphaea tuberosa in the USA. Ito (440) isolated it from water from a nursery bed of rice and from a pond in Kyoto, Japan. He mentioned 1-2 antheridia per oogonium and proliferous, globose to pyriform sporangia but did not give any pictures of the fungus. His measurements of the sporangia and oogonia agree with those in Drechslers description. This species has also been reported from water of a sewage purification plant in the USSR (634, 635) and from plants roots in China (424, 425). [p. 97]

Fig. 48. - P. mastophorum, CBS 375.72. a1-6. oogonia and antheridia (a at lower magnification), b1-2. sporangia with discharge tubes. [p. 98]

 

40. Pythium mastophorum Drechsler - Fig. 48, 2a, 7e.

Pythium mastophorum Drechsler - J. Wash. Acad. Sci. 20: 411. 1930; Phytopatology 29: 1005-1011. 1939.

Colonies on cornmeal agar submerged, on potato-carrot agar vaguely radiate (Fig. 2a). Main hyphae upto 8 m wide. Sporangia subglobose, (21-)27-39(-48) (av. 33 m) diam, terminal or intercalary; discharge tubes 15-25 x 3-8 m. Oogonia terminal on short side branches, subglobose, (30-)35-43(-48) (av. 38.5) m diam, covered with conical or mammiform protuberances, 2-8 m long and at the base 2-6 m diam. Antheridial single, diclinous; antheridial stalks often with diverticles, antheridial cells usually terminal, occasionally intercalary, often more or less lobate, making broad apical contact with the oogonium. Oospores (23-)30-36(-45) (av. 34.5) m diam, aplerotic or plerotic, Wall up to 4 m thick.

Cardinal temperatures: minimum 3C, optimum 21C, maximum 27C. Daily growth rate on potato-carrot agar at 25C: 10 mm.

Description based on CBS 375.72.

Material examined

CBS 375.72 = IMI 133677 = VKM-F 1915, isolated from Apium graveolens, England, E. Tiley, 1968. Slide IMI 69826, isolated from Apium graveolens, England, comm. E. R. Wallace.

Discussion

P. mastophorum differs from P. polymastum in its smaller oogonia and oospores, often plerotic oospores and single antheridia, and from the other species with ornamented oogonia by its mammiform oogonial projections. The isolate CBS 375.72 has slightly larger oogonia, oospores and sporangia than Drechslers isolate (oogonia 35-41, av. 35.3; oospores 21-35, av. 29.0); its daily growth rate was less (Drechsler: 24-25 mm), while Middleton (1943) observed a 12 mm daily growth rate.

Occurrence and pathogenicity

P. mastophorum was originally isolated from Bellis perennis in the USA. It is not common. A few further reports come from Calceolaria crenatifolia in the USA (643), Petroselinum crispum and Brassica vulgaris in Argentina (291) and soil of pine plantations in South Australia (190).

 

41. Pythium megalacanthum de Bary - Fig. 49.

Pythium megalacanthum de Bary - Abh. Senckenb. Naturf. Ges. 12: 242-246. 1881; Bot Ztg 39(34): 539-544. 1881.

Pythium megalacanthum var. callistephi Tasugi & Siino - Ann. phytopath. Soc. Japan 10: 292. 1940. Nom. inval., Art. 36.

Sporangia globose, elongated or oval, terminal or intercalary, proliferating internally. Encysted zoospores 18-20 m diam. Oogonia globose, 36-45 m diam, covered with [p. 99] conical, pointed protuberances; spines 6-9 m long and 5-6 m diam at the base, sometimes forming proliferations terminating in swellings, which can act as zoosporangia. Antheridia 0-5 per oogonium, mono- or diclinous; antheridial cells 13.5-17.5 x 11.0-13.5 m, applied broadly to the oogonium. Oospores aplerotic, 27-31 m diam.

Fig. 49. - P. megalacanthum, from de Barys slide 13 at BM. a1-4. oogonia and antheridia, b1-4. sporangia, some proliferating.

Material examined

Slide 13 in de Barys collection preserved at K, type material.

No culture available.

Discussion

According to the type slide, P. megalacanthum has proliferous sporangia and spiny oogonia. The few oogonia observed are 38.5-45 m diam, the spines are conical and have an elongated rather pointed tip, especially prominent in longer spines.

P. megalacanthum differs from the other species with spiny oogonia, aplerotic oospores and proliferous sporangia by its larger oogonia, the more conspicuously pointed spines and more numerous antheridia per oogonium. Tasugi and Siino (1940) described the variety callistephi isolated from Callistephus chinensis. It lacked sporangia but only produced C onidia. As it is often difficult to induce sporangium formation in Pythium species there is no reason to recognize this variety as distinct. [p. 100]

Occurrence and pathogenicity

De Bary originally described P. megalacanthum from cress seedlings in his laboratory in Germany. Since then a few records have been mentioned, but in most cases the identity is not certain. Cejp (143, 145) described the species isolated from garden soil in Bohemia. It has also been recorded in the USA from Erica sinensis, E. regerminans, Euphorbia pulcherrima, Papaver nudicaule, Primula obconica (643), in Hawaii from pineapple (889), in Germany from prothallia of Todea africana and from Veronica hederaefolia (860) and soil (811), in the Netherlands from Pelargonium and Chrysanthemum sp. (746), in England from Lepidium sativum (836), in New Zealand from soil and cabbage (816) and in France from melon (541).

An isolate mentioned in France from parsley (707) seems to be doubtful as no antheridia are described, the spines were shorter and thicker, the oogonia smaller and catenulate hyphal swellings occurred. Another isolate suspected to be the causal agent of the root periderm brown scorch syndrome of Japanese radish (1070), had large oogonia and was said to be related to P. spinosum or P. megalacanthum but from the illustration it seems closer to P. megalacanthum.

 

42. Pythium middletonii Sparrow - Fig. 50.

Pythium proliferum de Bary - Jb. wiss. Bot. 2: 182-189. 1860 (non Schenk 1859); Bot. Ztg 39: 553-563. 1881 = Pythium middletonii Sparrow - Aquatic Phycomycetes, p. 1038. 1960.

Colonies on cornmeal agar submerged, on potato-carrot agar forming a radiate pattern, often vaguely Chrysanthemum-like. Main hyphae up to 8 m wide. Sporangia globose, ovoid or limoniform, proliferating internally, (22-)24-34(-38) x 13-30 m (av. 28 x 22 m). Zoospores formed at 20C. Discharge tubes short. Oogonia mostly intercalary, occasionally terminal (20-)21-24(-27) (av. 23) m diam. Antheridia monoclinous, stalked or often sessile, originating immediately below the oogonium, both diclinous and hypogynous. Oospores aplerotic, (17-)19-21(-25) (av. 20.5) m diam, wall 1.5-2 thick.

Cardinal temperatures: minimum 5C, optimum 25-30C, maximum above 35C. Daily growth rate on potato-carrot agar at 25C: 17 mm.

Description based on CBS 528.74.

Material examined

CBS 293.37, isolated from Gossypium sp., Egyptian Sudan. CBS 528.74, isolated from soil, Zuidelijk Flevoland Polder, Netherlands, A.J.P.-N., 1969.

Slides of the type culture prepared by A. de Bary, preserved at K.

Discussion

De Barys isolate only formed proliferating sporangia and he named it P. proliferum. Later (de Bary, 1881) he found another isolate on cress seedlings in water which also [p. 102] formed sexual organs. There is no evidence that both fungi were identical. Slides of his material are still preserved and show a few proliferating sporangia 22.5-35 x 20-31 m, smooth, intercalary and terminal oogonia 20-26 m diam, and aplerotic oospores 18-23 m diam. The antheridia are both mono- and diclinous. This fungus is identical with P. middletonii. In the subsequent literature various observations on size of the sporangia and discharge tubes have been reported. According to Dissmann (1927) they depend on the culture medium used. As the name P. proliferum is antedated by P. proliferum Schenk, which is considered not to be a Pythium, the species was renamed P. middletonii.

Fig. 50. - P, middletonii, CBS 528.74. a1-8. oogonia and antheridia, a4 with hypogynous antheridium, a7. oogonium with 2 oospores, b1-4. sporangia, some proliferating, c1-2. zoospores just before swarming and encysted; - d-e. de Barys slide of P. proliferatum at BM: d1-8. oogonia and antheridia, e. proliferating sporangium.

Occurrence and pathogenicity

P. middletonii has mostly been recorded from water or submerged animal or vegetable debris and soil. De Bary originally described it from decaying insects in water in which he had grown seedlings of Trapa natans. It has been reported in several parts of the world: Germany (60, 402, 860), the USA (277, 643), e.g. in orchards and conifer nurseries (125, 368, 369, 375), in Australia under Sarothamnus scoparius and Rosa multiflora (817) and clover (52), Britain (434, 1076), India (120, 494, 772), S. Pacific Islands (264, 265), Czechoslovakia (200), Romania (1012), Poland 1129), France (120), Iceland (420, 469), Denmark (569), Australia (182), the USSR (559, 634, 635), the Netherlands (743) and Iraq (13).

P. middletonii is a typically aquatic fungus. Records from diseased material are rare and few studies have been carried out on its possible pathogenicity. Nevertheless, it may be pathogenic to conifer seedlings (1030), cabbage (206, 903), tomato and Ipomoea sp. (817). It was also regarded as the causal agent of damping-off of seedlings of jute in Pakistan (46) and of severe damping-off of soybeans in Egypt (241).

Fig. 51. - P. monospermum, CBS 158.73. a1-8. oogonia and antheridia with plerotic oospores, b1-3. filamentous sporangia. [p. 103]

 

43. Pythium monospermum Pringsh. - Fig. 51.

Pythium monospermum Pringsh. - Jb. wiss. Bot. 2: 288. 1858; Mber. dt. Akad. Wiss. Berlin 1858: 298-300 = Nematosporangium monospermum (Pringsh.) Schrter- Engler & Prantl. Nat. PfiFam. 1(1): 104. 1897 = Nematosporangium monospermum (Pringsh.) Jacz. - Opredelitel Gribov, I. Fikomitsety, p. 97, 1931.

Pythium gracile Schenk sensu de Bary - Jb. wiss. Bot. 2: 182. 1860.

Pythium reptans de Bary - Jb. wiss. Bot. 2: 189. 1860.

?Pythium fecundum Wahrlich - Ber. Dt. bot. Ges. 5: 243. 1887 (cf. p. 191).

Pythium complens Fischer - Rabenh. KryptogFl. 1(4): 398. 1892.

Pythium akanense Tokunaga - Trans. Sapporo nat. Hist. Soc. 12: 122. 1932.

Colonies on cormmeal agar showing a radiate or a vague Chrysanthemum pattern, on potato-carrot agar a fine Chrysanthemum pattern. Main hyphae up to 7 m wide. Sporangia strictly filamentous, non-inflated, branched or unbranched. Zoospores formed at 5-18C. Oogonia terminal or intercalary, smooth, globose, (12-)14-16(-18) (av. 15) m diam. Antheridia 1-2(-4) per oogonium, monoclinous and diclinous, stalks when monoclinous originating at various distances from the oogonium; antheridial cells making rather broad apical contact with the oogonium. Oospores plerotic, wall 1-2 m thick.

Cardinal temperatures: minimum 5C, optimum 25C, maximum 30-35C. Daily growth rate on potato-carrot agar at 25C: 5 mm.

Description based on CBS 158.73, which is designated as neotype.

Material examined

CBS 158.73, neotype culture, comm. M. W. Dick, Reading, 1973 as No. 414a. CBS 380.79, isolated from water of the river Vecht, near Ommen, Netherlands, G. Oosterbos 1979. CBS 382.79, isolated from unknown substrate, East Lansing, Mich., K. ODonnell, 1979. CBS 381.79, isolated from soil near the river Yssel, near Zutphen, Netherlands, A.J.P.-N., 1970.

Discussion

P. monospermum is the type species of the genus. It was originally described together with P. entophytum (which was later transferred to the genus Lagenidium by Zopf (1890)). The isolate CBS 158.73 was chosen as the neotype because it most closely fitted Pringsheims original description. In the group of Pythium species with filamentous noninflated sporangia, only P. monospermum, P. papillatum, P. marinum and P. myriotylum have plerotic oospores. P. papillatum has larger and sometimes catenulate oogonia and no antheridia, whilst P. monospermum possesses 1-2(-4) mono- and diclinous antheridia per oogonium. P. marinum has only one diclinous antheridium. P. myriotylum has slightly swollen, finger-like sporangia and complicately branched antheridial stalks.

P. reptans sensu De Bary (1860), regarded as identical with P. gracile Schenk, was described without sexual organs by De Bary (1860); but the strain subsequently found (De Bary, 1881) and preserved in permanent slides by De Bary (at BM), is a P. monospermum. The original descriptions of P. complens and P. akanense fit perfectly P. monospermum. The synonymy of P. fecundum Wahrlich with P. monospermum is less certain, although Fischer (1892), followed by Butler (1907), Matthews (1931) and Middleton (1943) considered them synonymous. While a number of features of P. fecundum resemble those of P. monospermum (filamentous sporangia, antheridia), the [p. 104] oospores as figured by Wahrlich not only show more than one oospore in the oogonium but also an irregular shape of the oogonium itself and thinner oospore walls. A few oospores in an oogonium occur sometimes in a few Pythium species, e.g. P. violae, P. angustatum, P. pulchrum, P. echinulatum and, commonly, in P. multisporum. As no material of P. fecundum is available, its synonymy with P. monospermum remains doubtful.

Occurrence and pathogenicity

P. monospermum was originally isolated from dead insects in water in Germany; it is known to occur over large parts of the world. It has been isolated from dead insects in water and other water samples in England (1076), France (187), the USA (616, 643), Japan (972), Germany (402), the USSR (559, 634, 635), India (494) and the Netherlands (743); several records are known from soil: California (352, 353, 354, 355) and other states of the USA (616, 643, 799), Madeira (403), England (30), Iceland (469) and the Netherlands (743). In several cases P. monospermum has been isolated from plants: Nicotiana tabacum in Java (770), Spinacia oleracea and Richardia aethiopica in the Netherlands (636), sugar cane in the USA (784, 789, 954), rice seedlings in Japan (440), Persea americana and Hordeum vulgare in the USA (355, 643), Lepidium sutivum and Zingiber officinale in India (122), decaying plants in Czechoslovakia (148), and roots of several plants in Australia (816, 817).

Not much is known about its possible pathogenicity. Inoculation experiments on cabbage by Drechsler (206) did not result in disease symptoms. Fischer (266) mentioned that according to De Barys studies, P. complens was not pathogenic to algae. P. monospermum may be pathogenic to sweet potato and potato tubers (975).

 

44. Pythium multisporum Poitras - Fig. 52.

Pythium multisporum Poitras - Mycologia 41: 191. 1949.

Colonies on cornmeal agar submerged, radiate, on potato-carrot agar radiate, slightly zonate. Main hyphae up to 8 m wide. Sporangia (sub)globose or pyriform, proliferating, terminal, (18-)27-38(-54) x (12-)16-27(-38) m (av. 35.5 x 23.5 m), formed on often very long, about 4 m wide, hyphal branches; zoospores formed at 20C; discharge tubes 1(-2) per sporangium, often more of less lateral, 2-3 m long, 4-5 m wide. Encysted zoospores 8-17 m diam. Oogonia smooth, (sub)globose, limoniform, oblong or irregularly shaped, terminal or intercalary, each containing 1-2 (or more) oospores. Unisporous oogonia (19-)24-36(-47) (av. 29.5) m diam, multisporous oogonia often irregularly shaped and over 45 m diam. Antheridia 1-3 per oogonium, monoclinous, hypogynous and diclinous. Oospores plerotic, (16-)19-30(-36) (av. 24.5) m diam.

Cardinal temperatures: minimum 5C, optimum 25-30C, maximum 40C. Daily growth rate on potato-carrot agar at 25C: 15 mm.

Material examined

CBS 470.50, type culture, isolated from soil, Illinois, USA, W. Poitras, 1947. [p. 105]

Fig. 52. - P. multisporum, CBS 470.50. a1-5. oogonia and antheridia, some hypogynous, b1-8. sporangium with discharge tubes and proliferations, b8 zoospores just after disappearance of the vesicle. [p. 106]

Discussion

The most obvious character in P. multisporum is the occurrence of more than one oospore in an oogonium. This is not exceptional in the genus, however, as in other species sometimes double oospores are also formed, e.g. in P. violae, but the occurrence of a larger number of oospores per oogonium seems to be unique for P. multisporum.

Occurrence and pathogenicity

This species has not been recorded after the original description. Nothing is known about its possible pathogenicity.

 

45. Pythium myriotylum Drechsler - Fig. 53, 8c.

Pythium myriotylum Drechsler - J. Wash. Acad. Sci. 20: 404. 1930; Phytopathology 33: 261-276. 1943.

Pythium polyandrum van Hall - Meded. Inst. PlZiektk. 67: 46. 1925 (nomen nudum) (non Nematosporangium polyandron Sideris 1931).

Colonies on cornmeal agar without a special pattern, on potato-carrot agar conspicuously radiate. Main hyphae up to 8.5 m wide; appressoria clavate, knob-like or sickle-shaped, often up to 60 x 11 m,usually formed in clusters. Sporangia terminal or intercalary, filamentous, consisting of undifferentiated and inflated lobulate or digitate elements of variable length and mostly 7-17 m wide. Zoospores formed at 20C. Discharge tubes up to and more than 100 m long, 2-4 m wide. Encysted zoospores 10-12 m diam. Oogonia (sub)globose, terminal or intercalary (20-)26-32(-35) (av. 29) m diam. Antheridia 3-6(-10) per oogonium; stalks branched, often more or less loosely enveloping the oogonium, diclinous, occasionally monoclinous, originating at various distances below the oogonium; antheridial cells clavate or crook-necked, making apical contact with the oogonium, mostly 8-30 x 4-8 m. Oospores aplerotic, colourless or yellowish, (18-)20-27(-29) (av. 24.5) m diam. wall up to 2 m thick.

Cardinal temperatures: minimum 5C, optimum 37C, maximum above 40C. Daily growth rate on potato-carrot agar at 25C: 28 mm.

Description based on CBS 254.70.

Material examined

CBS 315.33, isolated from Nicotiana tabacum, Sumatra, A. Meurs, 1933. CBS 254.70, isolated from Arachis hypogaea, Israel, Z. R. Frank, 1970. CBS 695.79, isolated from Vigna sinensis, Malaysia, P. Liu, 1y 5. CBS 114.77, isolated from diseased fern prothallia, Netherlands, A.J.P.-N., 1977.

Discussion

P myriotylum produces more of less inflated, sometimes digitate, branched sporangia, and forms typical clusters of large appressoria which when young adhere to the bottom of the Petri dish by their apices and are visible as small globose bodies from below. The oogonia are often entangled by a large number of diclinous antheridial stalks which [p. 107] often form several antheridial cells. This species is closely allied to P. aristosporum but lacks monoclinous antheridia entirely. It differs from P. arrhenomanes by its diclinous antheridia and plerotic oospores. The high maximum temperature is typical of P. myriotylum. Only a few of the species in the group with inflated filamentous sporangia can grow at 40C, viz. P. aphanidermatum and P. deliense, but these species differ from P. myriotylum by their typically intercalary antheridia.

Fig. 53. - P. myriotylum, CBS 254.70. a1-3. oogonia and antheridia, b1-2. filamentous slightly inflated sporangia, c1-6. appressoria, c1-5 lower magnification, c as seen through the bottom of the plate, c6 showing the point of attachment in lateral view. [p. 108]

Van Hall (1925) mentioned P. polyandrum (nom. nud.) isolated from tobacco in Indonesia which was stated to be identical with P. myriotylum by Meurs (1934).

The CBS isolates agree well with the description of Drechsler; however, he observed slightly smaller oogonia and oospores: av. 26.5 and 20.8 m, respectively. This may be due to the use of different media.

Occurrence and pathogenicity

P. myriotylum was originally described from Lycopersicon esculentum in the USA. It occurs mainly in warmer regions but has sometimes been isolated from plants cultivated in glasshouses in the temperate zones. It has been isolated in the USA from tomato (211, 219, 575, 910, 911), Cucumis sativus (211, 219), Citrullus vulgaris (211, 219, 783), Solanum melongena (211, 219), Arachis hypogaea (302, 751, 1106), Secale cereale (575), Phaseolus vulgari (312, 566), Caladium hortulanum (813), possibly Robinia pseudacacia (1090) and soil (368). It has also been found in Sumatra on Nicotiana tabacum (335, 638), in Africa on Phaseolus vulgaris (197), papaya (1066), in Australia on Lucerne (989), conifer seedlings (1030) and Carthamus tinctorius (957), in Papua-New Guinea on Nicotiana tabacum (265), in India on Zingiber officinale (875, 1027) and Cyamopsis tetragonoloba (771), in Japan on strawberry (1078, 1081), in Brazil on Sechium edule, Daucus carota, Solanum tuberosum, Abelmoschus esculentus, Solanum melongena, Phaseolus vulgaris, Raphanus sativus and Cucurbita pepo (141), in Israel (278) and Libya (762) on peanuts, and in the Netherlands on young fern plants grown in a glasshouse (pers. observation).

P. myriotylum can be pathogenic to several plants, especially at higher temperatures (553). It is considered to be the main causal agent of pod-rot of peanuts (62, 278, 279, 280, 281, 282, 283, 284, 299, 300, 301, 302, 303, 304, 305, 306, 337, 577, 751).

Experiments have shown an antagonistic relationship between P. myriotylum and Rhizoctonia solani (304, 305) and synergistic effects in plant attack between P. myriotylum and Fusarium solani or Meloidogyne arenaria (282, 299, 300, 301, 565).

In inoculation experiments P. myriotylum was also pathogenic to Phaseolus vulgaris (312, 313, 576, 577), tomato (576, 577, 845, 846, 910, 911), lucerne (989), ginger (875), rye (553, 576, 577, 667, 845), wheat, oats, Lolium multiflorum, cucumber, soyabean, sorghum, tobacco, cabbage and maize (576, 577, 912), pecan trees (374), Carthamus tinctorius (957) and Caladium hortulanum (813). P. myriotylum was suspected to cause a blossom end-rot of Citrullus vulgaris (207).

A toxin was found in P. myriotylum which caused leaf necrosis and stunting of tomato plants (184). [p. 109]

Fig. 54. - P. nagaii. a1-2. oogonia and antheridia, b1-4. sporangia, b1-2 dormant, b proliferating and discharging zoospores, b4 general view showing various stages, c. free-swimming zoospores (reproduced from Ito and Tokunaga, 1933).

 

46. Pythium nagaii S. Ito & Tokunaga - Fig. 54.

Pythium nagaii S. Ito & Tokunaga - J. Fac. Agric. Hokkaido Univ. 32: 209. 1933.

Main hyphae up to 4 m wide. Sporangia terminal, ovoid, pyriform, occasionally globose, 24-36 x 20-26 m, proliferating. Further sporangia also formed on branches of [p. 110] the primary fertile hyphae, originating just below the primary sporangium. Discharge tubes apical, short. Encysted zoospores on average 9.5 m diam. Oogonia terminal, globose, sometimes irregular in shape, smooth, 14-22 m diam. Antheridia single, monoclinous, more or less globose, clavate, slightly curved and soon disappearing after fertilization. Oospores aplerotic, 12-19 m diam, wall 0.8 m thick.

Cardinal temperatures: minimum below 9C, optimum 28C, maximum about 35C. Daily growth rate on cornmeal agar at 25C: about 25 mm.

No material available.

Discussion

In the group of species with proliferating sporangia, P. middletonii, P. salpingophorum and P. nagaii have oogonia less than 30 m diam. P. nagaii differs from P. salpingophorum by its aplerotic oospores, and from P. middletonii by its thin oospore walls.

Occurrence and pathogenicity

P. nagaii was originally isolated from diseased rice seedlings. From pathogenicity tests the authors concluded that, besides other pathogens, P. nagaii could also cause root rot of rice seedlings. Some other records of P. nagaii also come from rice in the USA (238) and Eastern Asia (188).

 

47. Pythium oedochilum Drechsler - Fig. 55, 6c.

Pythium oedochilum Drechsler - J. Wash. Acad. Sci. 20: 414. 1930; Phytopathology 31: 478-486. 1941.

Colonies on cornmeal agar submerged or with some aerial mycelium, on potato-carrot agar without a special pattern. Main hyphae up to 6.5 m wide. Appressoria often present. Sporangia proliferating, subglobose, limoniform, obovoid or ovoid. Oogonia mostly terminal, occasionally intercalary, smooth, (22-)31-36(-39) (av. 32.8) m diam. Antheridia 1-2(-4) per oogonium, mostly diclinous, sometimes monoclinous, curved, elongate, often wavy in contour, applied lengthwise to the oogonium over their total length, (12-)20-26(-30) x 5-6(-8) m. Oospores aplerotic, (20-)28-34(-38) (av. 30.3) m diam, wall 1.4-5 m thick.

Cardinal temperatures: minimum 10C, optimum 30C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 20 mm.

Description based on CBS 292.37.

Material examined

CBS 292.37, comm. C. Drechsler, 1937. CBS 597.68, comm. G. Martin, Rip. Congo, 1968. CBS 252.70, isolated from soil, Wageningen, Netherlands, I. Blok, 1970. [p. 110]

Fig. 55. -P. oedochilum, CBS 292.37. a1-6. oogonia and antheridia, b1-4. sporangia with proliferations, c1-5. appressoria. [p. 112]

Discussion

The most obvious characteristics are the large antheridia with undulating contours, closely applied over their entire length to the large oogonia and the proliferating ovoid or obovoid papillate sporangia. P. oedochilum is closely related to P. heliciodes, P. palingenes, P. ostracodes and P. polytylum. It differs from P. helicoides by the wavy contour of its antheridium, from P. palingenes by the mostly terminal oogonia, from P. ostracodes by the mostly monoclinous antheridia and aplerotic oospores and from P. polytylum by its ovoid or obovoid sporangia, contrasting with the globose sporangia of P. polytylum.

Occurrence and pathogenicity

Drechsler originally isolated P. oedochilum from Dahlia sp. and later from Citrullus vulgaris (215) and Bidens aristosa (218). It has further been isolated from Citrullus vulgaris, Daphne odora and Matthiola incana in the USA (643), from Brassica oleracea in India (771), mango, peppers, and gombo in the Congo Republic (804), and Fragaria sp. in Japan (978, 1081). There are records from soil in Australia (755), the Netherlands (743) and the USA (368).

In pathogenicity. tests P. oedochilum was found to be pathogenic at least to some of the above plants, viz. tomato, aubergine, pawpaw, tobacco and groundnut, while cotton and kenaf were less susceptible (804). It can also attack strawberry (978) and potato tubers (807).

 

48. Pythium okanoganense Lipps - Fig. 56.

Pythium okanoganense Lipps - Mycologia 72: 1127-1128. 1980.

Colonies on cornmeal agar submerged, on potato-carrot agar without a special pattern. Main hyphae up to 8 m wide. Appressoria rare and small. Sporangia terminal, globose, subglobose or pyriform, infrequently proliferating, 30-35 m diam, borne in sympodial succession. Zoospores formed at 0.5-10C; discharge tubes 3-25 m long. Zoospores (8-)10-18(-24) m long, after encystment 11-14 m diam. Oogonia (sub)globose, smooth, terminal on short lateral branches, rarely becoming intercalary after continued outgrowth of a hypha, (15-)24-30(-32) (av. 26) m diam. Oogonial wall rather unequal in thickness. Antheridia 1(-3) per oogonium; antheridial cells 6-15 x 5-10 m (av. 10.8 x 7.4 pm), making apical blunt contact with the oogonium; antheridial stalks slightly swollen, of monoclinous or occasionally diclinous origin at a distance of 5-15 m, sometimes bearing short lateral hyphal elements. Oospores aplerotic or almost plerotic, (13-)22-27(-29) (av. 24) m diam, with a 1.5-3 m thick wall.

Cardinal temperatures: minimum 5C, optimum 20C, maximum <30C. Daily growth rate on potato-carrot agar at 25C: 4 mm.

Description based on CBS 315.81 and on the original description (sporangia). [p. 113]

Fig. 56. - P. okanoganense, CBS 315.81. a1-10. oogonia and antheridia. -b1-10. sporangia, in b4-7with discharge tubes, in b2-4sympodially, in b7-10 internally proliferating (reproduced, with permission, from Lipps, 1980). [p. 114]

Material examined

CBS 315.81 = ATCC 38595, type culture, isolated from rotten leaves of Triticum aestivum after melting of snow, USA, P. E. Lipps.

Discussion

P. okanoganense occasionally produces proliferating sporangia. In this way it differs from P. irregulare and P. ultimum. Moreover, P. irregulare has thinner oospore walls and in P. ultimum monoclinous antheridia always originate immediately below the oogonium. P. okanoganense is close to P. vexans which also rarely produces proliferating sporangia (Kouyeas and Theohari, 1977) but in P. okanoganense the antheridial cells are rounded towards the oogonial contact point and not bell-shaped as in P. vexans. The antheridial stalks of P. okanoganense are often somewhat inflated and the sporangia are larger than in P. vexans. Some other species with proliferating sporangia are easily distinguished from P. okanoganense: P. middletonii has mostly intercalary oogonia, P. marsipium and P. polytylum have larger oogonia and P. nagaii has thinner oospore walls and non-inflated antheridial stalks. Other species of Pythium described as causing snow rot, P. graminicola, P. paddicum and P. iwayamai, are different from P. okanoganense: P. graminicola has swollen filamentous sporangia, P. paddicum (invalid name) has ornamented oogonia, and P. iwayamai has often intercalary oogonia and forms rather thick-walled intercalary hyphal swellings.

Occurrence and pathogenicity

P. okanoganense is known from rotten leaves of Triticum aestivum, collected after melting of snow in the USA, and is considered to be the cause of snow rot (549a, 549b, 550a).

Fig. 57. - P. oligandrum, CBS 382.34. a1-3. oogonia, b1-2. sporangia [p. 115]

 

49. Pythium oligandrum Drechsler - Fig. 57, 6e, 7c.

Pythium oligandrum Drechsler - J. Wash. Acad. Sci. 20: 409. 1930; Phytopathology 36: 781-803.1946.

?Pythium amasculinum Y - Acta microbiol. sin. 13: 118. 1973 (cf. p. 186).

?Pythium sinense Y - Acta microbiol. sin. 13: 121. 1973 (cf. p. 196)

Colonies on cornmeal agar submerged, on potato-carrot agar without a special pattern. Main hyphae up to 7 m wide. Sporangia contiguous, forming irregular aggregates consisting of one or more subglobose elements with connecting filamentous parts, mostly intercalary, occasionally terminal. Zoospores formed at 18-20C. Discharge tubes 15-35(-200) m long. Encysted zoospores 9-10 m diam. Oogonia terminal or intercalary, sometimes lateral or unilaterally intercalary (17-)21-31(-35) (av. 25) m diam, provided with conical pointed protuberances; protuberances 5-7(-11) m long, 2-3 m diam at the base. Antheridia mostly lacking, but sometimes 1 or 2 per oogonium, diclinous, occasionally monoclinous, often adhering lengthwise to the oogonium, often with one or two transverse constrictions and appearing lobate. Oospores aplerotic, (14-)18-27(-33) (av. 22) m diam, wall 1-2.8 m thick.

Cardinal temperatures: minimum 7C, optimum 30C, maximum 37C. Daily growth rate on cornmeal agar at 25C: 30 mm.

Description based on CBS 382.34.

Material examined

CBS 382.34, isolated from Viola sp., England, C. G. C. Chesters, 1934. CBS 217.46, isolated from Viola sp., England, comm. C. J. Hickman, 1946. CBS 530.74 and 531.74, isolated from soil in Zuidelijk Flevoland, 1969, and roots of Linum usitatissimum, 1969, respectively, in the Netherlands, A. J. P.-N. IMI 120414, isolated from soil under lucerne, Ohio, USA, A. F. Schmitthenner, 1963.

Discussion

P. oligandrum typically has oogonia with long slender spines and complicated sporangial complexes; the latter consist of a number of irregular or subglobose units in mostly terminal clusters, forming either linear series or branched complexes. This kind of sporangium does not occur in other known species with ornamented oogonia.

In P. acanthicum the sporangia are rather irregularly shaped but less complicated than in P. oligandrum; in P. periplocum they are filamentous and inflated and clearly differ from those of P. oligandrum. In cultures on cornmeal agar abundant oogonia are soon produced giving the culture a yellowish and somewhat crustose appearance. The oogonial projections are longer and more slender than in P. periplocum and P. acanthicum. Most oogonia develop parthenogenetically but one or two antheridia may also be present on an oogonium, depending on the medium used and the temperature: irrigated lima-bean agar and a temperature of 18C favoured their production (221). The antheridial cells can be small and only slightly inflated but often they are long and, due to branching or constrictions, more or less lobate and closely applied to the oogonium.

P. sinense, originally isolated from soil in Peking, is possibly identical with P. oligandrum. Asexual and sexual elements are similar in both species. The only difference are the somewhat thicker oospore walls and slightly shorter ornamentations in P. sinense. [p.116]

Occurrence and pathogenicity

P. oligandrum was originally isolated from diseased peas near Eden, N.Y., USA. It has been recorded from soil and several plants in many countries, such as Daucus carota, Euphorbia pulcherrima, Rheum rhaponticum, Stipa sp. and Triticum aestivum (643) Medicago sativa (856), Phaseolus vulgaris and Lycopersicon esculentum (1088), all in the USA; it has been recorded in Argentina from Pisum sativum, Carthamus acutifolius, Pyrus malus and Santolina chamaecyparissus (291), in Queensland from Papaver (990), in Czechoslovakia from Beta vulgaris (1054), in England from Viola sp. (159, 160), in South Africa from Papaver and Antirrhinum (1066) and on Cyprus from Prunus amygdalus (700).

P. oligandrum is a rather common soil fungus occurring in various climates including tropical countries: Central Africa (515), South Australia (1038, 1039), Hawaii (502), the USA (368, 855), Germany (204), and the Netherlands (204, 743), where it was isolated particularly from cultivated soils.

P. oligandrum was found to be one of the Pythium species which cause crown-rot and damping-off of rhubarb, but was only weakly pathogenic for a number of Leguminosae tested (647, 648). It was only weakly or not at all pathogenic to sugar beet (1054, 1055 ), Papaver sp., Antirrhinum sp. (1066), barley, oat, and wheat (497), pineapple (502) and snapbeans (739).

On the other hand, P. oligandrum is an aggressive hyperparasite of other fungi: Pythium ultimum, P. debaryanum, and Aphanomyces laevis (1057), Phialophora radicicola, Botryotrichum piluliferum, Gaeumannomyces graminis and many Basidiomycetes (191). P. oligandrum overgrew the colonies of Streptomyces sp. and inhibited the growth of Rhizoctonia solani and Fusarium culmorum, Trichoderma viride and T. koningii (1058). Other fungi were resistant or even antagonistic to P. oligandrum (most Basidiomycetes tested). The susceptibility of fungi to P. oligandrum depends on the age of the hyphae, younger ones being more susceptible than older ones (192). P. oligandrum starts its infection on other fungi by entangling the hyphae of the host with thin haustorial branches, eventually leading to total destruction. In the presence of a host fungus, P. oligandrum produces abundant oogonia and germinating oospores, possibly due to sterols originating form lysed hyphae of the host. In the presence of resistant fungi no such profuse fructification was observed (191). The possibility of using P. oligandrum as a biological control agent against fungal diseases, e.g. Gaeumannomyces graminis, Pythium ultimum, has been considered (192, 1057, 1058, 1060).

 

50. Pythium orthogonon Ahrens - Fig. 58.

Pythium orthogonon Ahrens - Z. PflKrkh. PflSchutz 78: 177. 1971.

Colonies on cornmeal agar submerged, on potato-carrot agar with an indistinct radiate pattern. Main hyphae up to 5 m wide. Sporangia (sub)globose, non-proliferating, mostly terminal, rarely intercalary, 12-20 (av. 17) m diam; discharge tubes up to 6 m long. Zoospores 9-11 x 5-7 m. Oogonia formed at 25C on cornmeal agar, globose, [p. 117] but often including part of the oogonial stalk, terminal or unilaterally intercalary, 17-20(-21) (av. 18) m diam. Antheridia 1(-2) per oogonium, diclinous or monoclinous; antheridial cells 10-18 x 6-9 m, often crook-necked, evanescent after fertilization. Oospores plerotic, wall 1.5-3.0 m thick.

Fig. 58. - P. orthogonon, CBS 376.72. a1-9. oogonia and antheridia.

Cardinal temperatures: minimum 15C, optimum 30C, maximum about 40 C. Daily growth rate on potato-carrot agar at 25C: 12 mm.

Description based on CBS 376.72.

Material examined

CBS 376.72 = IMI 14351, type culture, isolated from Zea mays, Lebanon, C. Ahrens, 1969.

Discussion

Besides P. orthogonon, the group of Pythium species with globose, non-proliferating sporangia and plerotic oospores includes P. hypogynum, P. rostratum, P. tracheiphilum, P. salinum and P. pleroticum. P. hypogynum and P. rostratum have often hypogynous antheridia, which do not occur in P. orthogonon. P. tracheiphilum has larger sporangia and forms chlamydospores, P. salinum has only monoclinous antheridia and P. pleroticum has large hyphal swellings and 1-4 antheridia per oogonium. The rather high cardinal temperatures are also characteristic of P. orthogonon.

Occurrence and pathogenicity

Several isolations of P. orthogonon have been made from Zea mays in the Lebanon (10, 11). Other records of this fungus are not known. [p. 118]

Fig. 59. - P. ostracodes, CBS 768.73. al-6. oogonia and antheridia, b1-4. sporangia with proliferations.

[p. 119]

51. Pythium ostracodes Drechsler - Fig. 59.

Pythium ostracodes Drechsler - Phytopathology 33: 286. 1943.

Colonies on cornmeal agar forming profuse aerial mycelium, on potato-carrot agar a submerged Chrysanthemum pattern. Main hyphae up to 6 m wide. Sporangia terminal, proliferating, (sub)globose, 25-55 x 16-38 m; zoospores formed at 20 C; discharge tubes 2-45 x 4-9 m. New sporangia are occasionally produced on branches arising just below the primary sporangium. Encysted zoospores 10-12 m diam. Oogonia intercalary, unilaterally intercalary or terminal, smooth, (14-)35-38(-43) (av. 35) m diam. Antheridia 1-2 per oogonium, monoclinous, occasionally diclinous, with long antheridial cells often laterally applied to the oogonium along most of the length, 10-20 x 5-7 m. Oospores plerotic or nearly plerotic, but the wall never fused with the oogonial wall, (13-)30-34(-41) (av. 32.5) m diam, wall 4-5 m thick.

Cardinal temperatures: minimum over 10C, optimum 30C, maximum about 35C. Daily growth rate on potato-carrot agar at 25C: 8 mm.

Description based on CBS 768.73.

Material examined

CBS 768.73, isolated from soil, Ibiza, A. J. P.-N., 1972.

Discussion

The nearest congeners among the group with proliferating sporangia are P. oedochilum, P. palingenes and P. helicoides, all having thick-walled large oospores and large antheridia applied laterally to the oogonia. P. ostracodes differs from P. oedochilum and P. palingenes by its mostly monoclinous antheridia and plerotic or nearly plerotic oospores. It differs from P. helicoides by its antheridia which do not entwine the oogonial stalk. Hendrix and Papa (1974) placed P. ostracodes in one group with P. rostratum, P. fragariae, P. iwayamai, P. tracheiphilum, P. salpingophorum, P. salinum, P. orthogonon and P. pleroticum, because of their globose sporangia, terminal and intercalary smooth oogonia, and 1-2 mono- and diclinous antheridia per oogonium. As the proliferating nature of the sporangia is not always shown, they did not consider proliferation as a useful taxonomic character.

CBS 768.73 fits Drechslers description in most characters but differs in a few respects, viz. the oospores are nearly plerotic, but there is always some space between the oogonial and the oospore wall; the antheridia are often diclinous and more like those of P. oedochilum. On the other hand, the colony pattern and growth rate differ from those of P. oedochilum but are more in agreement with P. ostracodes.

Occurrence and pathogenicity

P. ostracodes was originally isolated from wheat in Texas. Subsequently it has rarely been reported, It has been isolated from rhizomes of lotus in Japan (980). [p. 120]

Fig. 60. - P. palingenes. a1-3. oogonia and antheridia, b1-3. various types of succession of proliferating sporangia, c. vesicle with zoospores (reproduced, with permission, from Drechsler, 1941).

[p. 121]

52. Pythium palingenes Drechsler - Fig. 60.

Pythium palingenes Drechsler-J. Wash. Acad. Sci. 20: 416.1930; Phytopathology 31: 486-492. 1941.

Main hyphae up to 7 m wide. Appressoria often present. Sporangia terminal, subglobose or ovoid, 24-42 x 18-33 (av. 33 x 29) m, papillate, proliferating or forming secondary sporangia on branches originating just below the septum of the primary one, discharge tubes 2-35 (av. 8) m long and 5.5-10 (av. 6.5) m wide, mostly arising from the apex, occasionally from other parts; encysted zoospores 11-17 (av. 14) m diam. Oogonia terminal, sessile, intercalary or unilaterally intercalary, subglobose, (19-)28-40(-41) (av. 34) m diam, wall 0.4-1.0 m thick. Antheridia (1-)2(-4) per oogonium, diclinous; antheridial stalks and also vegetative hyphae wrapping around the oogonial stalk in a few turns; antheridial cells cylindrical, often wavy or irregular in contour, 10-28 x 6-8 m, applied lengthwise to the oogonium over its entire length or along its anterior portion. Oospores yellowish, subglobose, aplerotic, (18-)26-36(-37) (av. 31.3) m diam, wall 1.5-3.5 (av. 2.6) m thick.

No material available.

Discussion

P. palingenes is very close to P. oedochilum, but differs from it by its predominantly intercalary or lateral oogonia.

Occurrence and pathogenicity

P. palingenes was originally isolated from discoloured roots of Ambrosia trifida near Delaplane, USA, and later from discoloured roots of Senecio jacobaea (218). Nothing is known about its pathogenicity.

 

53. Pythium papillatum Matthews - Fig. 61.

Pythium papillatum Matthews - J. Elisha Mitchell scient. Soc. 43: 231. 1928.

Main hyphae irregular, mostly up to 10(-24) m wide, forming bud-like outgrowths in old cultures. Sporangia filamentous, non-inflated, branched or unbranched. Zoospores up to 20 or more in a vesicle, 12 x 7.2 m, after encystment about 12m diam. Oogonia terminal on short branches or intercalary, often catenulate, globose to oval, smooth or with 1 or 3 papillae, 16.5-26.5 m diam. Antheridia lacking. Oospores plerotic.

No material available. [p. 122]

Fig. 61. - P. papillatum. al-7. oogonia, a5-6 with spines, a7 with two oospores; b1. filamentous sporangium forming a vesicle, b2. zoospores in vesicle, c1-2. free and encysted zoospores (redrawn from Matthews, 1928).

Discussion

P. papillatum may be distinguished from the related P. monospermum and P. marinum by the presence of oogonial projections, the occurrence of catenulate oogonia and the lack of antheridia.

Occurrence and pathogenicity

P. papillatum was originally isolated from soil in the USA. Other records come from Hordeum vulgare in the USA (643) and water in the USSR (635). [p. 123]

 

54. Pythium paroecandrum Drechsler - Fig. 62.

Pythium paroecandrum Drechsler - J. Wash. Acad. Sci. 20: 406. 1930; Phytopathology 30: 202-212.1940.

Colonies on cornmeal agar submerged, on potato-carrot agar showing a radiate pattern. Main hyphae up to 9 m wide. Appressoria often present. Sporangia (sub)globose or ellipsoidal, intercalary or terminal, 12-33 m diam; discharge tubes 4-20(-100) m long and about 4 m wide, sometimes widening at the tip. Oogonia (sub)globose, mostly intercalary, often in chains, rarely terminal, smooth, (14-)17-24 (-27) (av. 19) m diam. Antheridia 1-2(-5) per oogonium, monoclinous, sometimes sessile, diclinous, occasionally intercalary or hypogynous. Oospores aplerotic, smoothwalled, (13-)15-21(-23) (av. 17) m diam, wall 1.0-1.5 m thick.

Cardinal temperatures: minimum 5C, optimum 25C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 20-25 mm.

Description based on CBS 157.64.

Material examined

CBS 157.64, isolated from loamy nursery soil, Adelaide, Australia, O. Vaartaja, 1962. CBS 203.79, isolated from water near Utrecht, Netherlands, A.J.P.-N., 1967. CBS 651.79, isolated from soil near Glane, and CBS 204.79, near Zutphen, Netherlands, A.J.P.-N., 1965. IMI 48560, slide of culture isolated from unknown substrate, and many other isolates not maintained in the CBS collection.

Discussion

Characteristic of this species is the variability of the antheridia. They can be monoclinous, sessile or originate from the oogonial stalk near the oogonium; sometimes two antheridia are arranged in a series, the second one formed on an outgrowth of the first one; but also diclinous antheridia occur, either terminal on an antheridial stalk or intercalary on a neighbouring hypha, the part of the oogonial branch adjacent to the oogonium can also form a hypogynous antheridium. Though all these kinds of antheridia were present in the isolates studied, in some cases some monoclinous antheridia were present which originated at some distance from the oogonium. This was also shown in Middletons drawings (1943) but not mentioned in Drechslers diagnosis. The sporangia in P. paroecandrum are larger than the oogonia, often intercalary, and sometimes comprise part of the sporangial hypha, from which discharge tubes often arise, but these can also be formed from any other part of the sporangium.

P. paroecandrum is related to P. irregulare but differs from it by the more regular and slightly larger, mostly intercalary oogonia which also lack the typical finger-like projections; moreover, in P. irregulare no intercalary antheridia occur. These also lack in P. ultimum, which in addition has thick-walled oospores. P. paroecandrum differs from P. salpingophorum and P. rostratum by its aplerotic oospores. [p. 124]

Fig. 62. - P. paroecandrum, CBS 157.64. al-4. oogonia and antheridia, b1-3. appressoria.- d l-4. sporangia, d 4 discharging, e. chain of oogonia (reproduced, with permission, from Drechsler, 1940).

[p. 125]

Occurrence and pathogenicity

P. paroecandrum was originally isolated from Allium vineale in the USA (211, 217). It is not very common but widely distributed. It has been recorded in the USA from Alo sp. (643), peach seedlings (664), alfalfa (856), Chrysanthemum sp. (568), roots of diseased peach (376) and carrot (654); in Australia from wheat (544), in Czechoslovakia from Cactus (147), in the Netherlands from flower bulbs and Antirrhinum (743), and in Ireland from tulips (521). It has often been isolated from soil: In the USA (125, 368, 371), Germany (859), Australia (1039), Lebanon (11), the Netherlands (743), and also from water (743).

In inoculation experiments P. paroecandrum was weakly pathogenic to seedlings of a number of Phanerogams: clover (338, 339), peach (664), alfalfa (856), Chrysanthemum sp. (568), Pinus sp. (364), carrot (654) and maize (409). P. paroecandrum was most pathogenic at 28C in contrast to P. ultimum which caused most damage at 23.5C (568).

 

 

55. Pythium periilum Drechsler - Fig. 63.

Pythium periilum Drechsler - J. Wash. Acad. Sci. 20: 403. 1930; Phytopathology 30: 198. 1940.

Colonies on cornmeal agar submerged, on potato-carrot agar with a radiate pattern. Main hyphae up to 6 m wide. Appressoria subspherical. Sporangia partly strictly filamentous, partly consisting of inflated elements, 16-20 m wide. Zoospores formed at 20C. Oogonia terminal or intercalary, smooth, globose, but often including part of the oogonial stalk, (17-)18-21(-23) (av. 20.0) m diam. Antheridia 2-5 per oogonium, monoclinous or diclinous, stalks branched, bearing 1-5 antheridial cells and vegetative prolongations entangling the oogonium and the oogonial stalk; antheridial cells crook-necked, 7-14 x 4-5 m, making apical contact with the oogonium. Oospores colourless or slightly yellowish, smooth, plerotic or nearly so, wall 1.0-2.0 m thick.

Cardinal temperatures: minimum about 10C, optimum 30C, maximum 40C. Daily growth rate on potato-carrot agar at 25C: 13 mm.

Description based on CBS 169.68. [p. 126]

Fig. 63. - P. periilum, CBS 169.68. a l-5. oogonia and antheridia, b l-6. toruloid sporangia, C l-2. encysted and c 3. germinating zoospores, d l-2. appressoria.

[p. 127]

Material examined

CBS 169.68 = IMI 120405, isolated from soil, Florida, A. F. Schmitthenner, 1962; comm. G. M. Waterhouse, 1968. CBS 218.80, isolated from soil, India, A. J. P.-N., 1971.

Discussion

According to Drechsler the sporangial system consists of a combination of inflated and non-inflated elements, a situation which is sometimes also found in species such as P. torulosum and P. myriotylum. The first-formed sporangia are often strictly filamentous, but after a period of time typical complexes of the inflated parts appear in water cultures. P. periilum differs from P. torulosum by its complicated antheridial system and from P. myriotylum by its plerotic oospores.

Occurrence and pathogenicity

P. periilum was originally collected by Rands and Dopp from diseased roots of Saccharum officinarum in the USA in 1927 and was reported there again on sugar-cane (784, 789, 954) and once from Elytrigia repens (267). It has also been reported in Queensland from sugar-cane and Medicago sativa (991). It is considered a weak wound parasite of sugar-cane (789).

Fig. 64. - P. periplocum, CBS 289.31. a l-4. oogonia, b l-2. sporangia.

 

56. Pythium periplocum Drechsler -Fig. 64, 7b.

Pythium periplocum Drechsler - J. Wash. Acad. Sci. 20: 405, 1930; Phytopathology 29: 402 408. 1939.

Pythium periplocum var. coimbatorense Balakrishnan - Proc. Ind. Acad. Sci., Sect. B, 28: 31. 1948 (nom. inval. Art. 36, 37). [p. 128]

Colonies on cornmeal and potato-carrot agars producing only scanty aerial mycelium, on potato-carrot agar without a special pattern. Main hyphae up to 9 m wide. Sporangia terminal and intercalary, consisting of branched, lobulate or digitate elements forming large complexes. Discharge tubes often very long, occasionally up to 500 m. Encysted zoospores 8-11 m diam. Oogonia terminal and intercalary, (19-)24-27(-29) (av. 26) m diam, ornamented with blunt spines; spines 2-4(-5) m long and 1.5-3 m diam at the base. Antheridia 1-4 per oogonium, diclinous, occasionally clavate, mostly up to 30 m long, lobate or branched, closely applied to and often more or less entangling the oogonium. Oospores aplerotic, (sub)globose, (18-)20-24(-26) (av. 22) m diam, wall up to 3 m thick.

Cardinal temperatures: minimum 5-10C, optimum 30C, maximum 40C. Daily growth rate on potato-carrot agar at 25C: 35 mm.

Description based on CBS 289.31.

Material examined

CBS 289.31, type cutture, isolated from Citrullus vulgaris, USA, C. Drechsler, 1930, comm. T. S. F., Ashby, 1931. CBS 170.68 = IMI 120418, isolated from soil under sugar cane, Louisiana, USA, A. F. Schmitthenner, 1964, comm. G. M. Waterhouse, 1968. CBS 532.74, isolated from soil, Oostelijk Flevoland, Netherlands, A. J. P.-N., 1971.

Discussion

P. periplocum is the only known species with ornamented oogonia and filamentous inflated sporangia. The sporangia are formed abundantly both in water and agar cultures. The oogonia often degenerate before oospores are formed.

The variety coimbatorense, isolated from vegetable debris in water in India, is said to differ from var. periplocum by possessing asexual resting spores in ageing cultures, and larger oogonia and oospores.

Occurrence and pathogenicity

P. periplocum was originally isolated in the USA from Citrullus vulgaris. Later it was again recorded in the USA from C. vulgaris (783), Cucumis melo (643) and Prunus serotina (215), in Argentina from Phoenix dactylifera (291), in Brasil from Cineraria sp. (141) and in the Anglo-Egyptian Sudan from cotton (22). Also some records from soil are known in the USA (368) and the Netherlands (743).

Little is known about its pathogenicity. It may cause cotton wilt (22, 610) and blossom end-rot of Citrullus vulgaris (211, 215).

57. Pythium perniciosum Serbinow - Fig. 65.

Pythium perniciosum Serbinow - Bot. Oboz. 28: 29. 1912 (Scripts bot. Hort. Univ. Petrop.) Nematosporangium perniciosum (Serbinow) Jaczewski - Opredelitel Griboy I, Fikomitsety, p. 97. 1931. [p. 129]

Fig. 65. - P. perniciosum. a l-3. oogonia, in a l with antheridium, b. sporangium, c. catenulate hyphal swellings, d. inflated portion of a hypha (redrawn from Serbinow, 1912; magnification not indicated).

Main hyphae up to 9.5 m wide, forming catenulate, globose or irregular hyphal swellings (oidia) which are easily shed. Sporangia filamentous, non-inflated, arising from mycelial branches or from sac-like cells, always separated from the supporting part of the mycelium by a cross-wall. Encysted zoospores 8-12 m diam. Oogonia terminal on short side branches, 19-39 m diam, smooth. Antheridia 1-2 per oogonium, mono- or diclinous, variable in shape, straight or curved. Oospores aplerotic, often irregularly angular, smooth, 18-23.5 m diam, thick-walled.

Cardinal temperatures: minimum 4C, optimum 18-31C, maximum 37C. Daily growth rate on cornmeal agar at 25C: 16 mm.

No material available.

Discussion

P. perniciosum may be distinguished from other species with filamentous sporangia and aplerotic thick-walled oospores by its catenulate hyphal swellings. Drechsler (1929) doubted the purity of Serbinows isolates because of the occurrence of both filamentous and sac-like sporangial elements, but Middleton (1943) assured that he worked with pure cultures which conformed with Serbinows description in all respects.

Occurrence and pathogenicity

P. perniciosum has been recorded from tobacco seedlings in the USSR (250, 874), Viola tricolor in the Netherlands (240), Hibiscus sp. in Indonesia (685), and Poinsettia (643, 1018) and strawberry in the USA (703, 704, 705). In all cases it was pathogenic to the hosts. Moreover, Serbinow proved in inoculation experiments its pathogenicity to species of Amaranthus, Antropa, Barbarea, Brassica, Camelina, Chenopodium, Linum, Lycopersicon, Sinapis, Solanum, Thlaspi and some ferns (874).

 

58. Pythium perplexum Kouyeas & Theohari - Fig. 66.

Pythium perplexum Kouyeas & Theohari - Annls Inst. Phytopath. Benaki 11: 282. 1977.

Colonies showing a radiate to indistinct rosette pattern. Sporangia variously shaped, terminal or intercalary, occasionally in series, 8-36 (av. 17) m diam. Encysted [p. 130] zoospores 8-10.5 (av. 9.3) m diam. Oogonia globose, smooth, terminal on lateral branches, 17-30 (av. 23.5) m diam, often attached by a broad base. Antheridia 1(-2) per oogonium, usually monoclinous, originating at a short distance from the oogonium. Antheridial cells making broad contact with the oogonium, bell-shaped. Oospores aplerotic, 15-25 (av. 21) m diam, straw-coloured with a 1.5-1.7 m thick wall.

Fig. 66. - P. perplexum, a l-5. oogonia and antheridia, b. sporangia (reproduced, with permission, from Kouyeas and Theohari, 1977).

Cardinal temperatures: minimum below 4C, optimum 22C, maximum below 32C. Daily growth rate on cornmeal agar at 25C: 12-13 mm.

No material available. [p. 131]

Discussion

Kouyeas and Theohari (1977) concluded that the species described by Butler (1907) as P. vexans was different from P. vexans described by de Bary (1876). The Greek isolates were similar to Butlers species except in that they lacked the hypogynous antheridia mentioned by Butler. Middleton (1943) probably confused the two species in his treatise of P. vexans. Kouyeas and Theohari (1977) agreed with the synonymy of P. piperinum, P. ascophallon and P. complectens with P. vexans. P. perplexum differs from P. vexans by its larger oogonia and oospores, non-proliferating sporangia, a lack of lobed antheridia and by other temperature-growth relationships. In isolates identified as P. vexans, as well in a culture of Dasturs P. piperinum, CBS 334.36, Kouyeas and Theohari (1977) obtained proliferating sporangia. Proliferating sporangia had not been noticed before in P. vexans.

Occurrence and pathogenicity

P. perplexum was originally isolated from Medicago sativa and Humulus lupulus and soil in Greece. Besides Kouyeas and Theoharis Greek isolates, P. perplexum has possibly been recorded as P. vexans from soil in Ireland, England and France (120). No investigations into its pathogenicity are known.

 

59. Pythium polymastum Drechsler - Fig. 67.

Pythium polymastum Drechsler - J. Wash. Acad. Sci. 20: 412. 1930; Phytopathology 29: 1011. 1939.

Colonies on cornmeal agar showing some low, floccose aerial mycelium, on potato-carrot agar no special pattern. Main hyphae up to 9 m wide. Sporangia subglobose, often oblate, ellipsoidal or irregularly shaped, (21-)27-40(-48) (av. 34.5) m diam, intercalary or terminal. Zoospores formed at 15-18C. Discharge tubes arising from any part of the sporangium, mostly 16-100(-180) m long and 5-6 m wide. Oogonia mostly terminal on short side branches, (sub)globose, (24-)30-64(-69) (av. 53) m diam, provided with heavy spines; protuberances conical or mammiform, 5(-8) m long and 5-6 m diam at the base. Antheridia 1-4 per oogonium, diclinous, variously shaped, terminal or intercalary, 20-43 x 12-21 m, lobate or with hyphal or diverticulate projections; antheridial cells making broad apical contact with the oogonium, one antheridium often entangling the stalk and basal part of the oogonium. Oospores aplerotic, (20-)28-51(-56) (av. 43.5) m diam, wall 2-5 m thick.

Cardinal temperatures: minimum about 5C, optimum about 25C, maximum about 30C. Daily growth rate on potato-carrot agar at 25C: 24 mm.

Description based on CBS 811.70.

Material examined

CBS 810.70 and 811.70, isotated from Lactuca sativa, Wageningen, J. H. yan Emden, 1969. Slide IMI 6287, isolated from stockroots, England, J. Ives. [p. 132]

 

 

 

 

 

 

 

Fig. 67. - P. polymastum, CBS 811.70. a l-9. oogonia and antheridia. b l-4. sporangia, some with discharge tubes, c. hyphal swelling. - d. young, and e. mature oogonia and antheridia (d and e reproduced, with permission, from Drechsler, 1939) (long bar for a 5, a l, a 8, short bar for remaining drawings).

[p. 133]

Discussion

Both CBS isolates differ slightly from the original description in having larger oogonia and oospores (originally given 27-67, av. 45.6, and 25-42, av. 35.3 m, respectively). Mammiform ornamentations on the oogonia are only found in P. polymastum and P. mastophorum. Of these two species, P. polymastum has larger oogonia and the sporangia are usually intercalary, while they are terminal in P. mastophorum.

Occurrence and pathogenicity

P. polymastum was originally isolated from Lactuca sativa in Connecticut, USA, subsequently recorded again in the USA from Bellis perennis, Daucus carota and Euphorbia pulcherrima (643) and in the Netherlands from L. sativa (743). Vanterpool (1046) isolated a fungus from Brassica campestris, B. napus, Capsella bursa-pastoris and Lunaria annua in Canada, which he identified as P. polymastum. His fungus differed slightly from Drechslers in having conical rather than mammiform ornamentations. These isolates were typical pathogens of crucifers of which 18 species were tested, but they were not or only slightly pathogenic to many other cultivated plants of other families. P. polymastum has also been shown to be pathogenic to cabbage (845).

Fig. 68. - P. polypapillatum. a l-3. oogonia and antheridia, in a 2 hypogynous, b l-4, discharging and proliferating sporangia (redrawn from Ito, 1944).

 

60. Pythium polypapillatum T. Ito - Fig. 68.

Pythium polypapillatum T. Ito - J. Jap. Bot. 20: 58. 1944

 

 

Main hyphae up to 8.5 m wide. Sporangia globose, ovoid or pyriform, terminal, 25-35 x 23-30 m, proliferating. Zoospores 13-16 x 11-13 m. Oogonia terminal, subglobose, 16.5-28 m diam, ornamented; projections on young oogonia conical, on mature oogonia cylindrical, blunt, sometimes widening at the tip or branching dichotomously, [p. 134] 5-26 m diam at the base. Antheridia mono- and diclinous, rarely hypogynous, 1-4 per oogonium, clavate or elongate. Oospores aplerotic, 11.5-21.5 m diam.

No material available.

Discussion

Among the species with ornamented oogonia and proliferating sporangia, P. paddicum, P. echinulatum, P. irregulare, P. hydnosporum and P. acanthophorum have sporangia smaller than 35 m in average diameter, but all these species have an ornamentation which at maturity clearly differs from that of P. polypapillatum. None of the other species has branched ornamentation. P. polypapillatum is only known from the original description from water in Japan (442) and the USSR (635).

 

61. Pythium polytylum Drechsler

Pythium polytylum Drechsler - J. Wash. Acad. Sci. 20: 415. 1930.

Main hyphae up to 8 m wide. Sporangia sometimes intercalary, unilaterally intercalary, but usually terminal, sometimes internally proliferating but mostly forming secondary sporangia on short branches immediately below the primary sporangium. Primary sporangia subglobose. 28-33 m diam, sometimes papillate; discharge tubes 8-20 x 7-9 m, arising mostly from the apex but occasionally from other parts; encysted zoospores 9.5-11.5 m diam. Oogonia smooth, terminal or lateral and sessile, (26-)29-37(-40) (av. 32.5) m diam. Antheridia 1(-4) per oogonium, borne terminally, diclinous, occasionally monoclinous; antheridial cells curved, elongate cylindrical, often somewhat wavy in contour, 15-40 x 5-7.5 m (av. 30 x 6 m), applied lengthwise to the oogonium. Oospores aplerotic, yellowish, subglobose, (23-)25-33(-35) (av. 28.8) m diam, wall 2.1-3.4 (av. 2.5) m thick.

No material available

Discussion

P. polytylum differs from P. ostracodes by its aplerotic oospores, from P. helicoides, P. oedochilum and P. palingenes by its always globose sporangia.

Occurrence and pathogenicity

P. polytylum was originally isolated from decaying roots of Prunella vulgaris in the USA, subsequently from Spinacia oleracea (643) and Chrysanthemum morifolium (568) in which it could cause severe stem- and root-rot. A high soil moisture and temperatures above 11.5C favoured disease. [p. 135]

Fig. 69. - P. porphyrae. a1-5. oogonia with l-4 antheridia, b. sporangium releasing a zoospore vesicle, c1-4. hyphal swellings (reproduced, with permission, from Takahashi et al., 1977).

 

62. Pythium porphyrae Takahashi & Sasaki - Fig. 69.

Pythium porphyrae Takahashi & Sasaki - Trans. mycol. Soc. Japan 18: 280. 1977.

Colonies on cornmeal-seawater agar showing some low aerial mycelium, on potato-carrot agar not growing. Main hyphae up to 4.5 m wide. Sporangia filamentous, non-inflated, unbranched, forming 6-17 zoospores in a vesicle at 25 C. Oogonia 14.5-19.5 m diam, globose, intercalary, rarely terminal. Antheridia 1-2(-4) per oogonium, diclinous, arising from points far from the oogonial stalk; occasionally two antheridial cells formed on one stalk; antheridial cells globose or clavate. Oospores plerotic, 13.2-17.5 m diam, thick-walled. [p. 136]

Cardinal temperatures: minimum 15C, optimum 30C, maximum 35C. Daily growth rate on seawater-cornmeal agar at 25C: 5 mm.

Material examined

CBS 359.79, isolated from Porphyra yezoensis, Japan, T. Yoshida, 1967.

Discussion

P. porphyrae is similar to P. monospermum and P. marinum in its filamentous, non-inflated sporangia, plerotic, thick-walled oospores and size of the oogonia and oospores. However, it has 1-2(-4) diclinous antheridia and occasionally 2 antheridial cells originating from one stalk, while P. monospermum has 1-4 mono- or diclinous antheridia. In P. marinum only one diclinous antheridium is present. In P. marinum and P. monospermum the oogonia are formed terminally on short side branches but in P. porphyrae they are mostly intercalary. The isolate CBS 359.79 does not sporulate. The description is derived from the original text.

Occurrence and pathogenicity

Arasaki (33, 34, 35) reported a fungal disease of Porphyra tenera in Japan, but a description and taxonomic study of the causal organism was not made until 1977. P. porphyrae, the causal agent of red rot of Porphyra species, was recorded and described in other papers before a diagnosis was published (833, 843, 974). Further studies about its physiology followed (292, 293, 294). Till now it has not been recorded from other countries.

 

63. Pythium prolatum Hendrix & Campbell - Fig. 70.

Pythium prolatum Hendrix & Campbell - Mycologia 61: 387-388. 1969.

Colonies on cornmeal agar submerged, on potato-carrot agar showing a radiate pattern. Main hyphae up to 7 m wide. Sporangia ovoid, elongate, often distorted or irregularly shaped, with beaked or hypha-like outgrowths, rarely proliferous, up to 100(-120) m long and 20-40 m wide. Oogonia terminal, 17-33 (av. 26) m diam, ornamented with conical, blunt, sometimes more or less mammiform protuberances which are 4-8 m long, have a broad base, and densely cover the oogonium. Antheridia diclinous, 1(-2) per oogonium, irregularly shaped; stalks often with side branches forming a tangled mass of hyphae; antheridial cells inflated, making broad, lengthwise contact with the oogonium. Oospores definitely aplerotic, (16-)17-28(-31) (av. 24) m diam, wall 1.5-3.0 m thick.

Cardinal temperatures: minimum 5C, optimum 25C, maximum above 35C . Daily growth rate on potato-carrot agar at 25C: 20-24 mm.

Description based on CBS 845.68. [p. 137]

Fig. 70. - P. prolatum, CBS 845.68. a1-6. oogonia and antheridia, b1-4. elongate sporangia.

[p. 138]

Material examined

CBS 845.68, type culture, and 844.68, isolated from soil under Rhododendron sp. and Cleyera sp., respectively, Georgia, USA, F. F. Hendrix Jr. and W. A. Campbell, 1968.

Discussion

P. prolatum, P. anandrum and P. megalacanthum form a group of species with ornamented oogonia and proliferating sporangia. P. prolatum differs from P. anandrum in the shape of the ornamentation which in P. prolatum densely covers the oogonia; in P. anandrum the ornamentation is more widely spaced so that the oospore can clearly be seen. In P. anandrum the spines are conical and not mammiform, have a smaller base and a longer, slimmer upper part than in P. prolatum. In P. anandrum the sporangia are more regular and not so contorted as in P. prolatum while antheridia are mostly lacking. P. prolatum differs from P. megalacanthum by its smaller oogonia and oospores, much denser ornamentation of the oogonium and thicker oogonial wall.

Occurrence and pathogenicity

P. prolatum was originally isolated from soils under Rhododendron, Camellia and Cleyera in Georgia, USA. So far no other records are known.

Fig. 71. - P. pulchrum. a1-4. oogonia, b1-4. discharging and emptied sporangia (redrawn from Minden, 1916; magnification not indicated).

[p. 139]

 

64. Pythium pulchrum Minden - Fig. 71.

Pythium pulchrum Minden - Mykol. UntersBer. 1: 227. 1916.

Pythium epigynum Hhnk - Mycologia 24: 505. 1932.

Main hyphae up to 7 m wide. Sporangia globose, pyriform or ellipsoidal, occasionally catenulate or bunched together through lateral outgrowths, 24-48 (av. 38) m diam, collapsing after discharge; discharge tubes short. Zoospores up to 25 or more in a vesicle, 14-16 x 9m, becoming 11-16m diam after encystment. Oogonia terminal, mostly intercalary, globose, occasionally 2-5 in a series, smooth, 19-38 (av. 28) m diam. Antheridia mono- or diclinous, but mostly hypogynous, 1-2 per oogonium; monoclinous antheridia often sessile or short stalked. Oospores aplerotic, 14-31 (av. 24.5) m diam, wall moderately thick.

No material available.

Discussion

P. pulchrum differs from other species with non-proliferating globose sporangia and aplerotic oospores in having catenulate sporangia. Various proportions of hypogynous antheridia also occur in other species in this group. These include P. ultimum, occasionally P. paroecandrum, P. rostratum and, particularly, P. hypogynum, though the latter two species have plerotic oospores.

P. epigynum is not sufficiently different from P. pulchrum to recognize it as a separate species. In P. epigynum no stalked antheridia are described, while in P. pulchrum the ratio stalked and non-stalked antheridia is variable. Matthews (1931) mentioned the occurrence of two oospores in one oogonium, which is also illustrated by Hhnk (1956) for P. epigynum.

Occurrence and pathogenicity

P. pulchrum was originally isolated from ant pupae in bog water in Hamburg, Germany. It has been recorded mostly from soil: In the USA (368,402, 639, 865), Iraq (13), C zechoslovakia (147), Brasil (141), other South-American countries (63) and Iceland (469); from roots and soil in Taiwan (424) and from water in Germany (402) and the USSR (634, 635). The few records from plants include ones from alfalfa (108), Antirrhinum sp., Callistephus sinensis, Persea americana (643) and pear trees (928) in the USA and sugar-cane roots in Japan (1082). Nothing is known about its pathogenicity, but Hhnk (399) could recover his isolate of P. epigynum after inoculation of grasses.

 

65. Pythium pyrilobum Vaartaja - Fig. 72.

Pythium pyrilobum Vaartaja - Mycologia 57: 425. 1965.

Colonies on cornmeal agar submerged, on potato-carrot agar without a special pattern. Main hyphae up to 12 m wide. Large clavate appressoria occasionally present. [p. 140]


Fig. 72. - P. pyrilobum, CBS 158.64. a1-7. oogonia and antheridia, lower magnification, b1-47. sporangia, C1-2. encysted zoospores, d1-2. appressoria, higher magnification.

[p. 141] Sporangia consisting of globose, pyriform and filamentous elements with occasionally irregularly inflated parts, intercalary, contiguous; discharge tubes arising from either the swollen globose to pyriform or the filamentous parts, up to 200 m long and 6 m wide; vesicles 20-60 m diam, containing up to 35 zoospores; zoospores large, 14-20 x 10-16 m, after encystment 14 m diam. Oogonia globose or pyriform, terminal or intercalary, (23-)25-28(-33) (av. 27) m diam. Antheridia 1-8 per oogonium, diclinous and monoclinous, mostly 2 or 3 cells on one long stalk which encircles the oogonium; antheridial cells 8-12 x 5-6 m, mostly crook-necked, making apical, occasionally lateral contact with the oogonium. Oospores aplerotic and plerotic, yellow, (20-)21-25(-32) (av. 23.5) m diam, wall 1.7-4 m thick.

Cardinal temperatures: minimum 4C, optimum 25C, maximum 37C. Daily growth rate on potato-carrot agar at 25C: 22 mm.

Description based on CBS 158.64.

Material examined

CBS 158.64 = ATCC 16516, type culture, isolated from Pinus radiata seedling, S. Australia, O. Vaartaja, 1961.

Discussion

P. pyrilobum is distinct by the compound sporangia and smooth oogonia. P. oligandrum and P. acanthicum also have contiguous sporangia but form ornamented oogonia. The sexual organs of P. pyrilobum are rather similar to species such as P. aristosporum, P. tardicrescens, P. myriotylum and P. scleroteichum. The sporangia of the first three species are lobate and clearly different from those of P. pyrilobum. Sporangia of P. scleroteichum have never been observed. P. pyrilobum grows faster than P. tardicrescens and has slightly lower cardinal temperatures than P. scleroteichum.

There have been no other records of P. pyrilobum since the original isolation from pine seedlings in S. Australia.

 

66. Pythium pythioides (Roze & Cornu) Ramsbottom - Fig. 73.

Cystosiphon pythioides Rose & Cornu - Annls Sci. nat., Bot., Sr. 5, 11: 73-81. 1869 (reproduced in Bibl. Ec. haut. Etud. Sci. nat. 2: 2-11. 1870) = Pythium cystosiphon Lindstedt - Synopsis der Saprolagniaceen and Beobachtungen ber einige Arten. Diss. Berlin, p. 50. 1872 = Pythium pythioides (Roze & Cornu) Ramsbottom - Trans. Br. mycol. Soc. 5: 315. 1916.

Zoosporangia formed in the cells of aquatic floating plants, globose or more or less elongate, 20 m diam; discharge tubes piercing through the host cell walls; zoospores irregularly reniform, 8-16 m long. Oogonia terminal, subterminal or intercalary, smooth, 13-24 m diam. Antheridia diclinous, 1-3 per oogonium, crook-necked, terminal, making apical contact. Oospores aplerotic with a reticulate thick wall.

No material available. [p. 142]

Fig. 73. - P. pythioides. a1-2. oogonia and antheridia, b. sporangium with beginning discharge of zoospores (redrawn from Roze & Cornu, 1869).

Discussion

This species was originally observed in Wolffia michelii, Lemna minor, L. gibba and Riccia fluitans in France. It is easily distinguished from all other known species of Pythium by its reticulate oospores. No other records of P. pythioides are known.

 

67. Pythium rostratum Butler - Fig. 74, 2c.

Pythium rostratum Butler - Mem. Dep. Agric. India, bot Ser. 1: 84. 1907.

Pythium diameson Sideris - Mycologia 24: 47. 1932.

Colonies on cornmeal agar submerged, on potato-carrot agar showing a Chrysanthemum pattern (Fig. 2c). Main hyphae up to 8 m wide. Sporangia globose, ovoid, limoniform or ellipsoidal, non-proliferating, terminal or intercalary, (17-)19-32 (av. 25) m diam when globose, up to 27 x 23 m when oblong; zoospores formed at 25C; discharge tubes of varying length and about 5 m wide. Oogonia smooth, (sub)globose, mostly intercalary, occasionally terminal, (17-)19-24(-26) (av. 21.5) m diam, often in chains. Antheridia 1-2 per oogonium, monoclinous, mostly sessile and arising immediately below the oogonium or hypogynous. Oospores plerotic or nearly so, wall about 2 m thick.

Cardinal temperatures: minimum below 5C, optimum 25C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 8 mm.

Description based on CBS 533.74 which is proposed as neotype culture.

Material examined

CBS 383.34, isolated from leaf litter, Netherlands, F. Tjallingii, 1933. CBS 172.68 = IMI 120413, isolated from roots of Medicago sativa, comm. G. M. Waterhouse. CBS 533.74, neotype culture, and 534.74, isolated from soil and water respectively, Netherlands, A. J. P.-N., 1971;and several other isolates not maintained in the CBS collection. [p. 143]

Fig. 74. - P. rostratum, CBS 533.74. a1-7. oogonia and antheridia, b1-5. sporangia with short discharge tubes.

Discussion

Characteristic of this slow-growing species are the intercalary often catenulate oogonia and monoclinous, sessile or hypogynous antheridia. Only few species in the group of species with globose, non-proliferating sporangia have hypogynous antheridia, viz. P. hypogynum, P. pulchrum and, occasionally, P. ultimum (incl. its var. sporangiiferum). P. rostratum can easily be distinguished from P. pulchrum and both varieties of P. ultimum by its plerotic oospores. P. hypogynum is distinguished from P. rostratum by the mainly hypogynous antheridia and mostly terminal oogonia.

P. diameson is very similar to P. rostratum, as stated already by Middleton (1943) and can be placed in synonymy with it. The doubtful species P. plerosporon Sideris (1932) is described as being similar to P. rostratum except in the smaller oogonia and oospores; its growth rate (Middleton, 1943) is also much faster than that of P. rostratum. An identification of P. plerosporon is not possible.

Occurrence and pathogenicity

P. rostratum was originally isolated from garden soil in France. It is a typical soil fungus. In the Netherlands it was often found in wet, dry and even very dry soils, near birds nests or rabbits burrows and in water (743). It has been recorded from soil in the [p. 144] USA (126, 368, 372, 632, 633, 643, 854, 855, 865, 1029, 1032), in Hawaii (502), France (120), Germany (29, 204,402), Iraq (13), Iceland (469), the Lebanon (11), New Zealand (816), India and Ibiza (pers. observ.); it has been recorded a few times from water in Denmark (569), Germany (402), the USSR (559) and the Netherlands (743).

Several records are known from plants and roots: In Hawaii from species of Ananas, Cajanus, Canavalia, Ipomoea, Pennisetum, Saccharum, Solanum, Vicia and Zea (728, 889, 891), in the USA from species of Avena, Erica, Fuchsia, Hordeum, Lactuca, Lathyrus, Lupinus, Medicago, Nemophila, Oryza, Persea, Phaseolus, Spinacia, Triticum, Vicia (643), Medicago (108), sweet clover (339), Citrus (1067), several grasses (925, 927), various ornamentals (363), peach trees (376, 664), Cleyera, Ilex and Photinia (363); in Germany from Lupinus (862), In England from spruce (1075), in Argentina from Pinus, Lycopersicon and Trifolium (291), in Canada from Fragaria (705), in New Zealand from peat, roots and vegetable crops (816, 819), and in the Netherlands from roses and begonia (743).

When tested, P. rostratum is mostly seen to be non-pathogenic or very weakly pathogenic, e.g. to spruce (1075), clover and alfalfa (338, 339), maize (409), pineapple (502), cereals (497), peach seedlings (664), strawberry (705) and tomato seedlings (817). It is rarely found to be pathogenic, e.g. to roots of species of Ananas, Cajanus, Canavalia, Ipomoea, Pennisetum, Saccharum, Solanum, Vicia and Zea (889, 954).

Fig. 75. - P. salinum. a. mycelial habit with accumulations of resting sporangia, b1-2. oogonia, b1 with monoclinous antheridia, c. discharging sporangium (redrawn from Hhnk, 1953).

[p. 145]

68. Pythium salinum Hhnk - Fig. 75.

Pythium salinum Hhnk - Verff. Inst. Meeresforsch. Bremerh. 2: 89. 1953.

Main hyphae up to 5 m wide. Sporangia (sub)globose, smooth, (8-)16-21.5(-24.5) m diam; zoospores up to 25 in a vesicle. Oogonia (sub)globose, smooth, 8-24 m diam. Antheridia monoclinous and diclinous, 1 or more per oogonium. Oospores globose, smooth, (11-)15-17.5(-19) m diam, plerotic, wall about 1.5 m thick.

No material available.

Discussion

P. salinum was originally isolated from seawater near Kiel, Germany. It differs from P. rostratum and P. hypogynum by its lack of hypogynous antheridia. It has smaller sporangia than P. tracheiphilum. The other known species with globose sporangia and smooth oogonia have aplerotic oospores. P. pleroticum does not form sporangia and has smaller oogonia than P. salinum. The species was also mentioned by Johnson and Sparrow (1960); no other records are known.

Fig. 76. P. salpingophorum, CBS 471.50. a1-7. oogonia, some with antheridia, b1-4. sporangia with discharge tubes, c1-3. appressoria.

[p. 146]

69. Pythium salpingophorum Drechsler - Fig. 76.

Pythium salpingophorum Drechsler - J. Wash. Acad. Sci. 20: 407. 1930; Phytopathology 30: 805. 1940.

Colonies on cornmeal agar submerged, on potato-carrot agar not showing a special pattern. Main hyphae up to 7 m wide; sometimes developing elongated, often catenulate appressoria. Sporangia terminal or intercalary, occasionally proliferating, (sub)globose, (14-)17-19(-23) (av. 22.3) m diam; zoospores formed at 15C; discharge tubes often formed near a septum, 4-45 m long and 3-4 m wide; the distal part often widening trumpet-like. Encysted zoospores 10-12 m diam. Oogonia mostly intercalary, often 2-5 in chains, connected by hyphal parts or unilaterally intercalary, smooth, (11-) 15-19(-25) (av. 16.5) m diam. Antheridia 0-3 per oogonium, monoclinous and originating immediately under the oogonium, or diclinous. Oospores plerotic (10-)14-18(-24) (av. 15.5) m diam, wall 1-1.5(-3) m thick, appearing fused with the oogonial wall.

Cardinal temperatures: minimum 5C, optimum 25C, maximum 30C. Daily growth rate on cornmeal agar at 25C: 20 mm.

Description based on CBS 471.50.

Material examined

CBS 471.50 and 472.50, isolated from Lupinus angustifolius and L. luteus, respectively, Germany, H. Richter, 1942. CBS 326.62, isolated from agricultural soil, Germany, by W. Gams, comm. K. H. Domsch, 1962. CBS 165.68 = IMI 120400, isolated from soil, USA, A. F. Schmitthenner.

Discussion

The sporangia rarely proliferate; their intercalary position, often close to a hyphal tip, the location and distal widening of the discharge tubes are characteristic. Some isolates studied do not produce proliferous sporangia and were therefore initially identified as P. conidiophorum. However, all other characteristics agree well with Drechslers description: oospores often arranged like a string of beads and mostly lack antheridia; antheridia, if present, originate from the oogonial stalk adjacent to the oogonium and are rarely diclinous.

Occurrence and pathogenicity

P. salpingophorum was originally isolated from decaying roots of Pisum sativum near Eden, N.Y. USA. It is not common; only few records are known. It has been isolated from soil and diseased plants in Germany (863) and some of the isolates listed above also come from Germany; in the USA it has been isolated from Spinacia oleracea, flax, peas (416), Ceanothus cyanus and Lycopersicon esculentum (643); in Canada it has been recorded from soil (1032).

In infection experiments P. salpingophorum caused severe damping-off in Lupinus sp. and Trifolium incarnatum; it seemed to be weakly pathogenic to other tested Leguminosae (416). [p. 147]

Fig. 77. - P. scleroteichum, CBS 294.37. a1-8. various stages of oogonia and antheridia.

 

70. Pythium scleroteichum Drechsler - Fig. 77.

Pythium scleroteichum Drechsler - J. agric. Res. 49: 887. 1934.

Colonies on cornmeal agar and potato-carrot agar submerged without a special pattern. Main hyphae up to 7 m wide. Appressoria often present. Sporangia never [p. 148] observed. Oogonia smooth, globose, terminal or intercalary, (17-)21-29(-34) (av. 25.3) m diam. Antheridia 1-5 per oogonium, stalks mostly monoclinous, sometimes diclinous, branched or unbranched, often with dorsal furrows or constrictions, entangling the oogonium; antheridial cells mostly 4-7 m long. Oospores aplerotic, yellowish, (13-)16-25(-30) (av. 20) m diam, wall 0.8-1.5 m thick.

Cardinal temperatures: minimum 10C, optimum 25C, maximum 32C. Daily growth rate on cornmeal agar at 25C: 20 mm.

Description based on CBS 294.37.

Material examined

CBS 294.37, isolated from Ipomoea batatas, USA, comm. C. Drechsler, 1937.

Discussion

The oospores often degenerate in artificial cultures unless the medium has a pH of 4.5-5.0. Drechsler did not observe zoospores. In spite of several trials at various temperatures, the isolate CBS 294.37 did not form zoosporangia and zoospores. Though Drechsler included this species in Pythium, there may be objections because of the lack of zoospores and some resemblance of the oogonia to those found in Aphanomyces. P. scleroteichum differs from other Pythium species by its furrowed antheridial stalks.

Occurrence and pathogenicity

P. scleroteichum has already been isolated by Harter and Whitney (349) during their study of mottle necrosis of sweet potato, but was not described until 1934 by Drechsler, who isolated it on several occasions from various states in the USA, though always from Ipomoea. Only a few later records from Ipomoea in the USA are known (389, 609). According to Fitt and Hornby (296), P. scleroteichum does not affect transport processes or shoot growth in wheat.

 

71. Pythium spinosum Sawada - Fig. 78.

Pythium spinosum Sawada apud Sawada & Chen - Trans. nat. Hist. Soc. Formosa 16: 199. 1926 (reproduced as Rep. Gov. Res. Inst. Formosa 27: 5. 1927).

?Pythium artotrogus var. macracanthum Sideris - Mycologia 24: 47. 1932.

?Pythium betae Takahashi - Ann. phytopath. Soc. Japan 38: 309. 1972 (cf. p. 187).

Colonies on cornmeal agar arachnoid-cottony, on potato-carrot agar with a slight radiate pattern. Main hyphae 2.5-5(-7) m wide. Sporangia and zoospores not formed. Terminal and intercalary hyphal swellings present, globose or limoniform, thin-walled, mostly smooth, but occasionally with 1 or 2 digitate protuberances, up to 33 m diam. Oogonia terminal or intercalary, globose or fusiform, (14-)17-21 (av. 18.5) m diam, provided with a varying number of blunt, digitate ornamentation, 3.5-8.5 m long and 1.5-2.0 m diam at the base. Antheridia 1(-3) per oogonium, monoclinous, occasionally [p. 150] diclinous, soon vanishing after fertilization; antheridial cells hardly inflated. Oospores plerotic, occasionally aplerotic, (13-)15-19(-20) (av. 17.2) m diam, thin-walled.

Fig. 78. - P. spinosum, CBS 276.67. a1-9. oogonia and antheridia, b1-5. hyphal swellings, c1-2. appressoria, d. hyphae with spine-like projections.

Cardinal temperatures: minimum 5C, optimum 25C, maximum 35C. Daily growth rate on cornmeal agar at 25C: 30-35 mm.

Description based on CBS 275.67.

Material examined

CBS 270.31, isolated from Carica papaya, South Africa, by V. A. Wager, comm. S. F. Ashby, 1931. CBS 274.67, isolated from soil, Florida, USA, by A. F. Schmitthenner, comm. G. M. Waterhouse, 1967. CBS 275.67 and 276.67, isolated from compost and Zinnia sp., respectively, near Baarn, Netherlands, A. J. P.-N. 1967. CBS 377.72 = IMI 134459, isolated from Zingiber officinale, Japan, N. Hyde, 1968; and many other isolates from soil and diseased plants in the Netherlands and India.

Discussion

P. spinosum differs from the other Pythium species by its fmger-like ornamentation. Though infrequently a few spines can be conical, the majority is cylindrical with a blunt tip and 3-7(-8.5) m long. Some other species with normally smooth oogonia occasionally show a single finger-like protuberance, but never in larger numbers; only P. irregulare can produce a number of cylindrical protuberances, but these are irregularly arranged and usually fewer in number.

P. artotrogus var. macracanthum was considered by Yamamoto and Maeda (1961) to be synonymous with P. spinosum. According to the description, however, the oogonia, oospores and spines are larger than in P. spinosum. As no material is left, the identity of this isolate remains doubtful.

Occurrence and pathogenicity

P. spinosum was originally isolated from seedlings of Anthirrhinum majus in Taiwan. It is a cosmopolitan species. Records from numerous different plants but also from soil and water are known. P. spinosum has been recorded in Taiwan from Allium spp., Antirrhinum majus, Arctium lappa, Brassica spp., Calendula officinalis, Campanula media, Chrysanthemum coronarium, Citrullus vulgaris, Coriandrum sativum, Cucumis sativus, Daucus carota, Dianthus chinensis, Lactuca sativa, Lycopersicon esculentum, Raphanus sativus, Solanum melongena, Zinnia elegans (188, 849, 850) and Pachyrrhizus tuberosus (1125), in Japan from Astragalus sinensis, Campanula media, Capsicum annuum, Carica papaya, Chrysanthemum coronarium, Citrullus vulgaris, Coriandrum sativum, Cryptomeria japonica, Daucus carota, Dianthus chinensis, Eleocharis plantaginea, Fragaria grandiflora, Gypsophila sp., Hordeum vulgare, Ipomoea batatas, Pachyrrhizus tuberosus, Pennisetum barbinodum, Phaseolus aureus, Pisum sativum, Platycodon glaucus, Primula sinensis, Raphanus sativus, Saccharum officinarum, Spinacia oleracea, Trifolium repens, Vicia faba, Vigna sinensis (1117), Beta vulgaris, Brassica spp., Calendula offlcinalis, Callistephus sinensis, Cucumis sativus, Lactuca sativa, Lycopersicon esculentum, Papaverrhoeas Solanum melongena, Zinnia elegans (986, 1117) and Lotus sp. (980), in Queensland from Ananas comosus, Brassica oleracea, Camellia japonica, Carica papaya, Cucumis melo, Cucurbita maxima, PassifIora edulis, Persea gratissima, Pinus elliotii and Zingiber officinale (990, 991), in New Zealand from Aphelandra squamosa, [p. 151] Boronia megastigma, Ceanothus sp., Chamaecyparis spp., Cyperus haspan, Erica sp., Eucalyptus cinerea, Fuchsia hybrida, Grevillea sp., Hebe odora, Leucandrum sp., Lycopersicon esculentum, Pseudopanax sp., Sarothamnus scoparius and Thujopsis dolabrata (816), in India from Anacardium occidentale (776), Costus speciosus (995), soil (597, 778) and water (597), in South Africa from Carica papaya (1062, 1063), in the USA from Allium cepa (643, 870), Citrullus vulgaris (643), Camellia sp., Chrysanthemum sp., Cleyera sp., Fatsia sp., Ilex sp., Prunus persica, Rhododendron sp., various ornamentals (363, 568), Carya illinoensis (374), Lactuca sativa (246), soil (125, 363, 364, 365, 368) and water (883), on the Fidji Islands from various ornamentals (265), in Argentina from Allium spp., Antirrhinum majus, Arctium lappa, Brassica spp., Calendula officinalis, Callistephus sinensis, Campanula media, Carica papaya, Chrysanthemum coronarium, Citrullus vulgaris, Coriandrum sativum, Cucumis melo, Daucus carota, Gypsophila sp., Lactuca sativa, Lycopersicon esculentum, Papaver rhoeas, Piptadenia rigida, Primula sinensis, Solanum melongena, Zinnia elegans (291), in Hawaii from Ananas comosus, Cajanus cajan, Canavalia ensiformis Saccharum officinarum and Vigna sinensis (889), in England from Primula sinensis (178), in the Netherlands from Zinnia sp. and soil (743) and in Czechoslovakia from soil (143, 256).

P. spinosum has been shown to cause damping-off and root-rot of Antirrhinum majus (50), Lactuca sativa (246) and Allium cepa (870), in addition to many other plants (178, 568, 817, 850, 975, 985, 1117).

 

72. Pythium splendens Braun - Fig. 79, 1f.

Pythium splendens Braun - J. agric. Res. 30: 1061. 1925.

Pythium splendens var. hawaiianum Sideris - Mycologia 24: 38. 1932.

Colonies on cornmeal agar forming thick cottony aerial mycelium, on potato-carrot agar submerged of with some loose aerial mycelium with a vague radiate pattern. Main hyphae up to 9 m wide. Sporangia and zoospores not produced. Hyphal swellings abundant, globose, smooth, mostly terminal, rarely intercalary, 25-43(-49) m diam, often with dark, densely granulated contents, each germinating with 1-6 germ tubes. Oogonia generally formed in dual cultures of compatible isolates, or in single cultures in some apparently homothallic isolates; terminal or intercalary, globose, (24 -)27-32(-38) (av. 29.3) m diam. Antheridia diclinous, terminal, occasionally intercalary, 1-8 per oogonium; stalks sometimes branched or bifurcate, often encircling the oogonium; antheridial cells large, often 20 x 15 m, straight or crook-necked. Oospores aplerotic, (20-)22-28(-33) (av. 25) m diam, wall 1-3 m thick.

Cardinal temperatures: minimum 5C, optimum 25C, maximum 34C. Daily growth rate on potato-carrot agar at 25C: 30-35 mm.

Description based on CBS 462.48 and crossings of CBS 462.48 x CBS 266.69. [p. 152]

Fig. 79. - P. splendens. a1-9. oogonia and antheridia in CBS 462.48 x 266.69, b1-2. hyphal swellings, in b2 germinating, in CBS 462.48 and 252.28 (reproduced, with publishers permission, from Van der Plaats-Niterink, 1969).

[p. 153]

Material examined

CBS 191.25 = ATCC 1457, (-), comm. L. H. Leonian, 1925. CBS 252.28 (homothallic), isolated from roots of Nicotiana tabacum in a greenhouse in Baarn, Netherlands, A. Meurs, 1928. CBS 338.29, (-), isolated from Ananas comosus, Hawaii, C. P. Sideris (comm. as P. splendens var. hawaiianum), 1929. CBS 462.48, (-), comm. J. T. Middleton, USA, 1948. CBS 265.69 (homothallic), isolated from soil, Costa Rica, H. A. C. le Poole, 1966. CBS 266.69 and 267,69, (+), isolated from Ericaceae in a greenhouse, Ghent, Belgium, A. Roos, 1964. CBS 268.69 and 269.69,(-), comm. G. Martin, Republic Congo, 1968.

Discussion

In dual cultures of compatible isolates, P. splendens forms broad diffuse contact zones with oogonia (Fig. 1f), in contrast to narrow zones formed in P. heterothallicum, P. sylvaticum and P. intermedium (Van der Plaats-Niterink, 1969). Some isolates also form oogonia in single cultures, and oogonia can also be present in aged cultures of any isolate or in isolates kept in culture for some years. Many oospores, however, do not mature but degenerate. Attempts to trace the oogonial and antheridial origins failed, so the compatibility types of the isolates are indicated with + or -. P. splendens also differs from the above three heterothallic species in its larger hyphal swellings, oogonia and oospores and thicker oospore walls. Isolate CBS 338.29 shows a good sexual reaction with CBS 266.69 and 267.69; it differs slightly from other isolates by having larger hyphal swellings, but this is not sufficient to distinguish it as a variety.

Occurrence and pathogenicity

The overall distribution of P. splendens is shown on the CMI Map No. 433, 1979. It was originally isolated from Pelargonium cuttings in the USA and later from many ornamentals in the USA and Canada (153, 201, 363, 508, 509, 511, 596, 639, 642, 643, 813, 1088). It has also been reported in the USA from Cucumis, Raphanus (98), Phaseolus, Ipomoea (349), Medicago (108), Citrus, Hordeum (643), rhubarb, Pisum (648), maize (409), pear trees (928), Carthamus tinctorius (504, 996, 1130), Gossypium (344), soil (82, 126,153), and water from irrigation ponds (884). In Hawaii this species has been reported from Cajanus, Canavalia, Helianthus, Ipomoea, Saccharum, Triticum, Vicia, Vigna, Ananas, and Phaseolus (502, 728, 887, 889, 891). It has also been reported in many other countries, mostly from warmer regions: In S. Africa (1062,1066), in Malaysia from Begonia (880), Piper (1003), Tithonia (473), Anacardium, Celosia, Citrus, Elaeis, Hevea, Mangifera, Manihot, Persea, Pinus, Piper, Solanum, Theobroma, Vitis and Zingiber (557), in Indonesia from Corchorus (810,1007), tobacco (743) and Brassica (1053), in Australia from Pelargonium (472), Annona, Pisum, and Pinus (991) and other diseased plant material (755), in New Zealand from Nerium, Aralia, Fatsia, Eucalyptus, Polygala and Luculia (816), in Nigeria from oil palm and soil (678), in the Congo from various plants (804), in the Sarawak from pepper seedlings (25), in Cambodja, Laos and Vietnam from pear (51), in Taiwan from soil and roots (424), in Puerto Rico from Anthurium (555), in Germany from Cattleya (531), in Italy from pepper and cucumber seedlings (171) and in Ireland from various diseased plants (521).

P. splendens has been shown to be pathogenic to many plants, paticularly seedlings and cuttings: Pelargonium (98, 109), Cucumis, Raphanus, Coleus, Begonia (98), Chrysanthemum (109), Ananas (502, 891), various Leguminosae (647, 648), rhubarb (644), maize (409, 410), Medicago and sweet clover (339), Tithonia (473), Anthurium [p. 154](555, 844), pepper (25), safflower (996, 1130), Philodendron, Scindapsus (509), Cattleya (531), Caladium (813) and Brassaia (511), Aglaonema, Peperomia and Platycerium (844).

Infected soil could be a source of root-rot and stunting of Peperomia seedlings (15 3). Antagonists (Trichoderma viride, Streptomyces sp., Penicillium funiculosum) drastically reduced the infection of Pelargonium hortorum with P. splendens causing blackleg disease (82, 83).

Fig. 80. - P. sulcatum, CBS 603.73. a1-6. oogonia and antheridia, b1-2. filamentous sporangia, c. appressoria.

 

73. Pythium sulcatum Pratt & Mitchell - Fig. 80.

Pythium sulcatum Pratt & Mitchell - Can. J. Bot. 51: 334. 1973.

Colonies on cornmeal agar submerged, on potato-carrot agar with a radiate pattern. Main hyphae up to 7 m wide. Appressoria sausage-shaped, often catenulate. Hyphal [p. 155] swellings (sub)globose, elongate, obpyriform, ovate or peanut shaped, up to 45 x 26 m, sometimes formed in the oogonial stalk at varying distances below the oogonium. Sporangia filamentous, not differentiated from the vegetative hyphae. Zoospores formed at 20C. Encysted zoospores 9-13 m diam. Oogonia terminal or intercalary, (sub)globose, smooth, (14-)15-17(-21) (av. 16.5) m diam. Antheridia 1-3 per oogonium, monoclinous and diclinous; stalks often branched; antheridial cells very variable in size, often large, longitudinally appressed to and encircling the oogonium, having marked or slight folds and furrows, sometimes smaller and clavate or crook-necked. Oospores aplerotic, 13-15(-18) (av. 14.5) m diam, wall 1-1.5 m thick.

Cardinal temperatures: minimum 2-3C, optimum 20-28C, maximum 36-37C. Daily growth rate on potato-carrot agar at 25C: 13-14 mm.

Description based on CBS 603.73.

Material examined

CBS 603.73, type culture, isolated from roots of Daucus carota, Wisconsin, USA, R G. Pratt and J. E. Mitchell, 1973. CBS 604.73, isolated from soil and dung on a carrot farm, Florida, USA, R. G. Pratt and J. E. Mitchell, 1973. CBS 292.76, isolated from parsley, Ontario, Canada, D. J. S. Barr, 1973.

Discussion

Only P. scleroteichum has rather similar, complicatedly furrowed antheridia, but in P. sulcatum they are even more irregular than in P. scleroteichum. Moreover, the oogonia and oospores of P. sulcatum are considerably smaller than those of P. scleroteichum, and it has hyphal swellings, a lower growth rate and filamentous, non-inflated sporangia. Zoospores are produced at about 20 C, whilst in P. scleroteichum no sporangia are known. Other species with filamentous sporangia do not form such complicated antheridia.

Occurrence and pathogenicity

P. sulcatum was originally isolated from carrot roots in Wisconsin, USA. Further records come mostly from carrots or soil under carrots, besides one record from parsley (53, 421, 422, 480, 1110). This species was shown to be pathogenic to carrots, causing brown discolorations, root die-back and tap-root forking (53, 421, 422, 480, 487, 758).

 

74. Pythium sylvaticum Campbell & Hendrix - Fig. 81, la.

Pythium sylvaticum Campbell & Hendrix - Mycologia 59: 274. 1967.

Pythium debaryanum var. pelargonii Braun - J. agric. Res. 30: 1060. 1925.

Colonies on cornmeal agar producing cottony aerial mycelium, on potato-carrot agar submerged and showing a radiate pattern. Main hyphae up to 11 m wide. Appressoria simple or complex, clavate or sickle-shaped. Sporangia and zoospores not produced. Hyphal swellings frequent, globose or limoniform, intercalary or terminal, up to 32 m diam. Oogonia sometimes produced in single cultures, but most abundantly in dual [p. 156] cultures of compatible isolates, forming a whitish line of contact which is rather sharp to the side of the antheridial isolate and diffuse towards the oogonial side. Oogonia smooth, terminal or intercalary, (16-)18-20(-21) (av. 19.3) m diam. Antheridia 2-4 per oogonium, diclinous; antheridial stalks branched, often bifurcate near the oogonium, soon vanishing after fertilization; antheridial cells inflated. Oospores aplerotic, (13-)15-18 (-19) (av. 16.5) m diam, wall 1-2 m thick.

Fig. 81. - P. sylvaticum, CBS 234.68 x 230.68 or 231.68. a1-5. oogonia and antheridia, b1-2. hyphal swellings (reproduced, with publishers permission, from Van der Plaats-Niterink, 1968).

Cardinal temperatures: minimum below 5C, optimum about 25C, maximum between 35 and 40C. Daily growth rate on potato-carrot agar at 25C: 30 mm or more.

Description based on CBS 452.67 and dual cultures with CBS 453.67.

Material examined

CBS 452.67 (antheridial), and 453.67 (oogonial), type cultures, isolated from soil, Georgia, USA, F. F. Hendrix Jr. and W. A. Campbell, 1967. CBS 226.68 (antheridial), isolated from Crocus sp., Netherlands, G. J. Saaltink, 1965. CBS 227.68, 228.68 and 233.68 (antheridial), isolated from Pisum sp., Netherlands, J. van der Spek. CBS 229.68, isolated from soil near Rhenen, 230.68, isolated from Ipomoea sp., 231.68 and 232.68, isolated from soil, Oostelijk Flevoland, all oogonial, Netherlands, A. J. P.-N., 1966 and 1967. CBS 234.68 and 235.68 (antheridial), isolated from soil near Wageningen, Netherlands, J. H. van Emden, 1967; and many other isolates not maintained in the CBS collection. [p. 157]

Discussion

P. sylvaticum is the first known heterothallic species of Pythium (Campbell and Hendrix, 1967). Fresh isolates usually show no sexual organs in single culture, but after long maintenance oogonia can be produced in single cultures, especially around the inoculum of female isolates. Often only part of the oogonia form mature oospores in both single and paired cultures. In the crossings of the type isolates on potato-carrot agar at 20C the oogonia and oospores were smaller than indicated in the original diagnosis (11-36 and 9-30 m diam, respectively). This may be due to the medium used, the temperature, or possibly the prolonged cultivation. In crossings of four oogonial isolates with five different antheridial partners, the average size of the oogonia and oospores varied and was determined by the female isolate. The antheridial partner had no influence on the size of these organs (Van der Plaats-Niterink, 1968). The line of contact in paired cultures is characteristically formed, rather sharp to the side of the antheridial partner, but forming more or less tree-shaped ramifications towards the oogonial side (Fig. 1a). In slide cultures, the origin of oogonia and antheridia to their respective colony could be traced (Papa et al., 1967; Van der Plaats-Niterink, 1968). Sexual characteristics were also studied by Pratt and Green (1973).

The addition of sterols to the culture medium of the oogonial or of both strains increased the number of oogonia formed, but not when it was added to the antheridial strain only (Kaosiri and Hendrix, 1972; Pratt and Mitchell, 1973).

In former years, P. sylvaticum has often been erroneously identified as P. debaryanum. Braun (1925) described P. debaryanum var. pelargonii with smooth oogonia and aplerotic, but often abortive oospores of the same size as those of P. sylvaticum. From the description this variety must be considered as synonymous with P. sylvaticum (Pratt and Green, 1971; Hendrix and Campbell, 1974). However, the present writer cannot agree with Hendrix and Campbell (1974) that P. debaryanum Hesse sensu Middleton and P. debaryanum var. viticola Jain are synonymous with P. sylvaticum. P. debaryanum sensu Middleton is nearer to P. irregulare. P. debaryanum var. viticola differs from P. sylvaticum in its larger oogonia and oospores, thicker oospore walls and fewer antheridia. This taxon does not fit in a known species and was invalidly published (Art. 36).

Occurrence and pathogenicity

P. sylvaticum was originally isolated from soil in the USA. Since then several records from soil have become known: In the USA and Canada (127, 364, 368, 371, 1034), the Netherlands (740, 743), Germany (K. H. Domsch, pers. comm.) and Turkey (pers. observ.). In the Netherlands it is the commonest Pythium species. It has also been recorded from water in irrigation ponds in the USA (883) and ponds and lakes in the Netherlands (743). P. sylvaticum has also been isolated from Fragaria sp. (702) and Gossypium in the USA (466, 467), Pinus (1034) and Daucus in Canada (480), from Fragaria sp. in Japan (1081), diseased plant material in Ireland (521), Picea in Norway (296), Pyrus sp. (684), various flower bulbs and other ornamentals, pea, flax, cress, strawberry (743) and lettuce (76) in the Netherlands.

P. sylvaticum produces toxins and growth factors (76, 77); it can become pathogenic to seedlings of apple (684), wheat, flax, pea, radish, lettuce, carrot and cucumber (76, 77), strawberry (703), cotton (465, 466, 467), Pinus (1034), Picea (296) and Liquidambar (263). [p. 158]

Fig. 82. - P. tardicrescens. a1-7. oogonia and antheridia, b1-4. inflated sporangia (reproduced from Vanterpool, 1938).

 

75. Pythium tardicrescens Vanterpool - Fig. 82.

Pythium tardicrescens Vanterpool - Ann. appl. Biol. 25: 533. 1938.

Main hyphae up to 5 m wide; often forming appressoria. Filamentous, inflated, lobate or toruloid hyphal swellings present. Zoospores not observed. Oogonia globose, terminal on short side branches, occasionally intercalary, 17-30 (av. 24) m diam. Antheridia (1-)2-3(-6) per oogonium, mainly monoclinous, occasionally diclinous, terminal, clavate or crook-necked, 16 x 6-8 m, making apical contact with the oogonium. Oospores aplerotic, 16-26 (av. 20.3) m diam, wall 1.2-2.0 m thick. [p. 159]

Cardinal temperatures: minimum 7C, optimum 25C, maximum about 28C. Daily growth rate on cornmeal agar at 25C: 9 mm.

No material available.

Discussion

P. tardicrescens differs from P. aphanidermatum and P. deliense by its characteristically terminal antheridia. Intercalary antheridia are not observed in P. tardicrescens. The group of Pythium species with filamentous inflated sporangia and aplerotic oospores and smooth oogonia also comprises P. aristosporum, P. myriotylum, P. arrhenomanes, P. indigoferae, P. pyrilobum, P. helicum and P. volutum. P. myriotylum and P. arrhenomanes have more numerous and complicated antheridia, P. pyrilobum has very characteristic pyriform or irregularly inflated sporangia, P. helicum and P. volutum have antheridia which entwine the oogonial stalk, and P. indigoferae has smaller oogonia and oospores. P. tardicrescens, however, is closely related to P. aristosporum. The main differences are the somewhat larger oogonia and oospores, 1-8 or more antheridia and especially the higher cardinal temperatures of P. aristosporum. The slow growth of P. tardicrescens is obvious.

Occurrence and pathogenicity

P tardicrescens was originally isolated from diseased wheat roots in Canada and has later also been recorded in England (1042, 1043, 1044) and the USA from grasses (925). It is regarded as one of the main causal agents of browning root-rot of Gramineae (925, 1042, 1043, 1045). Its pathogenicity to sugar-cane has been demonstrated in greenhouse tests (517).

Fig. 83. - P. tenue. a1-3. oogonia and antheridia (redrawn from Gobi, 1900).

[p. 160]

76. Pythium tenue Gobi - Fig. 83.

Pythium tenue Gobi - Scripta bot. petropol. 15: 211-226. 1899 (1900) = Nematosporangium tenue (Gobi) Jasc. - Opredelitel Gribov, I. Fikomitsety, p. 96, 1931.

Pythium entophytum sensu Schenk - Ber. phys.-med. Ges. Wrzb. 9: 12-31. 1859 (non Pringsheim, 1858).

Main hyphae up to 3 m wide. Sporangia strictly flamentous, non-inflated, branched or unbranched, vesicles containing 2-16, rarely more zoospores. Oogonia globose, smooth, terminal, up to 12 (according to the illustrations, 18) m diam. Antheridia clubshaped, 1-2 per oogonium, slightly curved, monoclinous, originating from the oogonial stalk or the parent hypha, or diclinous, not cut off by a cross wall from the subtending hypha. Oospores 8-9 (according to the illustrations, -12) m diam, aplerotic, thinwalled.

No material available

Discussion

The main characteristics of P. tenue are strictly filamentous sporangia, the aplerotic thin-walled oospores and the mono- and diclinous antheridia. Gobi described the maximal sizes of the oogonia and antheridia as 12 and 9 m, respectively. In his illustrations, however, the oogonia are up to 18, the oospores up to 12 m diam.

The synonymy of P. entophyton sensu Schenk and P. tenue had already been recognized by Gobi. The morphology was discussed in papers by Middleton (1943), Matthews (1931) and Johnson (1971) who had isolates which agreed well with Gobis description. Another isolate obtained by Johnson (l.c.) ( 1969) and those of Knox and Patterson (1973) have larger oogonia and thicker oospore walls.

Occurrence and pathogenicity

P. tenue was originally isolated from diseased Vaucheria sessilis and Mesocarpus sp., both in a peat moor stream near Ny Kyrka, Finland, 1886. After the original description, it has only been recorded a few times but always from algae or water in the USA (616, 643, 918), the USSR (559, 634, 635), Iceland (469), Victorialand, Antarctica (512), and Japan (974).

P. tenue is possibly a parasite of algae and difficult to grow in culture.

 

77. Pythium torulosum Coker & Patterson - Fig. 84.

Pythium torulosum Coker & Patterson - J. Elisha Mitchell scient. Soc. 42: 247. 1927.

Colonies on cornmeal agar submerged, on potato-carrot agar exhibiting a rosette pattern. Main hyphae up to 5 m wide. Sporangia consisting of inflated branched outgrowths of the mycelium, forming toruloid complexes of various sizes. Discharge tubes long and slender; zoospores few to 25 or more formed in a vesicle at 20C, after encystment 7-8 m diam. Oogonia terminal, intercalary or terminal on short lateral [p. 162] branches, smooth, (11-)14-18(-22) (av. 15) m diam. Antheridia 1-2(-3) per ogonium, monoclinous, occasionally diclinous, borne on rarely branched antheridial stalks, originating from the oogonial stalk or the parent hypha at a distance of 1-5(-12 or more) m from the oogonium, disappearing soon after fertilization; antheridial cells allantoid clavate, 5-10 x 3-6 m, making apical contact with the oogonium. Oospores plerotic, (10-)13-17(-21) m diam, wall 1-2 m thick.

Fig. 84. P. torulosum, CBS 316.33. a1-7. oogonia and antheridia, b1-4. toruloid sporangia.

Cardinal temperatures: minimum 5C, optimum 25-30C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 15 mm.

Description based on CBS 316.33.

Material examined

CBS 316.33, isolated from diseased grass roots, Hilversum, Netherlands, A. van Luyk, 1931. CBS 405.67, 406.67 and 407.67, isolated from soil near Rhenen, near Utrecht and near Bolsward, respectively, Netherlands, A. J. P.-N., 1965 and 1966. CBS 329.62 = IMI 96347, isolated from soil under Ananas comosus, Hawaii, H. J. Klemmer, 1962.

and several isolates not rnaintained in the CBS collection.

Discussion

As no type culture of P. torulosum is available, the description is mainly based on the strain CBS 316.33 which was also studied by Vanterpool (1938) and V. and H. Kouyeas (1963). Vanterpool (1938) isolated a fungus from wheat in England which differed slightly from P. torulosum. Kouyeas (1964) described this isolate as P. vanterpoolii which can be distinguished from P. torulosum by the manner of sporangium formation: in P. torulosum lateral outgrowths from a main hypha enlarge into digitate or complex toruloid branched structures, whilst in P. vanterpoolii the sporangia are unbranched, subglobose outgrowths of the mycelium, sometimes arranged in chains. In P. torulosum the distance of the origin of the antheridial stalk to the oogonium normally does not exceed 12 m, though in water cultures it may be longer, in P. vanterpoolii this distance is mostly 25 m or more. P. dissimile, which is also very close to P. torulosum and P. vanterpoolii, is distinct in that it lacks antheridia.

Occurrence and pathogenicity

P. torulosum was originally isolated from Teleranea nematodes and Thuidium delicatulum in the USA. Coker and Patterson (174) also found it on other liverworts, mosses and water (616). In the USA and Canada P. torulosum has been recorded from barley (419) and grasses (643), including Agrostis and Festuca (419, 691), but also from Medicago (856), maize (792) and soil (126, 368, 371, 372); it has also been isolated in

The Netherlands from grasses (570) and conifers (417), in Australia from Medicago (991), in New Zealand from seedlings of various vegetable crops and soil (816, 817, 819), in Argentina from Piptadenia sp. (291), in Japan from Fragaria sp. (1079), in the USSR from water (635), and in several countries from soil: Hawaii (502), England (29, 30), Germany (401, 811), Greece (520), Iceland (468, 469), Lebanon (11), Czechoslovakia and Ibiza (pers. observ.). P. torulosum was one of the first Pythium species to appear in the newly reclaimed Zuidelijk Flevoland polder (743).

In inoculation experiments, P. torulosum was not found to be pathogenic to bean, pea, cabbage and lettuce (174), or to Lolium, Agrostis and Festuca spp. (570). It possibly causes damping-off in Pinus nigra seedlings (417) and it is pathogenic to barley, oats, wheat (497) and pineapple (502). [p. 163]

Fig. 85. - P. tracheiphilum, CBS 323.65. a1-12. young, a13-16. mature oogonia and antheridia, b1-6. sporangia, c1-3. chlamydospores (reproduced,with publishers permission, from Blok & Van der Plaats-Niterink, 1978).

[p. 164]

78. Pythium tracheiphilum Matta - Fig. 85, 8b.

Pythium tracheiphilum Matta - Phytopath. Medit. 4: 51. 1965.

Colonies on cornmeal and potato-carrot agars submerged and without a special pattern. Main hyphae up to 6 m wide. Appressoria cylindrical, club- or sausage-shaped. Sporangia terminal and intercalary, globose, 22-28(-34) (av. 24) m diam, or subglobose to elongate and 20-45 x 19-29 m. Discharge tubes up to 15 x 6 m. Zoospores formed at 16C. Encysted zoospores 8-10 m diam. Chlamydospores present in the host tissue and especially in old cultures, terminal and intercalary, smooth, variable in size and shape, thick-walled. Oogonia smooth, globose, terminal and intercalary, (13-)14-17(-18) (av. 15.5) m diam. Antheridia 1-2 per oogonium, monoclinous, originating at various distances below the oogonium, sometimes diclinous. Oospores globose, plerotic, smooth, (12-)13-16(-17) m diam, wall 1.5-3 m thick.

Cardinal temperatures: minimum below 4C, optimum 25C, maximum 27C. Daily growth rate on potato-carrot agar at 25C: 24 mm.

Description based on CBS 323.65.

Material examined

CBS 323.65, type culture, isolated from Lactuca sativa, Italy, A. Matta, 1965. CBS 870.72, isolated from Lactuca sativa, Wageningen, Netherlands, G. H. Boerema, 1972. CBS 519.77 and 520.77, isolated from Lactuca sativa, near Breda, Netherlands, J. W. Veenbaas-Rijks, 1977.

Discussion

P. tracheiphilum differs from the species with non-proliferating sporangia and smooth plerotic oospores, P. salinum and P. pleroticum, in possessing thick oospore walls. It has no hypogynous antheridia like P. rostratum and P. hypogynum, and antheridia are always present in contrast with P. salpingophorum. It has smaller oogonia and oospores than P. hemmianum. Moreover, chlamydospores shown by P. tracheiphilum have never been seen in the other species mentioned.

Occurrence and pathogenicity

P. tracheiphilum has been recorded only from lettuce, originally in Italy (612, 613), then in the Netherlands (78, 743), Germany (536, 1131) and the USA (1019). In pathogenicity tests (78) it was shown to be highly pathogenic to lettuce, cucumber and cauliflower seedlings, and somewhat less to those of tomato and pea.

 

79a. Pythium ultimum Trow var. ultimum - Fig. 86.

Pythium ultimum Trow - Ann. Bot 15: 300. 1901; var. ultimum automatically established by the distinction of var. sporangiiferum Drechsler (1960).

Pythium debaryanum sensu de Bary - Abh. senckenb. naturf. Ges. 12: 235. 1881 (non Hesse 1874).

Pythium haplomitrii Lilienfeld - Bull. int. Acad. polon. Sci. Lett. 1911: 336 (as haplomitri). [p. 165]

Fig. 86. - P. ultimum var. ultimum, CBS 398.51. a1-14. developmental stages of oogonia and antheridia, a7-14. mature oogonia and antheridia, in a3 and a8 hypogynous antheridia, b1-3. hyphal swellings.

[p. 166]

Colonies on cornmeal agar forming cottony aerial mycelium, on potato-carrot agar with a radiate pattern. Main hyphae up to 11 m wide. Sporangia mostly not formed and zoospores very rarely produced through short discharge tubes at 5C. Hyphal swellings globose, intercalary, sometimes terminal, 20-25(-29) m diam. Oogonia terminal, sometimes intercalary, globose, smooth-walled, (14-)20-24(-25) (av. 21.5) m diam; antheridia either 1(-3) per oogonium, sac-like, mostly monoclinous originating from immediately below the oogonium, sometimes hypogynous, or 2-3 and then either monoclinous or diclinous and frequently straight. Oospores single, aplerotic, globose, (12-)17-20(-21) (av. 18) m diam, wall often 2 m or more thick.

Cardinal temperatures: minimum 5C, optimum 25-30C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 30 mm.

Description based on CBS 398.51, which is designated as neotype culture.

Material examined

CBS 398.51, neotype culture, isolated from Lepidium sativum, Netherlands, G. van den Ende. CBS 114.19, isolated from coniferous seedling, comm. C. Hartley, 1919. CBS 249.28, isolated from Sinningia sp., Netherlands, A. Meurs, 1928. CBS 291.31 = ATCC 11123. isolated from Dioscorea batatas, comm. F. Labrousse, 1931. CBS 378.34, isolated from Trifolium pratense, Netherlands, A. Meurs, 1934. CBS 305.35, isolated from grass roots, Netherlands, A. van Luijk, 1935. CBS 296.37, isolated from Pisum sativum, England, comm. L. Ogilvie, 1937. CBS 264.38, isolated from Pinus sylvestris seedling, Netherlands, J. G. ten Houten. CBS 656.68, isolated from Lycopersicon esculentum, Netherlands, G. Weststeijn and many other isolates not maintained in the CBS collection.

Discussion

Trow (1901) considered P. ultimum to be non-parasitic in contrast to P. debaryanum. Drechsler (1927) stated that P. ultimum has often been misidentified as P. debaryanum. Van Luijk (1934) regarded Hesses pictures of P. debaryanum as rather doubtful, but did not reject the name, and regarded the fungus described by De Bary (1881) as P. debaryanum; he thus preferred to use the name P. debaryanum Hesse emend. de Bary to P. ultimum. Indeed De Barys description closely agrees with Trows diagnosis of P. ultimum but not with Hesses description of P. debaryanum. One difference between De Barys and Trows descriptions may be noted: De Bary described and illustrated hypogynous antheridia which were not mentioned by Trow. However, the present author found this kind of antheridium only rarely in some isolates, frequently or of intermediate abundance in others. The description of P. haplomitrii closely fits that of P. ultimum and leaves no doubt about the synonymy.

P. ultimum can be distinguished from its congeneric species by the combination of sac-like monoclinous antheridia, a thick oospore wall and globose hyphal swellings or sporangia.

Occurrence and pathogenicity

P. ultimum var. ultimum was originally isolated from rotten cress seedlings in England; it is cosmopolitan and occurs in cool to moderately warm climates. Its overall distribution is shown on CMI Map No. 207. 1965. P. ultimum is one of the commonest Pythium species in the soil (345, 469, 525, 567, 658, 743, 864, 865, 942, 1032, 1039). It has frequenty been recorded from California (345, 639, 640, 642, 643, 644, 649, 1014, 1017, 1018), Texas (904), Hawaii and Tahiti (864, 954) and other states of the [p. 167] USA (37, 226, 486, 545, 568, 582, 642, 650, 658, 736, 737, 852, 924,1004), Canada (389,1037), South America (20), Iceland (469), S. Africa (1062, 1066, 1067), Nigeria (262), Kenya (pers. observ.), Congo (804), Egypt (241), Japan (16), Australia (489, 1030, 1039), Germany (204, 859), Britain (521, 683), Denmark (683), Greece (520), Turkey (pers. observ.), Czechoslovakia (145, 147, pers observ.), France (275) and the Netherlands (204, 571, 743, 831).

Root exudates of different seedlings stimulate the growth of hyphae and the germination of hyphal swellings. Especially sugars and amino acids are responsible for this effect (7, 316, 486 524, 614, 885, 902, 944, 1035); on the other hand, some sterols (-sitosterol) inhibit pectinase activity but stimulate oogonium production (630, 631). So far unidentified growth-inhibiting factors have been found in soil extracts (1033, 1035), with molecular weights varying from 3000-55000, and one of about 150 Dalton.

Hyphal swellings of P. ultimum can persist for 11 months in air-dried or moist soil (943); after 2 years storage at -18C, Pythium-infested soil was still infective to aster and pea seedlings (688). Generally temperatures below 20C, moist conditions and organic amendments (sugars, amino acids) enhanced growth and germination of P. ultimum in the soil (689).

P. ultimum can become a severe parasite on many plants, it is a causal agent of damping-off and foot rots. Lehman and Wolf (545), like many students of plant diseases, identified a soya bean parasite as P. debaryanum but clearly described P. ultimum. As P. ultimum can become pathogenic to most of the plants from which it has been isolated, no distinction is made between data on origin and pathogenicity tests. Many investigators mentioned P. ultimum, P. debaryanum or both as the cause of damping-off, stunting or bald-head of soya beans (100, 101, 102, 168, 388, 389, 486, 543, 752, 924, 959, 997, 1004); also Phaseolus and Pisum spp. can be attacked by P. ultimum (252, 390, 490, 525, 525, 614, 647, 648, 649, 689, 885, 944) as well as Colchicum (682), tulips (331, 681, 682, 683), crocus(1013), hyacinth (831), Cattleya (36), Antirrhinum (630, 631), begonia (639, 642, 650), Parthenium (128, 129), Poinsettia (955, 1018), Plantago (154), various Gramineae (571, 680), sweet potato (750, 1062), Zantedeschia (1014), sugar beet (316, 1098), Pinus sylvestris (859), a variety of other tree-seedlings (1040, 1041), coffee (262), apple (69), pumpkin and watermelon (1016), rhubarb (644,1062), Chrysanthemum (568), cotton (37), peach (657), sugar cane (954), dahlia (147) and Citrus (586, 1062).

 

79b. Pythium ultimum var. sporangiiferum Drechsler - Fig. 87.

Pythium ultimum var. sporangiiferum Drechsler - Sydowia 14: 107. 1960 (as sporangiferum).

Sporangia and zoospores readily formed; sporangia (sub)globose, intercalary and terminal, (23-)27-32 (av. 28.5) m diam, with one, sometimes 2 discharge tubes, (5-)23-38(-156) x 3-11 m, often slightly wider near the base; zoospores easily released at 20 C; formation of germ tubes is also observed. Oogonia globose, smooth, usually terminal though sometimes intercalary, (15-)19-24(-26) (av. 22.3) m diam; antheridia and oogonia as in var. ultimum. [p. 168]

Fig. 87. - P. ultimum var. sporangiiferum, CBS 219.65. a1-6. oogonia and antheridia, b1-7. emptied sporangia with discharge tubes.

Cardinal temperatures: minimum 5C, optimum 25-30C, maximum 37-40C. Daily growth rate on potato-carrot agar at 25C: 30 mm.

Description based on CBS 219.65.

Material examined

CBS 219.65 = ATCC 13647, type culture, isolated from Chenopodium album, Maryland, USA, C. Drechsler. CBS 111.65, isolated from alfalfa, Beirut, Lebanon, H. C. Weltzien. CBS 171.68 = IMI 120411, isolated from alfalfa, England, comm. G. M. Waterhouse. CBS 114.79, isolated from soil, Ibiza, A. J. P.-N., 1973. [p. 169]

Discussion

P. ultimum var. sporangiiferum mainly differs from var. ultimum by its capicity to release zoospores at room temperature. In var. ultimum zoospores are only formed under special conditions (Drechsler, 1946a): oospores of 3-month-old cultures placed in water produced zoospores.

Occurrence

P. ultimum var. sporangiiferum has been recorded only a few times. Kouyeas (1964) observed zoospore-producing isolates of P. ultimum in England and Greece, but did not consider the differences sufficient to retain two varieties in P. ultimum. Ark and Middleton (1949) isolated a sporangium- and zoospore-producing strain of P. ultimum from Cattleya in the USA which may have been identical to var. sporangiiferum.

 

80. Pythium uncinulatum Van der Plaats-Niterink & Blok - Fig. 88, 6d, 7f.

Pythium uncinulatum Van der Plaats-Niterink & Blok - Neth. J. Pl. Path. 84: 135. 1978.

Colonies on cornmeal and potato-carrot agars submerged and without a special pattern. Main hyphae up to 7 m wide. Appressoria large, sausage- or club-shaped, catenulate. Sporangia globose, mostly produced within the host plant (lettuce), terminal, occasionally intercalary, (20-)30-40 (av. 34.5) m diam. Discharge tubes up to 200 m long. Zoospores produced at 13-15C. Encysted zoospores 15-16 m diam. Oogonia terminal, (24-)31-38(-39) (av. 34) m diam, ornamented; projections conical, acute, 7-10 m long and 4-5 m diam at the base, slightly bent and resembling rose thorns, sometimes with two tips, about 30 visible in optical section; oogonial stalks bent, 6 m wide, sometimes widening near the oogonium. Antheridia diclinous, one stalk per oogonium, bearing 1-8 antheridial cells, cells mostly broadly applied to the oogonium near its stalk. Oospores globose, aplerotic, (21-)27-35 (av. 30.5) m diam, wall 3-4 m thick.

Cardinal temperatures: minimum 5C, optimum 24-25C, maximum 30C. Daily growth rate on potato-carrot agar at 25C: 15 mm.

Description based on CBS 518.77.

Material examined

CBS 518.77, type culture, isolated from Lactuca sativa near De Meern, CBS 515.77, isolated from Lactuca sativa near Breda, CBS 516.77 and 517.77, isolated from Lactuca sativa, Wageningen, Netherlands, J. W. Veenbaas-Rijks, 1975-77.

Discussion

Sporangia were produced in water cultures inside sterilized lettuce seedlings. The discharge tubes grew through to the surface of the tissue and their length depended on the locations of the sporangium in the tissue. The antheridia form a complicated knot consisting of swollen branches and diverticles around the oogonium, mostly near the often [p. 171] curved oogonial stalk. The ornamentation differs from that of all other spiny Pythium species. P. uncinulatum is nearest to P. mastophorum, but differs from it in its often curved oogonial stalks and the shape of the ornamentations. It differs from P. polymastum in its smaller oogonia and oospores, more regular sporangia, curved oogonial stalks and shape of the ornamentations.

Fig. 88. - P. uncinulatum, CBS 518.77. a1-8. stages in development of oogonia and antheridia, b1-2. young and emptied sporangia, c. encysted zoospores, d. inflated hypha (reproduced, with publishers permission, from Blok & Van der Plaats-Niterink, 1978).

Occurrence and pathogenicity

P. uncinulatum was originally isolated from diseased lettuce in the Netherlands. It is highly pathogenic to seedlings of lettuce, and somewhat less so to those of cucumber and tomato (78).

Fig. 89. - P. undulatum, CBS 157.69. a1-12. sporangia, some with proliferations, b1-4. chlamydospores.

[p. 172]

81. Pythium undulatum H. E. Petersen - Fig. 89, 4b.

Pythium undulatum H. E. Petersen - Bot. Tidsskr. 29:394. 1909; Annls mycol. 8:531. 1910 = Pythiomorpha undulata (H. E. Petersen) Apinis - Acta Horti bot. Univ. Latv. 4: 234. 1929.

Pythium undulatum var. litorale Hhnk - Verff. Inst. Meeresforsch. Bremerh. 2: 81. 1953.

Colonies on cornmeal agar submerged, on potato-carrot agar showing a radiate pattern. Main hyphae up to 7 m wide. Sporangia proliferating internally by 1 or more sporangiophores, sometimes provided with a hyaline papilla, often very long, (27-) 45-118(-156) x (12-)20-44(-50) m (av. 77.5 x 33 m), mostly forming short discharge tubes. Zoospores produced at 5-20C. Chlamydospores present, dark yellow, thick-walled (2-5 m), (sub)globose, intercalary and terminal, (16-)21-61(-75) (av. 36) m diam. Oogonia, antheridia and oospores not observed.

Cardinal temperatures: minimum 5C, optimum 20-25C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 20 mm.

Description based on CBS 157.69, which is designated as neotype culture.

Material examined

CBS 323.47, isolated by E. K. Goldie-Smith, comm. E. M. Blackwell, 1947. CBS 157.69, neotype culture isolated from soil under Pinus sp., Alabama, USA, W. A. Campbell, 1969. CBS 346.69, isolated by M. W. Dick, Canada. CBS 113.79 = IMI 35558, isolated from plant debris in water, Roughton, England, G. M. Waterhouse, 1949.

Discussion

P. undulatum differs from the other species with proliferating sporangia in the extraordinary dimensions of the sporangia (up to over 150 m long). Sexual organs have not yet been observed and could not be obtained by cross matching of the four isolates studied. In all four isolates dark yellow chlamydospores were observed though in varying amounts and sizes; in CBS 157.69 they were particularly large and often attained 75 m diam. Petersen did not describe them, but Dissmann (1927), Matthews (1931), Sparrow (1932, 1959), Drechsler (1946a), Van Beverwijk (1948) and Goldie-Smith (1952) all recorded chlamydospores, sometimes referring to them as being rough. Drechsler (1946) compared them with the oospores of P. helicoides and considered them parthenospores on account of the similarity of their wall structure, their requirement of a dormancy period and production of zoospores. Dissmann (1927) already described the double layers of the chlamydospore wall; the inner layer thickens during maturation. In cultures older than 4 weeks, the outer layer of some chlamydospores ruptures and just remains as fragments on the surface. According to Dissmann (1927), the size of the chlamydospores depends on the medium, being larger in rich than in less concentrated media. In addition, the ratio between the number of sporangia and the number of chlamydospores depended on the medium used. Young chlamydospores in which the wall thickening had not yet taken place, germinated by the formation of a vesicle and zoospores; older chlamydospores only formed one or more germ tubes. When they were older than one month, they showed a thick wall and an accumulation of fat, and did not germinate (Dissmann, 1927). Drechsler (1946b) compared this phenomenon with the dormant stage of certain oospores. Dissmann (1927) and Goldie-Smith (1952) also found the size of the sporangia to vary with the medium. The proliferating hypha often branches within the sporangium and thus more than one sporangiophore emerges from the bottom of an [p. 173] empty sporangium. In rare cases subsporangial branching takes place or a new sporangium is formed immediately below the septum of the primary one. The isolates studied were very similar, CBS 113.79 differed from the others in the production of some aerial mycelium and faster growth.

Apinis (1929) changed P. undulatum to Pythiomorpha undulata because of the fact that zoospores were sometimes formed within the sporangium. Dissmann (1927) also reported a sporangium of P. undulatum containing zoospores. He regarded this as an abnormality resulting from the external conditions because of the very slow movement of the zoospores. Apinis (1929) also observed abnormal encystment and germination of zoospores. The present writer occasionally observed the formation of zoospores within a sporangium in Pythium spp. which normally produce a vesicle, e.g. in P. tracheiphilum and P. uncinulatum. Sparrow (1960) previously stated that there was no reason to change P. undulatum to Pythiomorpha. Blackwell et al. (1941) found that Pythiomorpha H.E. Petersen is a superfluous name, being a synonym of Phytophthora.

P. undulatum var. litorale was described by Hhnk (1953) as having very long (up to 423 m), sometimes constricted sporangia, which ocasionally form groups, especially in older cultures; Sparrow (1960) considered them to be malformations caused by the saline habitat. The differences between this variety and Petersens description do not warrant a separation.

Occurrence and pathogenicity

P. undulatum was originally isolated from leaves of Nymphaea alba and Nuphar luteum in Denmark. Petersen (l.c.) also mentioned isolates from fruits of Iris and tree branches. It has also been recorded mostly from water or aquatic plants in Denmark (569, 732, 733), Czechoslovakia (200), the USA (221), England (321), Germany (401, 402), the Netherlands (67), the USSR (231), Poland (1129) and India (494). A few records from soil are also known in the USA (321, 616, 864) and Iceland (469).

Little is known about the pathogenicity of P. undulatum. It could be responsible for a discoloration of Nymphaea leaves (200, 201)

 

82. Pythium vanterpoolii V. Kouyeas & H. Kouyeas - Fig. 90.

Pythium vanterpoolii V. Kouyeas & H. Kouyeas - Annls Inst. phytopath. Benaki, N.S., 5: 210. 1963.

Colonies on cornmeal agar tending to form some aerial mycelium, on potato-carrot agar showing a radiate pattern. Main hyphae up to 5 m wide. Sporangia consisting of often catenulate complexes of subglobose or irregularly ellipsoidal unbranched outgrowths of the mycelium, terminal or intercalary. Zoospores produced at 20C. Encysted zoospores 7.5 m diam. Oogonia smooth, globose, thin-walled, terminal or intercalary (11-)18-21(-22) (av. 19) m diam. Antheridia 1(-2) per oogonium, club-shaped, mostly monoclinous, occasionally diclinous; antheridial stalks originating (2-)15-25 m below the oogonium, soon disappearing after fertilization; antheridial cells 5-12 x 4-7 m. Oospores plerotic, (10-)17-20(-21) m diam, wall 2-4 m thick. [p. 174]

Fig. 90. - P. vanterpoolii, CBS 295.37. a1-8. oogonia and antheridia, b1-4. toruloid sporangia.

Cardinal temperatures: minimum 5C, optimum 25C, maximum 30C. Daily growth rate on cornmeal agar at 25C: 20 mm.

Description based on CBS 295.37.

Material examined

CBS 295.37, type culture, isolated from roots of Triticum sativum, England, T. C. Vanterpool, 1936. CBS 293.76, isolated from roots of Triticum sativum, Ottawa, Canada, D. J. S. Barr, 1974.

Discussion

Vanterpool (1938) described a Pythium species which generally agreed with the description of P. torulosum and, having no type isolate of that species available, he compared it with CBS 316.33. Vanterpools isolate differed in its tendency to form more [p. 175] aerial mycelium and in lacking the rosette growth type on certain media; moreover, the antheridia arose further away from the oogonium than in Van Luyks isolate and the oogonia were larger. Vanterpool preliminarily considered his isolate as a geographic variant of P. torulosum. Later V. and H. Kouyeas compared a number of Greek and English isolates with CBS 295.37 and CBS 316.33 of P. torulosum. They observed that besides the above differences, the sporangia of Vanterpools isolate showed asymmetrical, usually catenulate, bulbous, subglobose or irregularly ellipsoidal elements in contrast with the branched toruloid sporangial outgrowths of P. torulosum and named it P. vanterpoolii. The Italian isolate described by Petri (1930) as P. torulosum may also be identical with P. vanterpoolii.

Occurrence and pathogenicity

A few records of P. vanterpoolii are now known: In Germany it has been isolated from Sinapis, Secale and Triticum (529, 530) and in the USA from Agrostis (691) and in Malaysia from maize (557). It is supposed to be pathogenic to grasses, but not or only weakly to Triticum (528).

 

83. Pythium vexans de Bary - Fig. 91.

Pythium vexans de Bary - J. Bot Paris 14: 105-106. 1896.

Pythium complectens Braun - J. agric. Res. 29: 415. 1924.

Pythium allantocladon Sideris - Mycologia 24: 27-29. 1931.

Pythium ascophallon Sideris - Mycologia 24: 29-31. 1931.

Pythium euthyhyphon Sideris - Mycologia 24: 34. 1931.

Pythium polycladon Sideris - Mycologia 24: 32-33. 1931.

Pythium piperinum Dastur - Proc. Indian Acad. Sci. 1: 803. 1935.

Colonies on cornmeal agar with cottony aerial mycelium, on potato-carrot agar without a special pattern. Main hyphae up to 5 m wide. Sporangia sub(globose), ovoid or pyriform, occasionally proliferating, intercalary or terminal, (15-)18-23(-27) (av. 20.2) m long and (11-)15-21(-23) (av. 17.9) m broad. Oogonia mostly terminal on short side branches, sometimes lateral or intercalary, globose, (16-)18-23(-24) (av. 20.0) m diam. Antheridia 1, rarely 2, monoclinous, rarely diclinous, arising at some distance below the oogonium or from the main hyphae. Antheridial cells large, typically bell-shaped. Oospores aplerotic, (14-)16-19(-20) (av. 17.3) m diam, wall up to 1.5 m thick.

Cardinal temperatures: minimum 5C, optimum 30C, maximum 35C. Daily growth rate on potato-carrot agar at 25C: 18 mm.

Description based on CBS 119.80.

Material examined

CBS 339.29, type culture of P. ascophallon, isolated from Spinacia oleracea, Hawaii, C. P. Sideris, 1931. CBS 334.36, type culture of P. piperinum, isolated from Piper betle, India, J. F. Dastur, 1935. CBS 270.38, isolated from Medicago sativa, Iowa, USA, C. H. Meredith, 1938. CBS 455.62, isolated from Hydrangea sp., Boskoop, Netherlands, C. Dorsman, 1961. CBS 119.80, isolated from soil, Iran, D. Ershad, 1975; and many other isolates from soil and plants, not maintained in the CBS collection. [p. 176]

Fig. 91. - P. vexans, CBS 119.80. a1-5. oogonia and antheridia, b1-5. sporangia with papilla and discharge tubes.- c, d. from de Barys slide 299 in BM: c1-5. oogonia with antheridia, d1-9. sporangia or hyphal swellings.

[p. 177]

Discussion

The monoclinous bell-shaped antheridia easily distinguish P. vexans from other species with spherical sporangia and aplerotic oospores. P. complectens and P. vexans are considered synonymous as they have bell-shaped antheridia and aplerotic oospores, with equally large oogonia, oospores and spherical sporangia (Drechsler, 1946b). Sideris (1931b) described a number of species, of which P. allantocladon and P. ascophallon are identical to P. vexans. Middleton (1943) correctly placed these species in synonymy with P. vexans. And P. polycladon have asexual reproductive structures like those of P. vexans, but only produce oogonia in tissues of the host. Even though the antheridia have not been found, these isolates need not be distinguished as separate species (Middleton, 1943; Waterhouse, 1967). The description and figures of P. piperinum show sporangia which strongly resemble those of P. vexans, but the antheridia are not clearly depicted. The isolate CBS 334.36 was received from Dastur under the name P. piperinum and is thus a possible type or lectotype strain. The bell-shaped antheridia and similar oogonia, oospores and sporangia of CBS 334.36 allow the conclusion that P. piperinum is synonymous with P. vexans.

Occurrence and pathogenicity

P. vexans has been recorded from both soil and plants in several countries. Its overall distribution is shown on the CMI Map No. 205. 1980. It has been reported in Germany from Solanum tuberosum (59, 61), Lupinus sp. and Medicago sp. (862) and soil (811), in the USA and Canada from Citrus (355, 643), Hevea (156), Metrosideros (503), Persea (354, 355, 356, 643), Saccharum officinarum (784, 789, 954), grasses (372, 927), conifers (124, 969), ornamentals (71, 72, 97, 363, 639, 643), pear trees (928), peach (72, 561, 663, 664), pecan trees (374, 375) and soil (126, 368, 371, 561, 564, 633, 643, 706, 754, 864, 865, 1032), in Hawaii from Ananas (502, 887, 889), ornamentals, Spinacia, Ricinus, Carica (887, 889) and soil (64), in India from Zingiber, Eletteria, Cinchona, apple grafts, Pelargonium and Piper spp. (122, 727, 775, 794), potato (185) and Aframomum sp. (1107), in Malaysia from Theobroma, Hevea, Thea, Camellia, Dianthus, Carica, Citrus, Piper, Saccharum, Vicia, Vigna, Vitis, Zingiber and a number of ornamentals (473, 557, 880, 999, 1000, 1002, 1003), in England from cereals (837), in Java from Nicotiana (770), in Rumania from tomato and potato (847). In Uganda from Pelargonium (346), in South Africa from Citrus, pawpaw and avocado (1063, 1066, 1067), in Indo-China from Hevea and Pyrus (24, 51, 822), in Australia from tomato seedlings (489), pawpaw, Annona, Brassica and Persea (990, 991), in Argentina from ornamentals and Citrullus vulgaris (291), in the Congo from various cultivated plants (804), in Brazil from Strelitzia sp. (141), in Papua-New Guinea from Cocos and Theobroma (935), in Pakistan from Dianthus (45), in the Netherlands from Linum (199) and Hydrangea (743). P. vexans was also isolated from soil in Iceland (469), Czechoslovakia (146), France and England (120), Lebanon (11), Iraq (13), Madeira (403) and Japan (49, 974).

Many tests have been done to ascertain the pathogenicity of P. vexans. It is considered to be pathogenic to Pelargonium (97, 775), Zingibe r(727, 775), cardamon (775,1107), holly (72), carnation (45, 767), pecan seedlings (374), potato and sweet potato (975), Metrosideros (503), some Proteaceae (767), Aframomum (1107), Cinchona (775), pears (51) and Nicotiana (770). P. vexans has been regarded as the causal agent of patch canker in Hevea (823, 858, 880), though inoculation experiments do not always give the [p. 178] symptoms of the disease (156). P. vexans has often been isolated with Phytophthora cinnamomi from declining peach trees in which case it is normally of secondary importance (663, 664, 665), though Hendrix and Campbell (364) do give cases of true pathogenicity. P. vexans shows no or only weak parasitism on Pinus spp. (124, 364), avocado (355, 356), pawpaw (1067), tomato, watermelon, morning-glory seedlings, squash, kidney bean, rice (975), pineapple (889) and cereals (837, 1072).

Fig. 92. - P. violae, CBS 159.64. a1-2. oogonia and antheridia.- a3-93 various stages in development of oogonia and antheridia (reproduced, with publishers permission, from Chesters and Hickman, 1944).

 

84. Pythium violae Chesters & Hickman - Fig. 92, 2d.

Pythium violae Chesters & Hickman - Trans. Br. mycol. Soc. 27: 60. 1944.

Colonies on cornmeal agar with some aerial mycelium, on potato-carrot agar showing a radiate pattern (Fig. 2d). Main hyphae up to 6 m wide. Sporangia unknown. Hyphal [p. 179] swellings present, terminal and intercalary, (16-)25-30(-32) (av. 27.5) m diam. Oogonia globose, terminal or intercalary, smooth, (25-)27-38 (av. 29.5) m diam. Antheridia 1-8 per oogonium, mostly monoclinous and sessile but also stalked, or diclinous, terminal or sessile. Oospores aplerotic, (22-)24-30(-32) (av. 27) m diam, Wall up to 3 m thick.

Cardinal temperatures: minimum 5C, optimum 25C, maximum below 35C. Daily growth rate on potato-carrot agar at 25C: 15 mm.

Description based on CBS 159.64.

Material examined

CBS 159.64, isolated from soil, Australia, O. Vaartaja, 1962.

Discussion

P. violae is close to P. ultimum but differs from it in having larger oogonia and oospores, more numerous, sometimes stalked, monoclinous antheridia originating at a short distance from the oogonium and a slower daily growth rate. P. violae has larger oogonia and oospores than P. paroecandrum and P. irregulare, and a thicker oospore wall and slower growth than these two species.

Occurrence and pathogenicity

P. violae was originally isolated from Viola sp. in England. It has also been recorded in the USA from Viola sp. (223, 230) in the Netherlands from Hyacinthus and Scilla (743, 831) and in Australia from pine nurseries (1030). In all cases it was shown to be pathogenic to these plants.

Fig. 93. - P. volutum. a1-4. oogonia and antheridia, in a1-4 oogonial hypha enlacing the oogonial stalk (redrawn from Vanterpool and Truscott, 1932).

[p. 180]

85. Pythium volutum Vanterpool & Truscott - Fig. 93.

Pythium volutum Vanterpool & Truscott - Can. J. Res. 6: 77. 1932.

?Pythium helicum T. Ito - J. Jap. Bot. 20: 55. 1944.

?Pythium zingiberis Takahashi - Ann. phytopath. Soc. Japan 18: 115. 1954 (as zingiberum).

Main hyphae up to 5.5 m wide. Sporangia filamentous, inflated, with small lobes and toruloid outgrowths; discharge tubes about 50 x 3-4 m. Encysted zoospores 10-14 m diam. Oogonia smooth, (sub)globose, terminal on short side branches, occasionally intercalary, on average 30 m diam. Antheridia 3-6(-10) per oogonium, usually diclinous, sometimes monoclinous, the stalks entwining the oogonial stalk, especially in water cultures, bearing 1-4 antheridial cells which are clavate, crook-necked, curved or straight, making apical contact with the oogonium. Oospores aplerotic, smooth, globose to elongate, on average 27.5 m diam, wall up to 2 m thick.

Cardinal temperatures: minimum 4C, optimum 25C, maximum 31C. Daily growth rate on cornmeal agar at 25C: 10 m.

No material available.

Discussion

P volutum is characterized by its diclinous long antheridial stalks which coil around the oogonial stalk and the oogonium. Among the species with filamentous inflated sporangia, only two other described species, P. helicum and P. zingiberis, show similar characters. These species have about equally large oogonia and oospores. They may differ in that P. helicum has mainly monoclinous antheridia and P. volutum and P. zingiberis have mainly diclinous antheridia. The description of P. zingiberis is somewhat confusing and does not agree with the figures. P. helicum and P. zingiberis are possibly synonymous with P. volutum.

Occurrence and pathogenicity

P volutum has been recorded in Canada from wheat and oat (1048), in the USA from turf grasses (419), in the Netherlands from grasses (570, 572), in England from wheat (1042) and in Japan (as P. zingiberis) from ginger (973, 974, 975).

P. volutum is regarded as a pathogen of wheat and oats (1042, 1048), barley, rye and maize (74, 1048), various grasses (570, 572, 927), tomato, water melon, Hibiscus and morning-glory seedlings (as P. zingiberis) (974, 975, 979). [p. 181]

Appendix

Pythium fluminum Park and P. uladhum Park

These two species were isolated by Park (1974, 1975, 1976, 1977, 1980) using a technique devised to select cellulolytic fungi from streaming water. Morphologically they belong in Pythium, but in their physiological behaviour they differ from the remaining species. They are strongly cellulolytic, do not grow on media containing starch or maltose, have a great sensitivity to pentachloronitrobenzene and produce at least two pigments. The cellulolytic activity found in a number of other Pythium species is mostly confined to modified forms of cellulose: while scoured cotton is only slightly degraded, alkali-swollen cotton is strongly attacked (Taylor and Marsh, 1963). However, two species described by Park can easily digest unswollen cotton fibres. Whilst other species of Pythium grow well on starch- or maltose-containing media, such as cornmeal agar, Parks species are completely inhibited by these compounds. Suitable media for the cellulolytic species are cellulose agar (Park, 1973), carboxymethyl cellulose agar (Park, 1975) and pieces of filter paper or lense tissue in sterile Petri solution (Park, 1975). These fungi produce at least two pigments: a pink one which resists extraction with normal solvents and a yellow one which is extractable in hot methanol. The colours differ from those found in some cultures of P. torulosum (slightly violet) or P. oligandrum (yellow due to abundant oospores).

 

86a. Pythium fluminum Park var. fluminum - Trans. Br. mycol. Soc. 69: 225. 1977 - Fig. 94.

Colonies on cellulose agar producing little aerial mycelium, peach to flesh coloured. Main hyphae up to 10 m wide, richly branched, often lobed, forming digitate, pectinate or corralloid hyphae at the margin of the colony. Sporangia filamentous, 6-10 m wide, more regularly shaped than the vegetative hyphae. Vesicles globose or ellipsoidal, producing 5-10 zoospores; encysted zoospores 8-12 m diam. Oogonia intercalary, sometimes terminal, with a smooth wall, 25-60 x 15-25 m. Antheridia 1-2 per oogonium, diclinous. Oospores single, (sub)globose, aplerotic, 16-30 m diam, wall 2-4 m thick.

Cardinal temperatures: minimum below 5C, optimum 20C, maximum 27C. Daily growth rate on cellulose agar at 20C: 1.5-2.0 mm.

Discussion.

The colour is due to at least two pigments. In young cultures the pink hue is most obvious, in old cultures it may fade to saffron. Colonies are more yellowish on media with soluble carbon sources such as glucose or cellobiose. Not only the vegetative mycelium but also the antheridia and antheridial stalks are irregular in shape; the oogonia-bearing hyphae and the sporangia are less variable in width. Though this species is related to species like P. dissotocum, P. diclinum, P. coloratum and P. adhaerens, it differs from all of these by its nutritional specialization, pigmentation and characteristic irregularly swollen hyphae. [p. 182]

Fig. 94. - P. fluminum var. fluminum. a. broad tapering hyphae, b. coralliform branching system, c1 -6. various stages in development of oogonia and antheridia (reproduced, with permission, from Park, 1977).

[p. 183]

86b. Pythium fluminum var. flavum Park - Trans. Br. mycol. Soc. 69: 230. 1977.

This variety differs from var. fluminum by its brighter yellow colour on media with cellulose and a slower daily growth rate (0.5-1.0 mm at 20C). It has pure bright yellow to straw pigmentation which is due to the same two pigments found in var. fluminum, but the methanol-extractable yellow component is more represented.

Occurrence and pathogenicity

Both varieties of P. fluminum are only known from certain rivers in Ireland. Nothing is known about their pathogenicity to other organisms. They are difficult to maintain in culture for a prolonged period.

Fig. 95. - P. uladhum. a1-5. oogonia and antheridia (reproduced, with permission, from Park, 1977).

 

87- Pythium uladhum Park - Trans. Br. mycol. Soc. 69: 230. 1977 - Fig. 95.

Colonies on media with cellulose saffron to pale yellow, with little aerial mycelium. Main hyphae up to 6 m wide. Zoosporangia and zoospores not observed. Oogonia terminal on usually short lateral branches, globose, smooth-walled, 25-45 m diam, wall [p. 184] 1-2 m thick. Antheridial cells on branched stalks, 2-4 (-more), partly enwrapping the oogonium, applied laterally. Oospores single, aplerotic or nearly plerotic, globose, 22-40 m diam, thin-walled.

Cardinal temperatures: minimum 5-7C, optimum 20C, maximum 27C. Daily growth rate on cellulose agar at 20C: 4.0-5.5 mm.

No material available.

Discussion

This species differs from P. fluminum in having normal, regular hyphae, terminal oogonia, a larger number of antheridia, lacking sporangia and the different manner of attachment of the antheridia to the oogonia. P. uladhum resembles P. scleroteichum in its sexual structures but differs by its nutritional requirements and yellow pigmentation.

Occurrence and pathogenicity

P. uladhum has only been isolated from streaming water in Ireland. Nothing is known about its pathogenicity. [p. 185]

 

X. DOUBTFUL AND EXCLUDED SPECIES

 

Except in the case of recently described species, morphological details are omitted as these were given in detail by Waterhouse (1968a).

 

Pythium acrogynum Y - Acta microbiol. sin. 13: 117. 1973 - Fig. 96.

Main hyphae up to 7.7 m wide. Sporangia 24-40 (av. 31) m diam, terminal, rarely intercalary, (sub)globose. Zoospores unknown. Oogonia terminal, (sub)globose, papillate, rarely smooth, 18-25 (av. 21) m diam. Antheridia 1, hypogynous; antheridial cells large, 8-15 x 6-14 m (av. 11.5 x 9m). Oospores plerotic, single, 18-23 (av. 20) m diam, wall smooth, 0.8-1.7 (av. 1.5) m thick. Isolated from soil in Wuchang, Hupei, 1964.

Other species with globose hyphal swellings or sporangia and plerotic oospores are P. pleroticum, P. rostratum and P. hypogynum. P. pleroticum has smaller oogonia but more antheridia and these are diclinous. P. rostratum has hypogynous antheridia but differs from P. acrogynum by its typically intercalary oogonia. P. acrogynum seems to be most closely related to P. hypogynum but can be distinguished by its larger, more irregular antheridia and an oogonial wall with only a few papillae. Occasionally occurring papillae are sometimes also formed in other species with smooth oogonia (e.g. P. ultimum).

Fig. 96. - P. acrogynum. a1-6. oogonia, b1-3. hyphal swellings, in b3 germinating (reproduced from Y, 1973).

[p. 186]

Pythium actinosphaerii Brandt - Mber. K. preuss. Akad. Wiss. Berlin 1: 339-400. 1881.

A parasite of Actinosphaerium eichhornii in Germany. Fischer (1892), Butler (1907) and Zopf (1890) believed that this species is not a Pythium.

Pythium afertile Kanouse & Humphrey - Pap. Mich. Acad. Sci. 8:137-138.1927.

Originally isolated from a fly dropped into a dish with Vaucheria sp. near Ann Arbor, Michigan. The features described by Kanouse and Humphrey do not allow separation of this species from other sexually sterile species with filamentous sporangia. Isolates identified as P. afertile were subsequently recorded from Viola sp. in the Netherlands (239), soil in Haiti (64), Gossypium sp. in the Sudan (22, 610), turf grasses in the USA (372), water in Germany (402) and the USSR (634), soil and several plants in New Zealand (816), sugar-cane (1077) and strawberry in Japan (1081); there is no actual evidence that these isolates were identical with the original P. afertile.

Fig. 97. - P. amasculinum. a1 -4. ornamented oogonia, b1 -6. solitary and contiguous hyphal swellings (reproduced from Y, 1973).

 

Pythium amasculinum Y - Acta microbiol. sin. 13: 118. 1973 - Fig. 97.

Main hyphae up to 6.0 m wide. Sporangia terminal or intercalary, (sub)globose, 8.5-20 (av. 15) m diam, or ovoid or limoniform and 13-19 x 10-16 m; contiguous swellings also present. Zoospores unknown. Oogonia terminal or intercalary, globose, ornamented, 15-29 (av. 23.3) m diam, ornamentations rather acute, 1.7-7.7 (av. 4.5) m long and 1.7-4.3 (av. 2.4) m diam at the base. Antheridia lacking. Oospores plerotic, [p. 187] occasionally aplerotic, 13-24 (av. 20.5) m diam, wall 1.3-1.7 m thick. Type Y Y.N. S 69-6 (not seen).

P. amasculinum was originally isolated from soil in Kunming, Yunnan, China. Among the species with ornamented oogonia, P. anandrum and P. oligandrum often lack antheridia. P. anandrum has proliferating sporangia and aplerotic oospores. P. amasculinum differs from P. oligandrum by plerotic oospores and the complete absence of antheridia. P. periplocum also bears some similarity to P. amasculinum but forms 0- 4 often diclinous antheridia. No other records of P. amasculinum are known.

Pythium anguillulae-aceti Sadebeck - Bot. Zentbl. 29: 318. 1887.

A parasite of vinegar ealworms in a vinegar factory in Germany. Identification not possible.

Pythium autumnale Sadebeck - Tagebl. Versamm. dt. Naturf. rzte, Breslau 49: 100. 1876.

Observed in a pot culture of Equisetum prothallia which had been killed by the fungus. Identification not possible.

Fig. 98. - P. betae. a1-9. oogonia and antheridia, b1-9. sporangia, in b8 with vesicle of zoospores, in b9 emptied (reproduced, with permission, from Takahashi, 1972).

 

Pythium betae Takahashi - Ann. phytopath. Soc. Japan 38: 309. 1972 - Fig. 98.

Main hyphae up to 1 m wide. Sporangia globose, oval, intercalary, mostly germinating with germ tubes, rarely with zoospores. Zoospores 6-10 in a vesicle. Hyphal swellings 11.5-20 (av. 13) m diam. Oogonia globose, terminal or intercalary, with 2-3(-6) protuberances, rarely smooth, 14.3-21.5 (av. 18.3) m diam; protuberances rather long, cylindrical, blunt. Antheridia diclinous, rarely monoclinous, 1-2 per oogonium, making lateral contact. Oospores globose, plerotic, rarely aplerotic, thinwalled. [p. 188]

Cardinal temperatures: minimum 15C, optimum 26C, maximum 32C. Daily growth rate on cornmeal agar at 25C: about 8 mm.

According to the illustration, the ornamentation resembles that of P. irregulare and P. spinosum, but P. betae differs from P. irregulare by its plerotic oospores. P. spinosum differs from P. betae by mainly the larger number of protuberances and usually monoclinous antheridia. As influences of the medium on the ratio monoclinous/diclinous antheridia and the number of protuberances cannot be excluded, this species is considered doubtful.

Isolated from sugar-beet in Japan (974, 982).

 

 

Pythium cactacearum Preti - Riv. Patol. veg. 26: 349. 1936.

Isolated from Phyllocactus phyllanthoideus, San Remo, Italy. Identification not possible.

 

Pythium carolinianum Matthews - Stud. Gen. Pythium: 71. 1931.

Isolated from Spirogyra sp., USA. It was found to differ from the other species with proliferating sporangia by its production of catenate hyphal swellings and resting spores. Pythium isolates with proliferous sporangia and no oogonia were repeatedly observed by many investigators and discussed by the present author (1975) under Pythium group P(see p. 12). Of the many crossing experiments with these isolates none resulted in the production of oogonia.

P. carolinianum has also been recorded from vegetable debris in the USA (643) and India (48) and as a causal agent of nursery root rot of Macadamia integrifolia in Costa Rica.

 

Pythium characearum de Wildem. - Annls Soc. belg. Microsc. 20: 119. 1896.

Observed in oogonia of Chara sp. in Switzerland. The antheridia were illustrated as making broad apical contact with the oogonium, thus resembling P. marsipium and some isolates of P. vexans. The oospores are larger than those of P. vexans but of similar size to those of P. marsipium. Nothing is known about the asexual reproduction.

 

Pythium chlorococci Lohde - Tagebl. Vers. dt. Naturf. rzte, Breslau 47: 203. 1874.

Parasitic in a colony of Chlorococcum sp. in Germany. Identification not possible.

Pythium circumdans Lohde - Tagebl. Vers. dt. Naturf. rzte, Breslau 47: 203. 1874.

Observed in fern prothallia, Leipzig, Germany. Identification not possible.

Pythium conidiophorum Jokl - st. bot. Z. 67: 33. 1918.

Parasitic in Spirogyra sp. in Lake Skutary, Albania. The material studied by Jokl was poorly preserved in alcohol; it showed conidia and young oogonia lacking antheridia. The conidia were deciduous in contrast with most other species. P. salpingophorum is a comparable species which also lacks antheridia but does not produce deciduous hyphal swellings. - On the basis of Middletons condensed diagnosis, this species has been identified and reported from alfalfa seedlings in the USA (855, 856) and agricultural soils in Germany, but cultures communicated by the CMI (CBS 326.62 and 165.68) were reidentified as P. salpingophorum.

Pythium connatum Y - Acta microbiol. sin. 13: 118-119. 1973 - Fig. 99.

Main hyphae up to 6.7 m wide. Sporangia terminal or intercalary, (sub)globose, limoniform, pyriform or prolate ellipsoidal, 13-26 (av. 18) m diam, germinating with a germ tube. Zoospores unknown. Oogonia mostly intercalary, sometimes terminal, smooth, 13-23 (av. 19) m diam. Antheridia monoclinous, rarely hypogynous, 1-2 per [p. 189] oogonium; antheridial cells clavate or falcate, 10-21 x 6-7 m. Oospores plerotic, 13-23 (av. 19) m diam, wall 1.7 m thick. Germination not observed.

Fig. 99. - P. connatum. a1-5. oogonia and antheridia, b1-5. hyphal swellings (reproduced from Y, 1973).

P. connatum was originally isolated from soil in Tianjin, Hopei, China. It appears to be closely related to P. hemmianum and P. pleroticum, but has different antheridia.

 

 

Pythium cucurbitacearum Takimoto - Ann. phytopath. Soc. Japan 11: 91. 1941 (nom. inval. Art. 36).

Isolated from Cucumis, Citrullus and Luffa spp. in Japan. Most characteristic are the papillate sporangia and the place of attachment of the antheridia near the oogonial stalk. In this way it differs from P. vexans. P. chamaehyphon has similar antheridia but can be distinguished from P. cucurbitacearum by its non-papillate sporangia. P. cucurbitacearum has also been found to be pathogenic to tomato, Hibiscus, Ipomoea and potato in Japan (806, 807, 974, 975, 984).

Pythium daphnidarum H. E. Petersen - Bot. Tidsskr. 29: 392. 1909 (repr. in Annls mycol. 8: 495. 1910).

Isolated from Daphnia hyalina, Hyalodaphnia cucullata and Bosmina coregoni in Denmark. The fungus belongs to the group of species with filamentous sporangia, but further identification is not possible.

 

Pythium debaryanum Hesse - Pythium debaryanum, ein endophytischer Schmarotzer. Diss. Halle: 14-34. 1874 (as de Baryanum).

From Hesses description and figures it is clear that he did not deal with a pure culture but with a mixture of P. intermedium and another fungus. The deciduous, catenulate [p. 190] conidia belong to P. intermedium, the sexual and sporangial elements to another species which cannot be identified. For further discussion see p. 157. P. debaryanum was originally isolated from Camelina sativa, Spergula aryensis, Trifolium repens and other plants growing in the laboratory at Strasbourg. Under the name P. debaryanum many misidentifications of P. ultimum (e.g. de Bary, 1881; Marchal Ward, 1883) and P. irregulare (e.g. Drechsler, 195 3; Ramos, 1926; Hartley, 1921) have been published; it is also quite possible that P. sylvaticum has often been identified as P. debaryanum. Several strains preserved in the CBS collection as P. debaryanum have been redisposed as follows: P. ultimum: CBS 114.19 from conifer seedlings, CBS 249.28 from Sinningia sp., CBS 378.34 from Trifolium pratense, CBS 305.35 from grass roots, CBS 264.38 from Pinus sylvestris, CBS 398.51 from Lepidium sativum. - P. irregulare: CBS 265.38 from Beta vulgaris. - P. sylvaticum: CBS 633.67 from unknown substrate. - P. dissotocum: CBS 260.30, comm. C.P. Sideris as P. araiosporon.

 

Pythium debaryanum var. viticola Jain - Mag. Nagpur agric. Coll. 25: 8. 1951 (as viticolum; nom. inval. Art. 36).

This variety differs in several respects from P. debaryanum. The sexual elements are more or less similar to those of P. helicoides, P. oedochilum and P. palingenes, but these species have proliferating sporangia. Var. viticola is not identical with P. sylvaticum as suggested by Hendrix and Campbell (1974) because of thick oospore walls, the occurrence of sporangia and the lateral attachment of the antheridia to the oogonia.

 

Pythium debaryi (Walz) Raciborski - Rozpr. Wydz. mat.-przyr. pol. Akad. Umiejęt. 24: 8. 1891 = Saprolegnia debaryi J. Walz - Bot. Ztg 28: 545. 1870.

Observed in cells of Spirogyra densa near Kiev. Identification not possible. Probably not a Pythium.

Hyphomyces destruens-equi de Haan & Hoogkamer - Arch. wiss. prakt. TierheilKde 29: 395.1903.

This species was isolated from horse skin lesions (De Haan, 1902, and l.c.). A formal description was never given as no sporulation was observed. The fungus was only recognized as a Phycomycete, possibly belonging to Mortierella (Bridges and Emmons, 1961) and causing a swamp cancer of horses. Austwick and Copland (1974) placed portions of colonies growing on Sabouraud-glucose agar into sterile water to which a small piece of rotten maize silage had been added. After 2 days incubation at 25C, sporangia developed and biflagellate zoospores were discharged in an Pythium-like manner. Further work will be necessary to establish the true nature of this fungus.

H. destruens-equi has been recorded from lesions of horses in Indonesia (333a, 333b, 333c), the USA (98a), Japan (20a), Australia (435a) and Papua-New Guinea (43).

 

Pythium diacarpum Butler - Mem. Dep. Agric. India, bot Ser. 1(5): 80. 1907.

Typical features are the long, often wavy or helicoid discharge tubes and the very slow growth. In this respect it differs from the many isolates with proliferating sporangia. Only known from the original record from vegetable debris in Germany.

 

Pythium dichotomum Dangeard - Annls Sci. nat., Bot., Sr. 7, 4: 313. 1886.

Probably not a Pythium, identification not possible.

Pythium dictyosporum Raciborski - Rozpr. Wydz. mat.-przyr. pol. Akad. Umiejęt. 1891: 283-298; ibid. 24: 1-8. 1892; emend. Sparrow - Mycologia 23: 199. 1931 = Nematosporangium dictyosporum (Racib.) Schrter in de Wildeman - Annls Sci. belg. Microsc. 19: 206. 1895; Engler & Prantl, Nat. PflFam. 1(1): 104. 1897 = [p. 191] Nematosporangium dictyosporum (Racib.) Jaczewski - Opredelitel Gribov, I. Fikomitsety, p. 96. 1931 (as dictyospermum).

Originally observed in Spirogyra spp. in Poland and subsequently in France and the USA by Matthews (1931) and Sparrow (1931, 1933) and also in Vaucheria, by Middleton (1943). P. dictyosporum has ornamented oospores, a feature only known in one other species of the genus, P. pythioides. The latter has globose sporangia and is not closely related to P. dictyosporum. The ornamentation consists of small projections in P. pythioides and a reticulate gelatinous layer in P. dictyosporum.

P. dictyosporum infects Cucumis sativus, Rhizoclonium sp., Tolypothrix sp. and Oedogonium sp. (914, 918).

 

Pythium echinocarpum S. Ito & Tokunaga - J. Fac. Agric. Hokkaido Univ. 32:210. 1933.

Originally isolated from seedlings of Oryza sativa in Japan. It resembles P. hydnosporum in the size of the oogonia and oospores, the aplerotic oospores and the ornamentation; the thickness of the oospore walls differs slightly, and stalked antheridia are not common in P. hydnosporum. The few reports included rice in Japan (188) and cucumber in Malaysia (556).

 

Pythium elongatum Matthews - Stud. Gen. Pythium: p. 106. 1931.

Originally isolated from cottonfield soil in N. Carolina, USA. P. elongatum was distinguished from other species with globose sporangia but lacking oogonia, by its long discharge tubes, the variable sporangia and the hyphal swellings. Only a few subsequent records are known: from water in Germany (402), soil in England (29, 30) and Iraq (13), and roots and soil in Taiwan (424, 425, 1082).

 

Pythium entophyton Pringsheim - Jb. wiss. Bot. 1: 288. 1858 = Lagenidium entophytum (Pringsheim) Zopf - A. Schenk, Handb. Bot. 4: 271. 1890.

P. entophytum sensu Schenk (1859) was reidentified as P. tenue by Gobi (1899-1900).

 

Pythium equiseti Sadebeck - Verh. bot. Ver. Brandenb. 16: 116-125. 1874. Bot. Ztg 33: 639-645. 1875; Sber. Ges. naturf. Freunde Berl. 1875: 148-151.

Reported as a parasite of Equisetum prothallia in Germany. Identification not possible.

 

Pythium fecundum Wahrlich - Ber. dt. bot. Ges. 5: 243. 1887.

Originally isolated by De Bary in 1884 from sediment in a small glacier brook of the Rhne glacier in Switzerland and subsequently studied by Wahrlich. Two or three oospores were often present in a more or less elongate oogonium, but not all of these matured. Sometimes 2 or 3 oogonia developed in such close connection that they formed twin or triplet oogonia. Some of these oospores developed vegetative hyphae without reaching maturity. Fisher (1892) and Butler (1907), followed by Matthews (1931) and Middleton (1943), considered this species to be synonymous with P. monospermum; but in P. monospermum multiple oospores are never observed and the oospores are provided with much thicker walls. Multiple oospores occur occasionally in P. violae and commonly in P. multisporum. No other records of P. fecundum are known.

Pythium ferax de Bary - Bot. Ztg 39: 562. 1881.

Identification not possible.

 

Pythium fimbriatum De-la-Rue - Buyll. mosk. Obshch. Ispyt. Prir. (Bull. Soc. Nat. Moscou) 42: 469. 1869 (nomen nudum).

On insects in water. [p. 192]

 

Pythium fragariae Takahashi & Kawase -Ann. phytopath. Soc. Japan 30:183.1965 (nom. inval. Art. 37).

Isolated from Fragaria chiloensis in Japan. Apparently related to P. paroecandrum but differing by thicker oospore walls. It differs from the otherwise similar P. hemmianum by having smaller antheridia which make apical contact.

 

 

Pythium ? gibbosum de Wildeman - Annls Soc. belg. Microsc. 20: 121. 1896 (nom. provis. ).

Placed hesitantly in Pythium, found in oogonia of Chara sp. in Switzerland. Identification not possible.

Pythium globosum Schenk - Verh. phys.-med. Ges. Wrzb. 9: 25. 1859 = Lagenidium globosum (Schenk) Lindsted - Synops. Saproleg. Beobachtungen, Berlin: 54. 1872.

Observed in Mougeotia sp. in Germany. Possibly belonging to Myzocytium (Von Minden, 1912; Sparrow, 1960) or Pythium entophytum (Waterhouse, 1968a).

 

Pythium globosum sensu Walz - Bot. Ztg 28: 555. 1870.

A combination of P. globosum Schenk and P. proliferum Schenk, published with emended description. Possibly a Myzocytium.

Pythium gracile Schenk - Verh. phys.-med. Ges. Wrzb. 9: 13-20. 1859 = Nematosporangium gracile (Schenk) Schrter- Engler & Prantl, Nat. PflFam. 1(1): 104. 1879 = Nematosporangium gracile (Schenk) Jaszewski - Opredelitel Gribov, I. Fikomitsety, p. 96. 1931.

Observed in Spirogyra, Cladophora and Nitella spp. in Germany. Without observation of oogonia no positive identification is possible. Possibly a heterothallic species. For further discussion see P. monospermum, P. diclinum and P. flevoense. P. gracile has been reported recently from foci of granular dermatitis in horse (436a).

 

Pythium horinouchiense Hirane - Trans. mycol. Soc. Japan 2: 84. 1960 (nom. inval. Art. 37).

This species is difficult to place as no sporangia or hyphal swellings were described. The sexual organs bear some similarity to P. irregulare but the oogonia are larger. It caused snow-blight of Triticum aestivum, Hordeum sativum, Eleusine indica, Syntherisma sanguinale, Trifolium repens and Raphanus sativus in Japan.

Pythium hydrodictyorum de Wildeman - Annls Soc. belg. Microsc. 21: 24. 1897.

Parasitic in Hydrodictyon utriculatum (reticulatum) in Indonesia. Identification not possible.

 

Pythium imperfectum Cornu - Annls Sci. nat., Bot., Sr. 5, 15: 13. 1872.

Identification not possible.

Pythium imperfectum Hhnk- Verff. Inst. Meeresforsch. Bremerh. 2: 72.1953 (non Cornu 1872).

The description is insufficient to distinguish the species from other sexually sterile species with filamentous slightly swollen sporangia.

 

Pythium incertum Renny ex W.G. Sm. - Gdnrs Chron., N. S. 5 (125): 656.1876; ibid. 6 (131): 10. 1876; Justs bot. Jber. 1876: 134.

Observed on leaves of Cuphea sp. Identification not possible. [p. 193]

Fig. 100. - P. jirovecii. a1-3. oogonia, b. zoosporangia, c. zoospores (redrawn from Cejp, 1955; magnification not indicated).

 

Pythium jirovecii Cejp - Cslk Parasitol. 2: 15. 1955 - Fig. 100.

Main hyphae irregular, up to 15 m wide. Sporangia globose or ellipsoidal, non-proliferating, 50 x 40 m; zoospores 4-6 x 3-4 m. Oogonia 20 m diam with an irregular, angular wall. Antheridia hypogynous. Oospores aplerotic, thin-walled. The antheridia are described as hypogynous but illustrated as being possibly diclinous or of uncertain origin. In this respect, P. jirovecii would differ from P. pulchrum, P. hypogynum and P. rostratum. The irregularly angular shape of the oogonial wall also separates P. jirovecii from these species and from P. iwayamai. A similar irregular shape sometimes occurs in P. irregulare, but this species has mostly monoclinous antheridia and often cylindrical protuberances on the oogonial wall. P. daphnidarum has filamentous sporangia. P. jirovecii was observed as a parasite of Daphnia pulex in Czechoslovakia.

 

Pythium kunmingense Y - Acta microbiol. sin. 13: 119-120. 1973 - Fig. 101.

Main hyphae up to 8.6 m wide. Sporangia (sub)globose, ovoid or limoniform, terminal or intercalary, 13-23 (av. 19) m diam, with a smooth, rarely spiny wall. Zoospores unknown. Oogonia (sub)globose or limoniform, terminal or intercalary, 15-26 (av. 21) m diam, ornamented, rarely smooth. Ornamentations papilliform, 2.5-14 m long and 1.7-2.5 m diam at the base. Antheridia 1-3 per oogonium, mostly monoclinous, occasionally diclinous; antheridial cells clavate, curved, vermiform or sickle-shaped, 13-19 x 5.2-6.8 m. Oospores plerotic, 10-24 (av. 19) m diam, wall 0.8-2.0 m thick.

The other species with globose, non-proliferating sporangia, ornamented oogonia and plerotic oospores and oogonia smaller than 30 m diam, are P. acanthicum, P. mamillatum, P. spinosum and P. echinocarpum. The latter can be distinguished from P. kunmingense by the occasional occurrence of hypogynous antheridia, and from P. spinosum by its more regular ornamentation and larger numbers of finger-like protuberances on the oogonia. P. acanthicum has a more regular ornamentation of conical subacute protuberances. P. mamillatum has often curved, obtuse oogonial projections. P. kunmingense resembles P. irregulare, but the latter has aplerotic oospores and always [p. 194] finger-like ornamentations, while in P. kunmingense they are illustrated as conical or digitate, acute and obtuse. P. kunmingense was isolated from soil in Kunming, Yunnan, China. No other records are known.

Fig. 101. - P. kunmingense. a1-5. oogonia and antheridia. b1-4. sporangia (reproduced from Y, 1973).

 

Pythium laterale Pringsheim - Jb. wiss. Bot. 9: 226. 1873 (nom. nud.).

Pythium marchantiae Nicolas - Bull. trimest. Soc. mycol. Fr. 43: 119-121. 1927 (1928?).

Observed causing discoloration of Marchantia polymorpha, France. Middleton (1943) regarded this species as synonymous with P. debaryanum, but the insufficient description does not agree with any description of P. debaryanum or other species. Identification not possible.

 

Pythium muscae Dangeard - Botaniste 22: 452. 1931.

Covering a fly in water. Probably a mixture of different organisms, the zoosporangia observed possibly belonging to a Pythium sp.

 

Pythium nelumbii Takahashi & Ohuchi - Ann. phytopath. Soc. Japan 30:189.1965 (nom. inval. Art. 37).

Causing rhizome-rot of Nelumbo nucifera. It resembles P. arrhenomanes in the type of antheridia but differs in having globose as well as filamentous inflated sporangia. In the diagnosis only the inflated sporangia and conidia germinating by germ tubes are [p. 195] mentioned, but in the discussion and illustration globose sporangia are mentioned and depicted. P. nelumbii was shown to be pathogenic to lotus (974, 980).

Fig. 102. -P. paddicum. a1-5. oogonia and antheridia, a6. germinating oospore, b1-4. sporangia, in b4 discharging zoospores (reproduced from Hirane, 1960).

Pythium paddicum Hirane - Trans. mycol. Soc. Japan 2: 85. 1960 (nom. inval. Art. 37) - Fig. 102.

P. paddicum seems to be close to P. polypapillatum, P. anandrum and P. helicandrum, but the sporangia are smaller than in P. helicandrum and P. anandrum, the antheridal stalks do not entwine the oogonial stalk as in P. helicandrum and, in contrast with P. anandrum, antheridia are always formed. The ornamentations in P. paddicum are markedly different from those of P. polypapillatum.

P. paddicum has only been recorded from Japan where it caused snow-blight of Triticum aestivum, Hordeum vulgare, Avena sativa, Astragalus sinicus, Oryza sativa, Alopecurusfulvus, Lactuca debilis, Cardamineflexuosa, Nasturtium pa lustre, Raphanus sativus, Brassica rapa, B. sinensis, and Allium cepa.

 

 

Pythium palmivorum Butler - Mem. Dep. Agric. India, bot Ser. 1: 82-84. 1907 = Phytophthora palmivora (Butler) Butler - Scient. Rep. agric. Res. Inst. Pusa 1918-19: 82. 1919.

This species may cause some confusion as the zoospores occasionally cluster at the mouth of the sporangium (Waterhouse, 1956).

 

Pythium plerosporon Sideris - Mycologia 24: 50. 1932.

Isolated from diseased roots of tobacco in Kentucky, USA. The original description and figures do not allow identification (cf. also P. rostratum). [p. 196]

 

Pythium pleroticum T. Ito - J. Jap. Bot. 20: 59. 1944.

Isolated from water in Japan. The species shows some similarity to P. conidiophorum and P. hemmianum. In P. hemmianum the oogonia are smaller, while in P. conidiophorum the antheridia appear to be absent and hyphal swellings are deciduous and smaller. Sporangia and zoospores have never been observed. P. pleroticum has also been recorded from water in the USSR (634).

 

Pythium polysporum Sorokin - Trudy Obshch. Estest. imp. Kazan. Univ. 2: 23.1873 = Nematosporangium polysporum (Sorokin) Jacz. - Opredelitel Gribov, I. Fikomitsety, p. 98. 1931.

Isolated from flies in water in Russia. The species does not belong in Pythium (Butler, 1907; Matthews, 1931; Middleton, 1943; Waterhouse, 1967).

 

Pythium proliferum Schenk - Verh. phys.-med. Ges. Wrzb. 9: 20-25.1859 [p. non de Bary 1860] = Myzocytium proliferum (Schenk) Schenk - Verh. phys.-med. Ges. Wrzb. 9: 20-25. 1859 = Lagenidium globosum (Schenk) Lindstedt - Synops. Saproleg. Beobachtungen, Berlin: 54. 1872.

 

Lucidium pythioides Lohde - Tagebl. Vers. dt. Naturf. rzte, Breslau 47: 205.1874.

Although Lucidium Lohde is generally regarded as synonymous with Pythium, this species probably does not belong in Pythium as the zoospores are formed within the sporangium and are released in a vesicle. A parasite of young Lepidium sativum plants, which are killed within 2-3 days.

 

Pythium reptans de Bary - Jb. wiss. Bot. 2: 188-189. 1860.

Observed in Bangia atropurpurea, Spirogyra nitida, Heeriana sp., Vaucheria sp. and on dead insects in water. Forming only filamentous, non-inflated sporangia. In a footnote De Bary regarded this species as synonymous with P. gracile Schenk. De Bary (1881) also identified an isolate which formed oogonia as P. reptans, but this was reidentified as P. monospermum (slides preserved at BM).

 

Pythium sadebeckianum Wittmack - Mitt. Ver. Frd. Moorkult. 10: 83. 1892.

Causing stem-rot of peas in Germany. Identification not possible.

Saprolegnia schachtii Frank - Krankh. d. Pflanzen, Breslau: p. 385. 1880.

Fischer (1892) regarded this species as synonymous with P. debaryanum. This is not justified, as perforated oogonial walls are not known in Pythium.

 

Pythium sinense Y - Acta microbiol. sin. 13: 121. 1973 - Fig. 103.

Main hyphae up to 7.7 m wide. Sporangia sessile, (sub)globose, ellipsoidal, ovoid or pyriform, 14-52 x 14-38 m (av: 31 x 24 m). Zoospores reniform, biciliate, 6-9.5 (av. 7.3) m diam. Oogonia terminal, rarely intercalary, (sub)globose, ornamented, 17-35 (av 24.5) m diam; ornamentations acute, 2.8-5.6 (av. 4) m long and 1.7-2.6 (av. 2.3) m diam at the base. Antheridia terminal, diclinous, rarely monoclinous, 0-2 per oogonium, clavate or vermiform, 12-28 x 8-14 m. Oospores globose, rarely ellipsoidal, aplerotic, rarely plerotic, 14-27 (av. 21.5) m diam, wall 1.4-3 (av. 2.3) m thick. Isolated from soil in Peking, China.

P. sinense is close to or possibly identical with P. oligandrum. The oospore wall in P. sinense is somewhat thicker and the ornamentations shorter than in P. oligandrum. The sporangial elements and the sexual apparatus are very similar in both species. [p. 197]

Fig. 103. P. sinense. a1-5. oogonia and antheridia, b1-5. sporangia, c. encysted zoospores (reproduced from Y, 1973).

 

Phytophthora stellata Shanor - J. Elisha Mitchell scient. Soc. 54: 155, 1938 (nom. inval. Art. 36).

Main hyphae up to 7 m wide. Sporangia obpyriform, oval or elongate, occasionally proliferating (according to the original illustration), when terminal 80.5-116 x 36 m (mostly 86.6 x 27 m). Encysted zoospores 10-14.5 m diam. Oogonia on short side branches, globose, 15.5-22.5(-30) m diam, with acute ornamentations up to 3.5 m long. Antheridia single, monoclinous, sometimes diclinous; antheridial cells long, club-shaped, 7.0-10.5 m diam, mostly making contact near the oogonial stalk. Oospores nearly plerotic, 13.8-17.2 (mostly 14.3-15.4) m diam.

Ph. stellata does not belong to Phytophthora but to Pythium. Of the other species which have ornamented oogonia and proliferating sporangia, P. megalacanthum has larger oogonia, P. anandrum mostly parthenogenetically developing oospores, P. helicandrum apparently has no proliferating sporangia and its antheridial stalks entwine the oogonial stalks, while P. paddicum and P. polypapillatum have smaller sporangia and different oogonial projections. Ph. stellata must be recognized as a distinct species but cannot be validated in the absence of suitable type material. It has only been recorded from petals of Rhododendron maximum in the USA.

Pythium subtile Wahrlich - Arb. St. Petersb. naturf. Ges. (Trudy imperat. petrograd. Obshchestva Estvestvoispyt.) 19: 23. 1889 = Nematosporangium subtile (Wahrlich) Jaszewski - Opredelitel Gribov, I. Fikomitsety, p. 97. 1931.

Identification not possible. [p. 198]

 

 

Pythium teratosporon Sideris - Mycologia 24: 40. 1932.

In a foot-note Sideris (1932) transferred this species to Phytophthora. Middleton (1943) considered it to be Ph. drechsleri Tucker. Observed on Cajanus indicus and isolated from Spinacia oleracea.

 

 

Pythium thalassium Atkins - Trans. Br. mycol. Soc. 38: 31. 1955.

Differs from all other known species by its proliferous filamentous sporangia. It is therefore doubtful whether it belongs to Pythium. Observed on eggs of Pinnotheres pisum in Cornwall.

 

Pythium tuberculorum (Vuill.) Lechtova-Trnka - Etude sur les Bactries des Lguminoses et Observations sur quelques Champignons parasites des Nodosits. Thse, Paris: 453. 1931 = Cladochytrium tuberculorum Vuill. - Annls Sci. agron. Fr. Etr. 5: 121. 1888.

This species was originally found in root nodules of Galega officinalis and Medicago disciformis. Vuillemin (1905) already considered it to be a Pythium species although he mentioned uniflagellate zoospores. This fungus has globose sporangia and smooth oogonia, mono- and diclinous antheridia and reticulate oospores.

 

Pythium utriforme Cornu - Annls Sci. nat., Bot., Sr. 5. 15: 13. 1872.

Identification impossible.

 

Pythium vitis Serbinov apud Jaczewski - Opredelitel Gribov, I. Fikomitsety, p. 98. 1931.

In seedlings of Vitis vinifera. Identification not possible.

 

Pythium zeae K. B. Deshpande & K. S. Deshpande - Sydowia 18: 33 (1964). 1965.

Though the tubes containing the type culture received from the authors were broken during transport, they contained only Fusarium sp. From the description and figures it is also evident that the name was based on a mixture containing Fusarium sp.

 

ACKNOWLEDGEMENTS

The author is much indebted to Mr. Ren P. W. M. Jacobs for his efficient assistance during the completion of the manuscript, particularly by checking and supplementing the references. Dr. W. Gams and Mr. Ren P. W. M. Jacobs edited the text and are thanked most sincerely for their helpful criticism. The author is also grateful to Dr. Grace M. Waterhouse and Dr. D. Jean Stamps for their encouragement and help during the years of research and their comments on the manuscript. Dr. Connie A. N. van Oorschot is acknowledged for correcting the English text, Miss J. B. Pannebakker for technical assistance and photography, Dr. R. A. Samson and Dr. J. A. Stalpers for taking the SEM pictures, Miss I. ten Hoedt, Mr. Ren P. W. M. Jacobs and Mr. D. Dutscher for inking many drawings.

The authors and copyright holders of the figures 25, 33, 35, 36, 41, 46, 47, 56, 62, 66, 69, 79, 81, 85, 88, 92, 94, 95 and 98 are acknowledged for permitting reproduction.

 

 

REFERENCES

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2. ADAIR, C., 1972 - Ecological relationships of Pythium species in the rhizosphere of sugarcane - and possible significance in yield decline. - Hawaii. Plrs Rec. 58 (17): 213-240.

3. ADERUNGBOYE, F. O. & ESURUOSO, O. F., 1976 - Ecological studies of Pythium splendens on oil palm. - Pl. Soil 44: 397-406.

4. AGATI, J. A., 1931 - Studies on the root rot of the sugar cane seedlings in the nursery. - Philipp. J. Agric. 2: 1-26.

5. AGNIHOTRI, V. P., 1969 - Production and germination of appressoria in Pythium irregulare. - Mycologia 61: 967-980.

6. AGNIHOTRI, V. P. & VAARTAJA, O., 1967a - Effects of amendments, soil moisture and temperature on germination of Pythium sporangia under the influence of soil mycostasis. - Phytopathology 57: 1116- 1120.

7. AGNIHOTRI, V. P. & VAARTAJA, O., 1967b - Root exudate from red pine seedlings and their effects on Pythium ultimum. - Can. J. Bot. 45: 1031-1040.

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9. AGNIHOTRI, V. P. & VAARTAJA, O., 1970 - Effect of seed exudates of Pinus resinosa on the germination and on the population of Pythium irregulare in the soil. - Pl. Soil 32: 246-249.

10. AHRENS, C., 1971a - Eine neue Pythium-Art aus dem Libanon. - Z. PflKrankh. PflSchutz 78: 175-180.

11. AHRENS, C., 1971b - Untersuchungen zur Taxonomie and nur geographischen Verbreitung der Gattung Pythium Pringsheim. - Diss. Univ. Bonn.

12. AKAI, S., TAKAHASHI, M. & TAKEUCHI, T., 1956 - Studies on the mechanism of damping-off resistance in the seedlings of cucurbitaceous plants. 1. Anatomical observation of the invasion of Pythium fungi into hosts. - Forsch. PflKrankh., Kyoto 6: 1-5.

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166. CHOHAN, J. S. & IQBAL SINGH, 1972 - Two new fungi associated with root rot and wilt in bhindi (Abelmoschus esculentus) in India. - Indian J. Mycol. Pl. Path. 2: 175.

167. CHONA, B. L., 1958 - Some diseases of sugarcane reported from India in recent years. - Indian Phytopath. 11: 1-9.

168. CHOU, L. G. & SCHMITTHENNER, A. F., 1974 - Effect of Rhizobium japonicum and Endogone mosseae on soybean root rot caused by Pythium ultimum and Phytophthora megasperma var. sojae. - Pl. Dis. Reptr 58: 221-225.

169. CHOWDHERY, H. J. & RAI, J. N., 1980 - Microfungi from mangrove swamps of West Bengal, India. II. Some new records of aquatic fungi. - Nova Hedwigia 32: 237-242.

170. CHU, H. T., HSU, S. C. & LIU, Y. T., 1966 - Study on the pathological causes of poor ratoon standing of sugar cane. - Rep. Taiwan Exp. Stn 43: 1-9.

171. CICCARONE, A., 1953 - Disease outbreaks on economic plants in Italy. - Pl. Prot. Bull. F. A. O. 1: 49-51.

172. COGNE, M., 1960 - Premires observations sur les fontes de semis de cotonniers la Station de Bambari. - Phytiat.-Phytopharm. 9: 207-222.

173. COKER, W. C., 1923 - The Saprolegniaceae. - Univ. N. Carol. Press, Chapel Hill, 201 pp.

174. COKER, W. C. & PATTERSON, P. M., 1927 - A new species of Pythium. - J. Elisha Mitchell scient. Soc. 42: 247-250.

175. COLT, W. M. & ENDO, R. M., 1972 - Ultrastructural changes in Pythium aphanidermatum zoospores and cysts during encystment, germination and penetration of primary lettuce roots. - Phytopathology 62: 751 (Abs.).

176. CONNERS, I. L., 1935 -14th Annual report of the Canadian Plant Disease Survey. - 116 pp. (mimeographed).

177. COOK, M. T., 1939 - Enfermedades de la plantas econmicas de las Antillas. - Monogr. Univ. P. Rico, Ser. B, 4: 530 pp.

178. COOK, W. R. I. & COLLINS, W. B., 1937 - A Pythium wilt of Primula caused by Pythium spinosum. - Trans. Br. mycol Soc. 21: 29-33.

179. COOKE, W. B., 1969 - Fungi in soils over which digested sewage sludge has been spread. - Mycopath. Mycol. appl. 39: 209-229.

180. COOPER, W. E. & CHILTON, S. J. P., 1949 - Antibiotics of Actinomyces strains to Pythium arrhenomanes, P. ultimum and Rhizoctomia solani. - Phytopathology 39: 5 (Abs.).

181. COX, R. S., 1969 - Control of Pythium wilt of chrysanthemum in south Florida. - Pl. Dis. Reptr 53: 912-913.

182. CROOKS, K.M., 1937 - Studies on Australian Phycomycetes. - Proc. R. Soc. Vict. 2, 49: 206-232.

183. CSINOS, A., 1979 - Non-parasitic pathogenesis of germinating tomato by Pythium myriotylum. - Can. J. Bot 57: 2059-2063.

184. CSINOS, A. & HENDRIX, J. W. 1978 - Parasitic and non-parasitic pathogenesis of tomato plants by Pythium myriotylum. - Can. J. Bot. 56: 2334-2339.

185. CUNNINGHAM, D. D., 1897 - On certain diseases of fungal and algal origin affecting economic plants in India. - Scient Mem. Med. Offrs Army India 10: 95.

186. CUSHING, R. L., KIESSELBACH, T. A. & WEBSTER, O. J., 1940 - Sorghum production in Nebrasca. - Bull. Neb. agric. Exp. Stn 329: l-58.

187. DANGEARD, P. A., 1890-1891 - Recherches histologiques sur les champignons. - Botaniste 2: 63-150.

188. DARKER, G. D., 1940 - A brief host index of some plants pathogens and virus diseases in eastern Asia. - Pl. Dis. Reptr, Suppl. 122: 94-123.

189. DASTUR, J. F., 1935 - Diseases of pan (Piper betle) in the central provinces. - Proc. Indian Acad. Sci. 1: 778-815.

190. DAVISON, E. M. & BUMBIERIS, M., 1973 - Phytophthora and Pythium spp. from pine plantations in South Australia. - Aust. J. biol. Sci. 26: 163-169.

191. DEACON, J. W., 1976a - Studies on Pythium oligandrum, an aggressive parasite of other fungi. - Trans. Br. mycol. Soc. 66: 383-391.

192. DEACON, J. W., 1976b - Biological control of take-all by Phialophora radicicola Cain. - Boll. OEPP 6: 297-308.

193. DEACON, J. W., 1979 - Cellulose decomposition by Pythium and its relevance to substrate-groups of fungi. - Trans. Br. mycol. Soc. 72: 469-477.

194. DEACON, J. W. & HENRY, C. M., 1978 - Mycoparasitism by Pythium oligandrum m and P. acanthicum. - Soil Biol. Biochem. 10: 409-416.

195. DFAGO, G., CHILD, J. J. & HASKINS, R H., 1969 - Induction de loognse par les antibiotiques polyniques et interaction avec le cholestrol chez un Pythium sp. PRL 2142. - Can. J. Microbiol. 15: 509-514.

196. DFAGO, G. & KERN, H., 1975 - Uptake and transport of cholesterol by Pythium paroecandrum. - Phytopath. Z. 84: 34-46.

197. DEIGHTON, F. C., 1936 - Mycological work. - Rep. Dep. Agric. Sierra Leone 1935: 22-26.

198. DIDDENS, H. A., 1931 - Onderzoekingen over den vlasbrand, veroorzaakt door Pythium megalacanthum. - Diss. Univ. Amsterdam, 127 pp.

199. DIDDENS, H. A., 1932 - Untersuchungen ber den Flachsbrand, verursacht durch Pythium megalacanthum. - Phytopath. Z. 4: 291-313.

200. DISSMANN, E., 1927 - Vergleichende Studien zur Biologie and Systematik zweier Pythium Arten. - Arch. Protistemk. 60: 142-192.

201. DODGE, B. O. & SWIFT, M. E., 1932 - Black stem rots and leaf spot of Pelargonium. - Jl N. Y. bot. Gdn 33: 97-103.

202. DOIDGE, E. M. & BOTTOMLEY, A. M., 1931 - A revised list of plant diseases occurring in South Africa. - Mem. bot. Surv. S. Afr. 11: 1-78.

203. DOMSCH, K. H. & GAMS, W., 1968 - Die Bedeutung vorfruchtabhngiger Verschiebungen in der Bodenmikroflora. 2. Antagonistische Einflsse auf pathogene Bodenpilze. - Phytopath. Z. 63: 165-176.

203a. DOMSCH, K. H., GAMS, W. & ANDERSON, T.-H., 1980 - Compendium of soil fungi. - Academic Press, London, New York. 2 vols, 860 + 405 pp.

204. DOMSCH, K. H., GAMS, W. & WEBER, E., 1968 - Der Einflu verschiedener Vorfrchte auf das Bodenpilzspektrum in Weizenfeldern. - Z. PflErnhr. Bodenk. 119: 134-149.

205. DRECHSLER, C., 1925a - Root rot of peas in the middle-Atlantic states in 1924. - Phytopathology 15: 110-114.

206. DRECHSLER, C., 1925b - Pythium infection of cabbage heads. - Phytopathology 15: 482-485.

207. DRECHSLER, C., 1925c - The cottony leak of cucumbers caused by Pythium aphanidermatum. - J. agric. Res. 30: 1035-1042.

208. DRECHSLER, C., 1926 - The cottony leak of eggplant fruit caused by Pythium aphanidermatum. - Phytopathology 16: 47-49.

209. DRECHSLER, C., 1927 - Pythium ultimum and Pythium debaryanum. - Phytopathology 17: 54-55 (Abs.).

210. DRECHSLER, C., 1928 - Pythium arrhenomanes n. sp., a parasite causing maize root rot. - Phytopathology 18: 873-875.

211. DRECHSLER, C., 1930 - Some new species of Pythium. - J. Wash. Acad. Sci. 20:398-418.

212. DRECHSLER, C., 1934 - Pythium scleroteichum n. sp. causing mottle necrosis of sweet potatoes. - J. agric. Res. 49: 881-890.

213. DRECHSLER, C., 1936 - Pythium graminicolum and P. arrhenomanes. - Phytopathology 26: 676-684.

214. DRECHSLER, C., 1938 - Two hyphomycetes parasitic on oospores of root rotting oomycetes. - Phytopathology 28: 81-103.

215. DRECHSLER, C., 1939a - Several species of Pythium causing blossom-end rot of watermelon. - Phytopathology 29: 391-422.

216. DRECHSLER, C., 1939b - Three species of Pythium with large oogonial protuberances. - Phytopathology 29: 1005-1031.

217. DRECHSLER, C., 1940 - Three species of Pythium associated with root rots. - Phytopathology 30: 189-213.

218. DRECHSLER, C., 1941 - Three species of Pythium with proliferous sporangia. - Phytopathology 31: 478-507.

219. DRECHSLER, C., 1943 - Two species of Pythium occurring in southern states. - Phytopathology 33: 261-299.

220. DRECHSLER, C., 1946a - Zoospore development from oospores of Pythium ultimum and Pythium debaryanum and its relation to rootlet-tip discoloration. - Pl. Dis. Reptr 30: 226-227.

221. DRECHSLER, C., 1946b - Several species of Pythium peculiar in their sexual development. - Phytopathology 36: 781-864.

222. DRECHSLER, C., 1947 - Germination of oospores op Pythiurn butleri and Pythium tardicrescens. - Phytopathology 37: 438-439 (Abs.).

223. DRECHSLER, C., 1949 - Longevity of some Pythium species in maize-meal agar cultures. - Phytopathology 39: 503 (Abs.).

224. DRECHSLER, C., 1950 - A Pythium with stout oogonial spines and coiled antheridial branches. - Bull. Torrey bot. Club 77: 442-461.

225. DRECHSLER, C., 1952a - Production of zoospores from germinating oospores of Pythium ultimum and Pythium debaryanum. - Bull. Torrey bot. Club 79: 431-450.

226. DRECHSLER, C., 1952b - Bean stem rot in Maryland and Delaware caused by several Pythium species. - Pl. Dis. Reptr 36: 13.

227. DRECHSLER, C., 1953 - Development of Pythium debaryanum on wet substratum. - J. Wash. Acad. Sci. 43: 213-225.

228. DRECHSLER, C., 1955 - Production of zoospores from germinating oospores of Pythium butleri. - Sydowia 9: 451-463.

229. DRECHSLER, C., 1960a - A Pythium causing stem rot of tobacco in Nicaragua and Indonesia. - Sydowia 11: 4-120.

230. DRECHSLER, C., 1960b - Two root rot fungi closely related to Pythium ultimum. Sydowia 14: 106-114.

231. DUDKA, I. A., 1970 - (Peculiarities of mycoflora of the Ukrainian Polessye basins.) - Ukr. Bot. Zh. 27: 105-107.

232. DUERDEN, H., 1943 - Note on the occurrence of Pythium mamillatum in Britain. - Trans. Br. mycol. Soc. 26: 15.

233. DURRELL, L. W. & SHIELDS, L. M., 1960 - Fungi isolated in culture from soils of the Nevada test site. - Mycologia 52: 636-641.

234. EBBELS, D. L. & ALLEN, D. J., 1979 - A supplementary and annotated list of plant diseases, pathogens and associated fungi in Tanzania. - Commonw. Mycol. Inst. Kew, Phytopath. Pap. 22: 89 pp.

235. ECKERT, J. W. & TSAO, P. H., 1962 - A selective antibiotic medium for isolation of Phytophthora and Pythium from plant roots. - Phytopathology 52: 771-777.

236. EDGERTON, C. W. & MORELAND, C. C., 1921 - Fungi and cane germination. - Sugar 23: 16-17.

237. EDSON, H. A., 1915 - Rheosporangium aphanidermatum, a new genus and species of fungus parasitic on sugar beets and radishes. - J. agric. Res. 4: 279-292.

238. EDSON, H. A. & WOOD, J. J., 1937 - Diseases of plants in the USA in 1936. - Pl. Dis. Reptr, Suppl. 103: 123-244.

239. EEK, T. VAN, 1937 - Wortelrot van Viola tricolor. - Diss. Univ. Amsterdam, 83 pp.

240. EEK, T. VAN, 1938 - Root-rot of Viola tricolor maxima. - Phytopath. Z. 11: 217-282.

241. EL-HELALY, A. F., IBRAHIM, I. A., MICHAIL, S. H. & ABD-EL-AZIZ, F. R., 1972 - Studies on the damping-off and root rot of soybean in Egypt - Phytopath. Medit. 11: 202-204.

242. EL-HISSY, F. T., 1974 - Fresh water fungi in Egypt. - Egypt. J. Bot. 17: 187-189.

243. ELLIOTT, C., 1942 - Relative susceptibility to Pythium root rot of twelve dent corn inbreds. - J. agric. Res. 64: 711-723.

244. ELLIOTT, C., 1943 - A Pythium stalk-rot of corn. - J. agric. Res. 66: 21-39.

245. ELLIOTT, C., MELCHERS, L. E., LEFEBVRE, C. L., & WAGNER, F. A., 1937 - Pythium root rot of milo. - J. agric. Res. 54: 797-834.

246. ELLIS, D. E. & COX, R. S., 1951 - The etiology and control of lettuce damping-off. - Tech. Bull. N. Carol. agric. Exp. Stn 94: l-33.

247. EL-REHIM, M., ABD, A., IBRAHIM, I. A., MICHAIL, S. H. & EL-MELEIGI, M. A., 1974 relationships between Pythium irregulare and certain tomato cultivars. - Zentbl. Bakt. ParasitKde, Abt 2, 129: 179-182.

248. EMERSON, R., 1958 - Mycological organization. - Mycologia 50: 589-621.

249. ENDO, R. M., 1963 - Influence of temperature on rate of growth of five fungus pathogens of turfgrass and on rates of disease spread. - Phytopathology 53: 857-861.

250. ERISTAVI, E. M. & MORDVINTZEFF, A. T., 1930 - A brief survey of plant diseases in Abkhasia in 1929. - Ivz. abkhaz. sel.-khoz. opyt. Sta. 41: 20 pp.

251. ERWIN, D. C & CAMERON, J. W., 1957 - Susceptibility of five sweet corn varieties to Pythium graminicola. - Pl. Dis. Reptr 41: 988-991.

252. ESCOBAR, C., BEUTE, M. K. & LOCKWOOD, J. L., 1967 - Possible importance of Pythium in root rot of peas. - Phytopathology 57: 1149-1151.

253. EZEKIEL, W. N., 1938 - Plant pathology and physiology. - Rep. Tex. agric. Exp. Stn 1937: 95-121.

254. FAJOLA, A. O. & ALASOADURA, S. O., 1974 - Studies on the damping-off disease of tobacco (Nicotiana tabacum) in Nigeria. - Mycopath. Mycol. appl. 52: 239-249.

255. FAJOLA, A. O. & ALASOADURA, S. O., 1975 - Antagonistic effects of Trichoderma harzianum on Pythium aphanidermatum causing the damping-off disease of tobacco in Nigeria. - Mycologia 57: 47-52.

256. FASSATIOVA, O., 1966 - Bodenmikromyceten am Hgel Doutnč im Bhmischen Karst. - Preslia 38: 1-14.

257. FATEMI, J., 1972a - Phytophthora and Pythium root rot of sugar beet in Iran. - Phytopath. Z. 71: 25-28.

258. FATEMI, J., 1972b - Pythiaceous fungi associated with citrus decline in Iran. - Phytopath. Z. 74: 153-160.

259. FATEMI, J., 1974 - A simple technique for isolation of Phytophthora and Pythium species from soil. - Phytopath. medit. 13: 120-121.

260. FELL, J. W. & MASTER, I. M., 1975 - Phycomycetes (Phytophthora spp. nov. and Pythium sp. nov.) associated with degrading mangrove (Rhizophora mangle) leaves. - Can. J. Bot 53: 2908-2922.

261. FERGUS, C. L., SINDEN, J. W., SCHIBLER, L. C. & SIGEL, E. M., 1963 - Possible detrimental effects of Pythium artotrogus on the cultivated mushroom. - Phytopathology 53: 1360-1362.

262. FILANI, C. A., 1975 - The occurrence and prevention of root and stem rot of coffee seedlings in Nigeria. - Pl. Dis. Reptr 59: 137-139.

263. FILER, T. H. JR., 1967 - Damping-off of sweet gum by Pythium sylvaticum. - Phytopathology 57: 1284.

264. FIRMAN, I. D., 1972 - A list of fungi and plant parasitic bacteria, viruses and nematodes in Fiji. - Phytopath. Pap. Commonw. mycol. Inst. 15: 36 pp.

265. FIRMAN, I. D., 1975 - Phytophthora and Pythium species and the diseases caused by them in the area of the South Pacific Commission. - Fiji agric. J. 37: 1-8.

266. FISCHER, A., 1892 - Phycomycetes. - Rabenhorst, Kryptogamenflora 1(4): 505 pp.

267. FISCHER, G. W., SPRAGUE, R, JOHNSON, H. W. & HARDISON, J. R, 1942 - Host and pathogen indices to the diseases observed on grasses in certain Western States during 1941. - Pl. Dis. Reptr, Suppl. 137: 87-144.

268. FISCHER, R., 1931 - Zur Bekmpfung des Wurzelbrandes der Zuckerrbe. - Nachr. SchdlBekmpf, Flrsheim 6: 33-35.

269. FITT, B. D. L. & HORNBY, D., 1978 - Effects of root infecting fungi on wheat transport processes and growth. - Physiol. Pl. Path. 13: 335-346.

270. FITZPATRICK, H. M., 1923 - Generic concepts in the Pythiaceae and Blastocladiaceae. - Mycologia 15: 166-173.

271. FLOR, H. H., 1930a - Factors infuencing the severity of root rot troubles of sugarcane. - Bull. Agric. Exp. Stn La St. Univ. 212: 40 pp.

272. FLOR, H. H., 1930b - Relation of environmental factors to growth and pathogenicity of Pythium isolated from roots of sugar cane. - Phytopathology 20: 319-328.

273. FLOWERS, R. A. & HENDRIX, J. W., 1969 - Gallic acid in a procedure for isolation of Phytophthora parasitica var. nicotianae and Pythium spp. from soil. - Phytopathology 59: 725-731.

274. FLOWERS, R.A. & LITTRELL, R. H., 1972 - Oospore germination of Pythium aphanidermatum as affected by casein, gallic acid, and pH levels in a selective agar medium. - Phytopathology 62: 757 (Abs.).

275. FOX, E., 1931 - Une maladie des pinards. l. Etude gnrale. - Revue Path. vg. Ent. agric. 18: 54-65.

276. FOWLKS, E. R, LEBEN, C. & SNELL, J. F., 1967 - Sterols in relation to the influence of nystatin on Pythium aphanidermatum and Colletotrichum lagenarium. - Phytopathology 57: 246-249.

277. FOX, N. C. & WOLF, F. T., 1977 - Aquatic phycomycetes of Radnor Lake, Nashville, Tennessee. - J. Tenn. Acad. Sci. 52: 100-104.

278. FRANK, Z. R., 1968 - Pythium root-rot of peanuts. - Phytopathology 58: 542-545.

279. FRANK, Z. R., 1971a - A rot of groundnut pods and the role of Pythium spp. in its etiology. - Diss. Hebrew Univ. Jerusalem.

280. FRANK, Z. R., 1971b - Forecasting peanut pod-rot potential by baiting Pythium from soil. - Isr. J. agric. Res. 21: 83-87.

281. FRANK, Z. R., 1972a - Groundnut pod-rot potential in three crop rotations as indicated by the relative Pythium population. - Pl. Soil 36: 89-92.

282. FRANK, Z. R., 1972b - Pythium myriotylum and Fusarium solani as co-factors in a pod-rot complex of peanut. - Phytopathology 62: 1331-1334.

283. FRANK, Z. R., 1972c - Notes on soil management in relation to Pythium rot of peanut pods. - Pl. Dis. Reptr 56: 600-601.

284. FRANK, Z. R. & ASHRI, A., 1977 - Breeding peanuts for resistance to Pythium myriotylum induced pod rot. - Phytoparasitica 5: 67-68.

285. FREEMAN, T. E., 1958 - Diseases of turf grasses. - Rep. Fla agric. Exp. Stn 1958: 142-143.

286. FREEMAN, T. E., 1960 - Cottony blight of ryegrass (Lolium sp.) caused by Pythium aphanidermatum. - A. Rep. Fla agric. Exp. Stn 1959: 143-144.

287. FREEMAN, T. E., 1963 - Age of ryegrass in relation to damage by Pythium aphanidermatum. - Pl. Dis. Reptr 47: 844.

288. FREEMAN, T. E., 1972 - Seed treatment for control of Pythium blight of ryegrass. - Pl. Dis. Reptr 56: 1043-1045.

289. FREEMAN, T. E. & HORN, G. C., 1963 - Reaction of turfgrasses to attack by Pythium aphanidermatum. - Pl. Dis. Reptr 47: 425-427.

290. FREEMAN, T. E., LUKE, H. H. & SECHLERS, D. J., 1966 - Pathogenicity of Pythium aphanidermatum on grain crops in Florida. - Pl. Dis. Reptr 50: 292-294.

291. FREZZI, M. J., 1956 - Especies de Pythium fitopatgenas identificadas en la Repblica Argentina. - Revta Invest. agric., B. Aires 10: 113-241.

292. FUJITA, Y., 1978 - Studies on pathogenic Pythium of laver red rot in Ariake Sea farm. 5. Germination of Pythium porphyrae oospores. - Bull. Jap. Soc. scient. Fish. 44: 15-20.

293. FUJITA, Y. & ZENITANI, B., 1977a - Studies on pathogenic Pythium of laver red rot in Ariake Sea farm. 2. Experimental conditions and nutritional requirements for growth. - Bull. Jap. Soc. scient. Fish. 43: 89-95.

294. FUJITA, Y. & ZENITANI, B., 1977b - Studies on pathogenic Pythium of laver red rot in Ariake Sea farm. 4. Serological differentiation of pathogenic Pythium strains. - Bull. Jap. Soc. scient. Fish. 43: 1313-1318.

295. FULLER, M. S., 1977 - The zoospore, hallmark of the aquatic fungi. - Mycologia 69:1-20.

295a FULLER, M. S., LEWIS, B. & COOK, P., 1966 -Occurrence of Pythium sp. on the marine alga Porphyra. - Mycologia 58: 313-318.

296. GALAAEN, R. & VENN, K., 1979 - Pythium sylvaticum and other fungi associated with root die-black of 2-0 seedlings of Picea abies in Norway. - Meddr Norsk Inst. Skogforsk. 34: 265-280.

297. GALLOWAY, L. D., 1935 - India: new plant diseases recorded in 1934. - Intern. Bull. Pl. Prot. 9: 176-178, 268.

298. GARBOWSKA, J. & JURASZKWNA, H., 1933 - Chorby rslin zytkowich w okresie 1926-30. - Roczn. Ochr. Rosl. A, 1: 97-235.

299. GARCA, R. & MITCHELL, D. J., 1975a - Synergistic interactions of Pythium myriotylum with Fusarium solani and Meloidogyne arenaria in pod rot of peanut. - Phytopathology 65: 832-833.

300. GARCA, R. & MITCHELL, D. J., 1975b - Interactions of Pythium myriotylum with Fusarium solani, Rhizoctonia solani and Meloidogyne arenaria in pre-emergence damping-off of peanut. - Pl. Dis. Reptr 59: 665-669.

301. GARCA, R. & MITCHELL, D. J., 1975c - Interaction of Pythium myriotylum with several fungi in peanut pod rot. - Phytopathology 65: 1375-1381.

302. GARREN, K. H., 1966 - Peanut microflora and pathogenesis in peanut pod rot. - Phytopath. Z. 55: 359-367.

303. GARREN, K. H., 1967 - Relation of several pathogenic organisms and the competition of Trichoderma viride to peanut pod breakdown. - Pl. Dis. Reptr 51: 601-605.

304. GARREN, K. H., 1970 - Rhizoctonia solani versus Pythium myriotylum as pathogens of peanut pod breakdown. - Pl. Dis. Reptr 54: 840-843.

305. GARREN, K. H., 1971 - Persistence of Pythium myriotylum in soils. - Phytopathology 61: 596-597.

306. GARREN, K. H. & PORTER, D. M., 1972 - Organic matter major elements and peanut breakdown. - Phytopathology 62: 759 (Abs.).

307. GARREN, K. H. & PORTER, D. M., 1975 - Peanut pod breakdown and peanut wilt. - Bull. U. S. Dep. Agric. S. Coop. Ser. (1974) 183: 61-64.

308. GARREN, K. H., PORTER, D. M. & GRIFFIN, G. J., 1974 - Rye green manure and the ecology of Pythium myriotylum. - Proc. Am. phytopath. Soc. 1: 29.

309. GARRETT, S. D., 1934 - Factors affecting the pathogenicity of cereal root-rot fungi. - Biol. Rev. 9: 351-361.

310. GATES, L. F. & HULL, R., 1954 - Experiments on black leg disease of sugar-beet seedlings. - Ann. appl. Biol. 41: 541-561.

311. GATTANI, M. L. & KAUL, T. N., 1951 - Damping-off of tomato seedlings - its cause and control. - Indian Phytopath. 4: 156-161.

312. GAY, J. D., 1969 - Effects of temperature and moisture on snap bean damping off caused by three isolates of Pythium myriotylum. - Pl. Dis. Reptr 53: 707-709.

313. GAY, J. D. & MCCARTER, S. M., 1968 - Stem rot of snap bean in southern Georgia caused by Pythium myriotylum. - Pl. Dis. Reptr 52: 416.

314. GEMAROAT, P. D. & PRASAD, N., 1965 - Pre-emergence blight of Sesamum caused by Pythium aphanidermatum. - Sci. Cult. 31: 315-316.

315. GILL, D. L., 1936 - Geranium cutting rots and their control. - Florists Exch. 87: 17.

316. GINDRAT, D., 1976 - Components in unbleached commercial chitin stimulate Pythium ultimum in sugar beet spermosphere. - Phytopathology 66: 312-316.

317. GIRGINKOC, H. R., 1951 - Untersuchungen ber die Zwarte Houtvatenziekte der Futterund Zuckerrbe, verursacht durch Pythium irregulare. - Meded. LandbHogesch. Wageningen 129: 1-61.

318. GOBI, C., 1899-1900 - Entwicklungsgeschichte des Pythium tenue n. sp. - Bot. Oboz. 15: 211-226.

319. GOIDNICH, G., 1939 - Le pi importanti malattie del sorgo, con speciale riferimento a quelle del sorgo zuccherino. - Industria saccar. ital. 32: 77-102, 166-168.

320. GOLDEN, J. K., POWELL, W. M. & HENDRIX, F. F. JR., 1972 - The influence of storage temperature on recovery of Pythium spp. and Meloidogyne incognita from field soils. - Phytopathology 62: 819-822.

321. GOLDIE-SMITH, E. K., 1952 - The sporangial phase of Pythium undulatum. - J. Elisha Mitchell scient. Soc. 68: 273-292.

322. GMEZ-MIRANDA, B. & LEAL, J. A., 1965 - Influencia del esterol, luz y fuente de nitrgeno en la reproduccin asexual de Phytophthora y Pythium. - Microbiol. espa.18: 235-245.

323. GOOT, P. VAN DER, 1935 - Ziekten en plagen der cultuurgewassen in Nederlandsch-Indi in 1934. - Meded. Inst. Plziekt. Buitenz. 85: 1-94.

324. GOOT, P. VAN DER, 1937 - Ziekten en plagen der cultuurgewassen in Nederlandsch-Indi in 1936. - Meded. Inst. Plziekt. Buitenz. 89:1-104.

325. GOTH, R. W., DE VAY, J. E. & SCHICK, F. J., 1967 - A quantitative method for the isolation of Pythium species from soil using sweet corn. - Phytopathology 57: 813 (Abs.).

326. GOTTLIEB, D., KNAUS, R. J. & WOOD, S. G., 1978 - Differences in the sterol synthesizing pathways of sterol-producing and non-sterol-producing fungi. - Phytopathology 68: 1168-1169.

327. GOTTLIEB, M. & BUTLER, K. D., 1939 - A Pythium root rot of cucurbits. - Phytopathology 29: 624-628.

328. GRAHAM, V. E. & GREENBERG, L., 1939 - The effect of salicylic aldehyde on the infection of wheat by Pythium arrhenomanes, and the destruction of the aldehyde by Actinomyces erythropolis and Penicillium sp. - Can. J. Res., Sect. C, 17: 52-56.

329. GRAVATT, A.R., 1925 - Direct inoculation of coniferous stems with damping-off fungi. - J. agric. Res. 30: 327-339.

330. GREGORY, K. F., ALLEN, O.N., RIKER, A.J. & PETERSON, W. H., 1952 - Antibiotics and antagonistic microorganisms as control agents against damping-off of alfalfa. - Phytopathology 42: 613-622.

331. GROUET, D., 1961 - Le Pythium de la tulipe - biologie, traitements. - Phytiat.Phytopharm. 10: 71-76.

332. GROVE, S. N. & BRACKER, C. E., 1968 - Protoplasmic differentiation in growing hyphal tips. - Am. J. Bot. 55: 702 (Abs.).

333. GROVER, R K. & DUTT, S., 1973 - Morphological and pathological variability in Pythium aphanidermatum. - Indian Phytopath. 26: 237-244.

333a. HAAN, J. DE, 1902 - Bsartige Schimmelkrankheit des Pferdes (Hyphomycosis destruens equi). - Centbl. Bakt. ParasitKde, Abt. 1, Orig., 31: 758-763.

333b. HAAN, J. DE & HOOGKAMER, L. J., 1901 - Hyphomycosis destruens. - Veeartsenijk. Bl. v. Ned.-Indi 13: 350-474.

333c. HAAN, J. DE & HOOGKAMER, L. J., 1903 - Hyphomycosis destruens equi. - Arch. wiss. prakt. Tierheilk. 29: 395-410.

334. HADDEN, C. H., 1966 - Studies on actinomycetes in relation to Pythium root rot of sugarcane and corn. - Diss. Abstr. 26: 4162.

335. HALL, C. J. J. VAN, 1925 a - Ziekten en plagen der cultuurgewassen in Nederlandsch-Indi in 1924. - Meded. Inst. PlZiekt. Buitenz. 67: l-53.

336. HALL, C. J. J. VAN, 1925b - Ziekten en plagen der cultuurgewassen in Nederlandsch-Indi in 1925. - Meded. Inst. PlZiekt. Buitenz. 70: 1-5 1.

337. HALLOCK, D. L. & GARREN, K. H., 1968 - Pod breakdown, yield and grade of Virginia peanuts as affected by Ca, Mg and K sulfates. - Agron. J. 60: 253-257.

338. HALPIN, J. E., HANSON, E. W. & DICKSON, J. G., 1952 - Studies on the pathogenicity of seven species of Pythium on red clover seedlings. - Phytopathology 42: 245-249.

339. HALPIN, J. E., HANSON, E. W. & DICKSON, J. G., 1954 - Studies on the pathogenicity of seven species of Pythium on alfalfa, sweetclover and Ladino clover seedlings. - Phytopathology 44: 572-574.

340. HAMPTON, R O., 1955 - Comparative pathogenicity of pythiaceous fungi on corn. - Iowa St. Coll. J. Sci. 30: 295-299.

341. HAMPTON, R O., 1957 - Host specialization in Pythium graminicola and pathogenicity of P. graminicola to four host species in soil amended with nitrogen and phosphorus. - Iowa. St. Coll. J. Sci. 32: 184-185.

342. HAMPTON, R. O. & BUCHHOLTZ, W. F., 1959 - Seasonal occurrence of Pythium graminicola in roots of field-grown corn. - Iowa St. Coll. J. Sci. 33: 489-495.

343. HAMPTON, R. O. & BUCHHOLTZ, W. F., 1962 - Host specialization in Pythium graminicola. - Iowa St. Coll. J. Sci. 37: 43-66.

344. HANCOCK, J. G., 1972 - Root rot of cotton caused by Pythium splendens. - Pl. Dis. Reptr 56:973-975.

345. HANCOCK, J. G., 1977 - Factors affecting soil populations of Pythium ultimum in the San Joaquin Valley of California. - Hilgardia 45: 107-122.

346. HANSFORD, C. G., 1938 - Annotated host list of Uganda parasitic fungi and plant diseases (parts 1-5). - E. Afr. agric. J. 4: 235-240.

347. HARDER, R. & BELMESSER, E., 1957 - Notiz zur Frage des Vorkommens von Chytridineen and anderen Pilzen in tiefen Bodenschichten. - Arch. Mikrobiol. 26: 353-357.

348. HARTER, L. L. & WHITNEY, W. A., 1927a - A transit disease of snap beans caused by Pythium aphanidermatum. - J. agric. Res. 34: 443-447.

349. HARTER, L. L. & WHITNEY, W. A., 1927b - Mottle necrosis of sweet potatoes. - J. agric.Res. 34: 893-914.

350. HARTER, L. L. & ZAUMEYER, W. J., 1931 - Pythium butleri, the cause of bean wilt. - Phytopathology 21: 991-994.

351. HARTLEY, C., 1921 - Damping-off in forest nurseries. - Bull. U.S. Dep. Agric. 934: 1-99.

352. HARVEY, J. V., 1925 - A study of the water molds and Pythiums occurring in the soils of Chapel Hill. - J. Elisha Mitchell scient. Soc. 41: 151-164.

353. HARVEY, J. V., 1927 - A survey of water molds occurring in the soils of Wisconsin as studied during the summer of 1926. - Trans. Wis. Acad. Sci. Arts Lett. 23: 551-565.

354. HARVEY, J. V., 1944a - Fungi associated with the decline of citrus and avocado in California. - Pl. Dis. Reptr 28: 565-568.

355. HARVEY, J. V., 1944b - Fungi associated with the decline of avocado and citrus in California. - Pl. Dis. Reptr 28: 1028-1031.

356. HARVEY, J. V.,1945 - Fungi associated with decline of avocado and citrus in California. - Pl. Dis. Reptr 29: 110-113.

357. HASKETT, W. C. & MURPHY, H. C., 1953 - Relative susceptibility of barley varieties to Pythium graminicola. - Phytopathology 43: 474 (Abs.).

358. HASKINS, R H., 1965 - Sterols and temperature tolerance in the fungus Pythium. - Science, N.Y. 150: 1615-1616.

359. HASKINS, R H., TULLOCH, A. P. & MIRCETICH, R. G., 1964 - Steroids and the stimulation of sexual reproduction of a species of Pythium. - Can. J. Microbiol. 10: 187-195.

360. HAWARE, M. P. & JOSHI, L. K., 1974 - Studies on soft rot of ginger from Madhya Pradesh. - Indian Phytopath. 27: 158-161.

361. HEBERT, L. P., 1964 - Culture of sugarcane for sugar production in Louisiana. - Agric. Handb. U.S. Dep. Agric. 262: l-40.

362. HECK, A.F., 1934 - Some indications of a relation of soil fertility and plant nutrition to cane diseases in Hawaii. - J. Am. Soc. Agron. 26: 381-389.

363. HENDRIX, F. F. JR. & CAMPBELL, W. A., 1966 - Root rot organisms isolated from ornamental plants in Georgia. - Pl. Dis. Reptr 50: 393-395.

364. HENDRIX, F. F. JR. & CAMPBELL, W. A., 1968a - Pythiaceous fungi isolated from forest nursery soils and their pathogenicity to pine seedlings. - Forest Sci. 14: 292-297.

365. HENDRIX, F. F. JR. & CAMPBELL, W. A., 1968b - A new heterothallic Pythium from the United States and Canada. - Mycologia 60: 802-805.

366. HENDRIX, F. F. JR. & CAMPBELL, W. A., 1969a - A new species of Pythium with spiny oogonia. - Mycologia 61: 387-391.

367. HENDRIX, F. F. JR. & CAMPBELL, W. A., 1969b - Heterothallism in Pythium catenulatum. - Mycologia 61: 639-641.

368. HENDRIX, F. F. JR. & CAMPBELL, W. A., 1970- Distribution of Phytophthora and Pythium species in soils in the continental United States. - Can. J. Bot. 48: 377-384.

369. HENDRIX, F. F. JR. & CAMPBELL, W. A., 1971 - A new species of Pythium with spiny oogonia and large chlamydospores. - Mycologia 63: 978-982.

370. HENDRIX, F. F. JR. & CAMPBELL, W. A., 1974 - Taxonomy of Pythium sylvaticum and related species. - Mycologia 66: 1049-1052.

371. HENDRIX, F. F. JR., CAMPBELL, W. A. & CHIEN, C. Y., 1971 - Some Phycomycetes indigenous to soils of old growth forests. - Mycologia 63: 283-289.

372. HENDRIX, F. F. JR., CAMPBELL, W. A. & MONCRIEF, J. B., 1970 - Pythium species associated with golf turfgrasses in the south and southeast - Pl. Dis. Reptr 54: 419-421.

373. HENDRIX, F. F. JR. & PAPA, K. E., 1974 - Taxonomy and genetics of Pythium. - Proc. Am. phytopath. Soc. 1: 200-207.

374. HENDRIX, F. F. JR. & POWELL, W. M., 1968 - Nematode and Pythium species associated with feeder root necrosis of pecan trees in Georgia. - Pl. Dis. Reptr 52: 334-335.

375. HENDRIX, F. F. JR., POWELL, W. M. & OWEN, J. H., 1966 - Relation of root necrosis caused by Pythium species to peach tree decline. - Phytopathology 56: 1229-1232.

376. HENDRIX, F. F. JR., POWELL, W. M., OWEN, J. H. & CAMPBELL, W. A., 1965 Pathogens associated with diseased peach roots. - Phytopathology 55: 1061 (Abs.).

377. HENDRIX, J. W., 1964 - Sterol induction of reproduction and stimulation of growth of Pythium and Phytophthora. - Science, N.Y. 144: 1028-1029.

378. HENDRIX, J. W., 1965 - Influence of sterols on growth and reproduction of Pythium and Phytophthora spp. - Phytopathology 55: 790-797.

379. HENDRIX, J. W., 1966 - Inability of Pythium aphanidermatum and Phytophthora palmivora to incorporate acetate into digitonin-precipitable sterols. - Mycologia 58: 307-312.

380. HENDRIX, J. W., 1975a - Cholesterol uptake and metabolism by Pythium and Phytophthora species. - Mycologia 67: 663-666.

381. HENDRIX, J. W., 1975b - Differential uptake and metabolism of sitosterol and cholesterol by Achlya, Pythium and Phytophthora species. - Can. J. Microbiol. 21: 735-737.

382. HENDRIX, J. W., BENNET, R. D. & HEFTMAN, E., 1970 - Metabolism of cholesterol by Pythium periplocum. - Microbios 2: 11-15.

383. HENDRIX, J. W. & LAUDER, D. K., 1966 - Effect of polyene antibiotics on growth and sterol-induction of oospore formation by Pythium periplocum. - J. gen. Microbiol. 44: 115-120.

384. HESSE, R., 1874 - Pythium debaryanum, ein endophytischer Schmarotzer. - Diss. Univ. Halle, 76 pp.

385. HICKMAN, C. J., 1944a - Phycomycetes occurring in Great Britain. l. Pythium mamillatum. - Trans. Br. mycol. Soc. 27: 49-5 1.

386. HICKMAN, C. J., 1944b - Phycomycetes occurring in Great Britain. 2. Pythium anandrum. - Trans. Br. mycol. Soc. 27: 52-54.

387. HICKMAN, C. J., 1944c - Phycomycetes occurring in Great Britain. 3. Pythium aphanidermatum. - Trans. Br. mycol. Soc. 27: 63-67.

388. HILDEBRAND, A. A. & KOCH, L. W., 1952 - Observations on a root and stem rot of soybeans new to Ontario caused by Pythium ultimum. - Scient. Agric. 32: 574-580.

389. HILDEBRAND, E. M. & COOK, H. T., 1959 - Sweet potato diseases. - Fmrs Bull. U.S. Dep. Agric. 1059: 1-28.

390. HINE, R. B.,1962 - Effect of streptomycin and pimaricin on growth and respiration of Pythium spp. - Phytopathology 52: 736 (Abs.).

391. HINE, R. B. & LUNA, L.,1963 - A technique for isolating Pythium aphanidermatum from soil. - Phytopathology 53: 727-728.

392. HIRANE, S., 1960 - (Studies on Pythium snow blight of wheat and barley, with special reference to the taxonomy of the pathogens.) - Trans. mycol. Soc. Jap. 2: 82-87.

393. HO, W.-C., 1944 - Soil-inhabiting fungi attacking the roots of maize. - Res. Bull. Ia agric. Exp. Stn 332: 403-446.

394. HO, W.-C. & MELHUS, I. E., 1940 - Succession of soil-inhabiting fungi attacking the roots of maize. - Phytopathology 30: 10 (Abs.).

395. HO, W. C., MEREDITH, C. H. & MELHUS, I. E., 1941 - Pythium graminicola on barley. - Bull. Ia agric. Exp. Stn 287: 284-314.

396. HOCH, H. C. & ABAWI, G. S., 1979a - Mycoparasitism of oospores of Pythium ultimum by Fusarium merismoides. - Trans. Br. mycol. Soc. 71: 621-625.

397. HOCH, H. C. & ABAWI, G. S., 1979b - Biological control of Pythium rootrot of tablebeet with Corticium sp. - Phytopathology 69: 417-419.

398. HOCH, H. C., HAGEDORN, D. J. & PINNOW, D. L., 1975 - Role of Pythium spp. as incitants of bean root and hypocotyl rot in Wisconsin. - Pl. Dis. Reptr 59: 443-447.

399. HHNK, W., 1932 - A new parasitic Pythium. - Mycologia 24: 489-507.

400. HHNK, W., 1939 - Ein Beitrag zur Kenntnis der Phycomyceten des Brackwassers. Kieler Meeresforsch. 3: 335-361.

401. HHNK, W., 1953 - Studien zur Brack-und Seewassermykologie. 3. Oomycetes, 2. - Verff. Inst. Meeresforsch. Bremerh. 2: 52-108.

402. HHNK, W., 1956 - Mykologische Abwsserungsstudie. - Verff. Inst. Meeresforsch. Bremerh. 4: 67-110.

403. HHNK, W., 1962 - ber die Phycomyceten der Insel Madeira. - Verff. Inst. Meeresforsch. Bremerh. 8: 99-108.

404. HOITINK, H. A. J., HERR, L. J. & SCHMITTHENNER, A. F., 1976 - Survival of some plant pathogens during composting of hardwood tree bark. - Phytopathology 66: 1369-1376.

405. HOLDEMAN, Q. L., 1951 - Tobacco stem rot of transplants and barn rot caused by Pythium aphanidermatum. - Phytopathology 41: 17 (Abs.).

406. HOLDEMAN, Q. L. & BURKHOLDER, W. H., 1956 - The identity of barn rots of flue-cured tobacco in South Carolina. - Phytopathology 46: 69-72.

407. HOLLAND, A.H., KENDRICK, J. B. JR., LANGE, W.H. & MACGILLIVRAY, J. H., 1953 - Production of green lima beans for freezing. - Circ. Calif. agric. Ext. Serv. 430: 1-22.

408. HOOKER, A. L., 1953a - Severity of corn seedling disease in Iowa soils. - Proc. Iowa Acad. Sci. 60: 158-162.

409. HOOKER, A. L., 1953b - Relative pathogenicity of Pythium species attacking seedling corn. - Proc. Iowa Acad. Sci. 60: 163-166.

410. HOOKER, A. L., 1956 - Correlation of resistance to eight Pythium species in seedling corn. - Phytopathology 46: 175-176.

411. HOPKINS, J. C. F., 1939 - A descriptive list of plant diseases in Southern Rhodesia and their control. - Mem. Dep. Agric. Sth Rhod. 2: 1-51.

412. HOPKIN S, J. C. F., 1956 - Tobacco diseases with special reference to Africa. - Commonw. Mycol. Inst., Kew, 178 pp.

413. HOPPE, P. E., 1959 - Pythium species still living in muck soil air-dried six years. - Phytopathology 49: 830-831.

414. HOPPE, P. E., 1966 - Pythium species still viable after 12 years in air-dried muck soil. - Phytopathology 56: 1411.

415. HORNBY, A. J. W., 1933 - Report of the assistant director and agricultural chemist. - Rep. Dep. Agric. Nyasald 1932: 36-47.

416. HORSFALL, J. G. & KERTSZ, Z. I., 1933 - Abnormal enlargement of peas from plants affected with root rot. - Bull. N.Y. St. agric. Exp. Stn 621: l-20.

417. HOUTEN, J. G. TEN, 1939 - Kiemplantenziekten van coniferen. - Diss. Univ. Utrecht, 125 pp.

418. HOUTEN, J. G. TEN, 1954 - Enige resultaten van het werk van I.P.O.-onderzoeken. - Meded. Dir. Tuinb. 17: 78-93.

419. HOWARD, F. L., ROWELL, J. B. & KEIL, H. L., 1951 - Fungus diseases of turf grasses. - Bull. Rhode Isl. agric. Exp. Stn 308: 56 pp.

420. HOWARD, K. L. & JOHNSON, T. W. JR., 1969 - Aquatic fungi of Iceland: some filamentous eucarpic and holocarpic species. - Mycologia 61: 496-510.

421. HOWARD, R J., PRATT, R G. & WILLIAMS, P. H., 1978 - Pathogenicity to carrots of Pythium species from organic soils of North America. - Phytopathology 68: 1293-1296.

422. HOWARD, R J. & WILLIAMS, P. H., 1974 - Carrot diseases incited by Pythium spp. - Proc. Am. phytopath. Soc. 1: 27.

423. HOYMAN, W. G., 1945 - Pythium aphanidermatum on Arizona flax in the Salt River Valley. - Pl. Dis. Reptr 29: 569-570.

424. HSIEH, H.-J., 1978 - An annotated list of Pythium in Taiwan. - Bot. Bull. Acad. sin., Taipei 19: 199-205.

425. HSIEH, H.-J. & CHANG, H.-S., 1976 - Five species of Pythium, two species of Pythiogeton new for Taiwan and Pythium afertile. - Bot. Bull. Acad. sin., Taipei 17: 141-150.

426. HSU, D.-S. & HENDRIX, F. F. JR., 1972 - Influence of temperature on oospore formation of four heterothallic Pythium spp. - Mycologia 64: 447-451.

427. HSU, D.-S. & HENDRIX, F. F. JR., 1973 - Influence of Criconemoides quadricornis on pecan feeder root necrosis caused by Pythium irregulare and Fusarium solani at different temperatures. - Can. J. Bot. 51: 1421-1424.

428. HSU, D.-S. & LIU, Y. C., 1966 - Companion of Pythium spp. causing sugarcane root rot - Rep. Taiwan Sugar Exp. Stn 42: 41-46.

429. HSU, J. C.,1963 - Study on Pythium root rot of sugarcane. - Rep. Taiwan Sugar Exp. Stn 32: 143-151.

430. HSU, S. C., 1965a - The morphology and physiology of Pythium catenulatum causing sugarcane root rot. - Rep. Taiwan Sugar Exp. Sm 37: 89-104.

431. HSU, S. C., 1965b - A root rot of sugarcane caused by Pythium catenulatum in Taiwan. - Phytopathology 55: 705-706.

432. HUBALEK, Z., 1974a - Fungi associated with free-living birds in Czechoslovakia and Yugoslavia. - Acta Sci. nat. Brno 8(3): 1-62.

433. HUBALEK, Z., 1974b - The distribution patterns of fungi in free-living birds. - Acta Sci. nat. Brno 8(9): 1-5 1.

434. HUNTER, R E., 1975 - Water moulds of the river Great Ouse and its tributaries. - Trans. Br. mycol. Soc. 65: 101-108.

435. HRLIMANN, J. H., RAABE, R. D. & WILHELM, S., 1974 - The effect of Pythium arrhenomanes on corn at different soil temperatures. - Proc. Am. phytopath. Soc. 1: 28.

435a. HUTCHINS, D. R & JOHNSTON, K. G., 1972 - Phycomycosis in the horse. - Aust. vet. J. 48:269-278.

436. HUTCHINSON, S. A. & KAMEL, M., 1956 - The effect of earthworms on the dispersal of soil fungi. - J. Soil Sci. 7: 213-218.

437. ILAG, L. L., 1976 - The cottony leak disease in the Philippines. - Pl. Dis. Reptr 60: 12-13.

438. ILIEVA, E., 1973 - Tomato diseases caused by Pythium butleri. - Gradinarska lozar. Nauka 10: 77-82.

439. ITO, S., 1943 - A comparative study on the pathogenicity of some species of Saprolegniaceae and Pythium on rice seedlings. - Ann. phytopath. Soc. Japan 12: 109-115.

440. ITO, S. & TOKUNAGA, Y., 1933 - Studies on the rot-disease of rice seedlings caused by Pythium species. - J. Fac. Agric. Hokkaido imp. Univ. 32: 201-233.

441. ITO, S. & TOKUNAGA, Y., 1935 - Notae mycologiae Asiae orientalis. l. - Trans. Sapporo nat. Hist. Soc. 14: 11-33.

442. ITO, T., 1944 - Some aquatic species of Phycomycetes found in Kyoto. - J. Jap. Bot. 20: 51-60.

443. IWAYAMA, S., 1933 - On a new snow-rot disease of cereal plants caused by Pythium sp. - Pamphlet Agric. Exp. Stn Toyama-Ken, Japan, 20 pp.

444. JACKSON, A. D., 1938 - New blight resistant milo. Quick action by experiment station checks ravages of new soil-borne disease. - South Seedsman 1(2): 9, 12.

445. JAIN, A. C., 1950 - Root rot of grape-vines (Vitis vinifera) caused by Pythium debaryanum var. viticolum new var. - Nagpur agric. Coll. Mag. 25: 7-9.

446. JAIN, A. C., 1951 - Pythium leaf-rot of lettuce. - Sci. Cult. 17: 258.

447. JAIN, A. C., 1951-1952 - Control of Pythium fruit-rot of cucurbits in Madhya Pradesh. - Nagpur agric. Coll. Mag. 26: 4-5.

448. JACOB, J. C. S, 1960 - Vlas. Vlasbrand (Pythium megalacanthum). - Jversl. Inst. plziektenk. Onderz. 1959: 135.

449. JACOB. J. C. S, 1962 - Vlasbrand (Pythium megalacanthum). - Jversl. Inst. plziektenk. Onderz. 1961: 128.

450. JACOB, J. C. S, 1963 - Vlasbrand (Pythium megalacanthum). - Jversl. Inst. plziektenk. Onderz. 1962: 129.

451. JACOB, J. C. S, 1964 - Vlasbrand (Pythium megalacanthurn). - Jversl. Inst. plziektenk. Onderz. 1963: 112.

452. JANARDHANAN, K. K., GUPTA, M. L. & HUSAIN, A., 1977 - Pythium die-back, a new disease of Catharanthus roseus. - Indian Phytopath. 30: 427-428.

453. JANARDHANAN, K. K. & HUSAIN, A., 1974 - Production of a toxic metabolite and pectolytic enzyme by Pythium butleri. - Mycopath. Mycol. appl. 52: 305-330.

454. JANI, S. M. & PATEL, A. J., 1971a - Stem-rot of papaya (Carica papaya) and its control. - Abs. 2nd int. Symp. Pl. Path., Post-Symp. Disc. Group, New Delhi: 20.

455. JANI, S. M. & PATEL, A. J., 1971b - Stem-rot of papaya and its control. - Abs. 2nd int. Symp. Pl. Path., Post-Symp. Disc. Group, New Delhi: 26.

456. JENKINS, W. A., 1954 - Outbreak of Pythium rot in newly set flue-cured tobacco in Virginia. Pl. Dis. Reptr 38: 421.

457. JOCHEMS, S. C. J., 1926 - Handleiding voor herkenning en bestrijding van de ziekten van Deli-Tabak. - Meded. Deli-Proefstn Medan 2, 43: 1-39.

458. JOCHEMS, S. C. J., 1927 - Parasitaire stengelverbranding bij Deli-Tabak. - Meded. Deli Proefstn Medan 2, 49: 1-35.

459. JOHANN, H., HOLBERT, J. R & DICKSON, J. G., 1928 - A Pythium seedling blight and root rot of dent corn. - J. agric. Res. 37: 443-464.

460. JOHNSON, A. W. & LITTRELL, R. H., 1970 - Pathogenicity of Pythium aphanidermatum to Chrysanthemum in combined inoculations with Belonolaimus longicaudatus or Meloidogyne incognita. - J. Nematol. 2: 255-259.

461. JOHNSON, L. F., 1952a - The relation of antagonistic microorganisms to Pythium root rot of sugarcane and corn in recontaminated soils. - Proc. La Acad. Sci. 15: 24-31.

462. JOHNSON, L. F., 1952b - Control of root rot of corn under greenhouse conditions by microorganisms antagonistic to Pythium arrhenomanes. - Phytopathology 42: 468 (Abs.).

463. JOHNSON, L. F., 1954 - Antibiosis in relation to Pythium root rot of sugarcane and corn. - Phytopathology 44: 69-73.

464. JOHNSON, L. F., 1959 - Pythium root rot, an important disease of corn. - Prog. Rep. Tenn. Farm. Home Sci. 32: 4-5.

465. JOHNSON, L. F., 1979 - Susceptibility of cotton seedlings to Pythium ultimum and other pathogens. - Pt. Dis. Reptr 63: 59-62.

466. JOHNSON, L. F., BAIRD, D. D., CAMBERS., A. Y. & SHAMIYEH, N. B., 1978 - Fungi associated with post-emergence seedling disease of cotton in three soils. - Phytopathology 68: 917-920.

467. JOHNSON, L. F. & CHAMBERS, A. I., 1973 - Isolation and identity of three species of Pythium that cause cotton seedling blight. - PI. Dis. Reptr 57: 848-852.

468. JOHNSON, T. W. JR., 1968 - Aquatic fungi of Iceland. 1. Introduction and preliminary account - J. Elisha Mitchell scient. Soc. 84: 179-183.

469. JOHNSON, T. W. JR., 1971 - Aquatic fungi of Iceland: Pythium. - Mycologia 63: 517-536.

470. JOHNSON, T. W. JR., 1974 - Aquatic fungi of Iceland: Biflagellate species. - Acta nat islandica 23: 1-40.

471. JOHNSON, T. W. JR. & SPARROW, F. K., 1961 - Fungi in oceans and estuaries. - J. Cramer, Lehre.

472. JOHNSON, V., 1955 -New Geranium diseases in New South Wales. - Aust. Pl. Dis. Rec. 7: 54.

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475. JONES, D. L. & GAINES, F., 1938 - Report of substation no. 8, Lubbock. - A. Rep. Texas agric. Exp. Stn 1937: 229-235.

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483. KAZAMA, F. Y. & FULLER, M. S., 1970 - Ultrastructure of Porphyra perforata infected with Pythium marinum, a marine fungus. - Can. J. Bot. 48: 2103-2107.

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492. KESHWAL, R. L. & JOSHI, L. K., 1972 - Studies on certain soil fungi antagonistic to Pythium debaryanum. - Indian Phytopath. 25: 566-569.

493. KHESWALLA, K. F., 1936 - Fruit diseases in Baluchistan. - Agriculture Live-Stk India 6: 204-215.

494. KHULBE, R. D. & BHARGAVA, K. S., 1977 - Distribution and seasonal periodicity of water molds in some lakes in Nainital. - Hydrobiologica 54: 67-72.

495. KHULBE, R. D. & SATI, S. C., 1979 - Pythium undulatum, a new pathogen of Carassius auratus. - Geobios (Jodhpur) 6: 178.

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499. KIM, S. H., FORER, L. B. & LONGENECKER, J. L., 1975 - Recovery of plant pathogens from commercial peat products. - Proc. Am. phytopath. Soc. 2: 124.

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502. KLEMMER, H. W. & NAKANO, R. Y., 1964 - Distribution and pathogenicity of Phytophthora and Pythium in pineapple soils of Hawaii. - Pl. Dis. Reptr 48: 848-852.

503. KLIEJUNAS, J. T. & KO, W. H., 1975 - The occurrence of Pythium vexans in Hawaii and its relation to ohia decline. - Pl. Dis. Reptr 59: 392-395.

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505. KNAPHUS, G., 1964 - Fungistasis of Pythium graminicola in soil. - Diss. Abstr. 25: 2699.

506. KNAPHUS, G., 1967 - Inhibition of mycelial growth of Pythium graminicolum by soil fungi. - Proc. Iowa Acad. Sci. 72: 47-51.

507. KNAPHUS, G. & BUCHHOLTZ, W. F., 1958 - Vertical distribution of Pythium graminicola in soil. - Iowa St. Coll. J. Sci. 33: 201-207.

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509. KNAUSS, J. F., 1972b - Field evaluation of several soil fungicides for control of Scindapsus aureus cutting decay incited by Pythium splendens. - Pl. Dis. Reptr 56: 1074-1077.

510. KNAUSS, J. F., 1976 - In vitro antagonistic activity of several Streptomyces spp. against species of Pythium and Phytophthora. - Pl. Dis. Reptr 60: 846-850.

511. KNAUSS, J. F., 1978 - Control of Schefflera seedling decay with CGA-48988. - Pl. Dis. Reptr 62: 723-726.

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517. KOIKE, H., 1971 - Individual and combined effects of Pythium tardicrescens and Pythium graminicola on sugarcane: a first report. - Pl. Dis. Reptr 55: 766.

518. KOIKE, H. & YANG, S., 1971 - Influence of sugarcane mosaic virus strain H and Pythium graminicola on growth of sugarcane. - Phytopathology 61: 1090-1092.

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524. KRAFT, J. M., 1974 - The influence of seedling exudates on the resistance of peas to Fusarium and Pythium root rot. - Phytopathology 64: 190-193.

525. KRAFT, J. M. & BURKE, D. W., 1971 - Pythium ultimum as a root pathogen of beans and peas in Washington. - Pl. Dis. Reptr 55: 1056-1060.

526. KRAFT, J. M., ENDO, R M., & ERWIN, D. C.,1967 - Infection of primary roots of bentgrass by zoospores of Pythium aphanidermatum. - Phytopathology 57: 86-90.

527. KREUTZER, W. A. & DURRELL, L. W., 1938 - Rot of mature tap root of sugar beet caused by Pythium butleri. - Phytopathology 28: 512-515.

528. KRBER, H., 1979 - Auflaufschden bei einigen Kulturpflanzen nach Bodenverseuchung mit verschiedenen Pythium-Arten und Herknften. - Jber. biol. BundAnst. Land- u. Forstw. Braunschweig 1978: H 76.

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530. KRBER, H. & KIEWNICK, L., 1978 - Forschungen ber Arten der Gattungen Phytophthora und Pythium und von ihnen verursachte Pflanzenkrankheiten. - Jber. biol. BundAnst. Land- u. Forstw. Braunschweig 1977: H 74.

531. KRBER, H., 1977 - Pythium-Schwarzfule an Cattleyen. - Jber. biol. BundAnst. Land- u. Forstw. Braunschweig 1976: H 56.

532. KRBER, H. & PLATE, H.-P., 1976 - Eine bisher unbekannte Fule an Gerbera. - Jber. biol. BundAnst Land- u. Forstw. Braunschweig 1975: H 57.

533. KRBER, H. & STAHL, M., 1973 - Phytophthora- und Pythium-Schden an Gliederkakteen. - Jber. biol. BundAnst. Land- u. Forstw. Braunschweig 1972: P 44.

534. KRBER, H. & STAHL, M., 1974a - Erforschung von Phytophthora- und Pythium-Arten und von ihnen verursachte Planzenkrankheiten. - Jber. biol. BundAnst. Land- u. Forstw. Braunschweig 1973: P 61.

535. KRBER, H. & STAHL, M., 1974b - Wurzelfule an grtnerisch wichtigen Kakteen durch Pythium irregulare. - Phytopath. Z. 81: 38-48.

536. KRBER, H. & ZINKERNAGEL, V., 1978 - Pythium-Wurzelfule und Tracheomycose an Kopfsalat. - Jber. biol. BundAnst. Land- u. Forstw. Braunschweig 1977: H 73.

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538. KUSAKARI, S.-I. & UEYAMA, A., 1975 - Degradation of the mycelia of Pythium aphanidermatum by lytic actinomycetes in soil. - Trans. mycol. Soc. Japan 16: 55-62.

539. KUSAKARI, S.-I., TSUJI, H., YAMADA, K. & TANAKA, Y., 1979 - Damping-off of spinach seedlings caused by Pythium sp. - Ann. phytopath. Soc. Japan 45: 268-271.

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550. LIPPS, P. E. & BRUEHL, G. W., 1978 - Snow rot of winter wheat in Washington. - Phytopathology 68: 1120-1127.

550a. LIPPS, P. E. & BRUEHL, G. W., 1980 - Infectivity of Pythium spp. zoospores in snow rot of wheat - Phytopathology 70: 723-726.

551. LITTRELL, R H. & FLOWERS, R A., 1973 - Isolates of Rhizoctonia solani non-antagonistic and antagonistic to Pythium aphanidermatum. - Abs. 2nd int Cong. Pl. Path., Univ. Minnesota, Minneapolis: 1061.

552. LITTRELL, R H. & JOHNSON, A. W., 1969 - Pathogenicity of Pythium aphanidermatum to Chrysanthemum in combined inoculations with Belonolaimus longicaudatus or Meloidogyne incognita. - Phytopathology 59: 115-116 (Abs.).

553. LITTRELL, R H. & MCCARTER, S. M., 1970 - Effect of soil temperature on virulence of Pythium aphanidermatum and Pythium myriotylum to rye and tomato. - Phytopathology 60: 704-707.

554. LIU, L.-J., 1977 - Pathogenicity, biology, interaction with ratoon stunting causal agent, and in vitro sensitivity to herbicides to several Pythium isolates from sugarcane in Puerto Rico. - Proc. Am. phytopath. Soc. 4: 179.

555. LIU, L.-J. & SERAPION, J. L., 1977 - Etiology and control of root rot of Anthurium in Puerto Rico. - Proc. Am. phytopath. Soc. 4: 179.

556. LIU, P. S. W., 1977a - Diseases caused by Phytophthora and Pythium recorded in Sabah, Malaysia. - Tech. Bull. Dep. Agric., Sabah, Malay. 3: 48 pp.

557. LIU, P. S. W., 1977b - A supplement to a host list of plant diseases in Sabah, Malaysia. - Commonw. mycol. Inst. Kew, Phytopath. Pap. 21: 50 pp.

558. LJOGENJKAJA, E. I., 1966 - Species pro URSS nova Pythium irregulare. - Nov. Sist niz. Rast 1966: 141-142.

559. LOGVINENKO, L.I., 1970 - Phycomycetes of sewage of the Bezludovsk purifying constructions. - Mykrobiol. Zh. 32: 317-322.

560. LONG, P. G. & COOKE, R C., 1969 - Fungal factors and density-induced mortality in plant species. - Trans. Br. mycol. Soc. 52: 49-55.

561. LORIO, P. L. JR., 1966 - Phytophthora cinnamomi and Pythium species associated with loblolly pine decline in Louisiana. - Pl. Dis. Reptr 50: 596-597.

562. LUGAUSKAS, A. Y., MIKULSKENE, A. I. & BUBINENE, I. I., 1975 - Mycoflora of the rhizophere of red clover cultivated in various soils of Lithuanian SSR - Liet TSR Mokslu, Akad. biol. Inst. Darb., Ser. C, 2: 3-17.

563. LUKE, H. H. & CONNELL, T. D., 1954 - Studies on antibiotic soil organisms. 2. Bacteria and fungi antagonistic to Pythium arrhenomanes in sugarcane soils of Louisiana. - Phytopathology 44: 377-379.

564. LUMSDEN, R D. & AYERS, W. A., 1975 - Influence of soil environment on the germinability of constitutively dormant oospores of Pythium ultimum. - Phytopathology 65: 1101-1107.

565. LUMSDEN, R D. & AYERS, W. A., 1977 - Mycoparasitism of Pythium oospores by Fusarium spp. - Proc. Am. phytopath. Soc. 4: 217.

566. LUMSDEN, R D., AYERS, W. A., ADAMS, P. B., DOW, R L., LEWIS, J. A., PAPAVIZAS, G. C. & KANTZES, J. G., 1976 - Ecology and epidemiology of Pythium species in field soil. - Phytopathology 66: 1203-1209.

567. LUMSDEN, R D., AYERS, W. A. & DOW, R. L., 1975 - Differential isolation of Pythium species from soil by means of selective media, temperature and pH. - Can. J. Microbiol. 21: 606-612.

568. LUMSDEN, R. D. & HAASIS, F. A., 1964 - Pythium root and stem diseases of Chrysanthemum in North Carolina. - Tech. Bull. N. Carol. Agric. Exp. Stn 158: 1-27.

569. LUND, A., 1934 - Studies on Danish freshwater Phycomycetes and notes on their occurrence particularly relative to the hydrogen ion concentration of the water. - Skr. K. dansk. Vid. Selsk., naturv. math. Afd. 9: 1-97.

570. LUIJK, A. VAN, 1934a - Untersuchungen ber Krankheiten der Grser. - Meded. phytopath. Lab. Willie Commelin Scholten 13: 1-22.

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572. LUIJK, A. VAN, 1938a - Antagonism between various microorganisms and different species of the genus Pythium, parasitizing upon grasses and lucerne. - Meded. phytopath. Lab. Willie Commelin Scholten 14: 43-82.

573. LUIJK, A. VAN, 1938b - Antagonism of Penicillium sp. versus Pythium de Baryanum. - Chron. bot. 4: 210-211.

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576. MCCARTER, S. M. & LITTRELL, R. H., 1968 - Pathogenicity of Pythium myriotylum to several grass and vegetable crops. - Pl. Dis. Reptr 52: 179-183.

576a. MCCARTER, S. M. & LITTRELL, R. H., 1969 - Susceptibility of twelve crops to selected isolates of Pythium aphanidermatum and P. myriotylum. - Phytopathology 59: 116 (Abs.).

577. MCCARTER, S. M. & LITTRELL, R. H., 1970 - Comparative pathogenicity of Pythium aphanidermatum and P. myriotylum to 12 plant species and intraspecific variation in virulence. - Phytopathology 60: 264-268.

578. MCCOMBS, C. L. & WINSTEAD, N. N., 1963 - Control of cucumber cottony leak in transit. - Proc. Am. Soc. hort. Sci. 83: 538-546.

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580. MCKEEN, W. E., 1977 - Growth of Pythium graminicola in barley roots. - Can. J. Bot. 55: 44-47.

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587. MAHMUD, K. A., 1950a - Damping-off of cabbage, cauliflower and kohlrabi caused by Pythium aphanidermatum. - Curr. Sci. 19: 67-68.

588. MAHMUD, K. A., 1950b - Root rot of radish caused by Pythium aphanidermatum. - Allahabad Fmr 24(2): l-2.

589. MAHMUD, K. A., 1952a - Damping-off of Brassica juncea caused by Pythium aphanidermatum. - Sci. Cult. 17: 208-209.

590. MAHMUD, K. A., 1952b - Root rot of maize caused by Pythium aphanidermatum. - Sci. Cult. 17: 339.

591. MAHMUD, K. A., 1952c - Pythium damping-off of brinjal seedlings. -Sci. Cult. 18: 149-150.

592. MAHMUD, K. A. & JAIN, A. C., 1951 - Damping-off of Ipomoea pulchella due to Pythium aphanidermatum. - Sci. Cult. 16: 562.

593. MALAGUTI, G. B., 1963 - Outbreaks and new records. Plant disease situation in Venezuela during 1962. - Pl. Prot. Bull. F.A.O. 11: 43-45.

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622. MELCHERS, L. E.,1940 - The reaction of sorghum varieties and hybrids to milo disease. - Pl. Dis. Reptr, Suppl. 126: 165-175.

623. MELCHERS, L. E. & LOWE, A. E., 1943 - The development of sorghums resistant to milo disease. - Tech. Bull. Kansas agric. Exp. Stn 55: 1-24.

624. MELENDZ, P. L. & POWELL, N. T., 1969 - The influence of Meloidogyne on root decay in tobacco caused by Pythium and Trichoderma. - Phytopathology 59: 1348 (Abs.).

625. MELENDZ, P. L. & POWELL, N. T., 1970 - The Pythium root-knot nematode complex in flue-cured tobacco. - Phytopathology 60: 1303 (Abs.).

626. MELHUS, I. E., 1938 - Botany and plant pathology section. - Rep. Iowa agric. Exp. Stn 1938(1): 103-121.

627. MELHUS, I. E., 1940 - Pathology and mycology of cour. - Rep. Iowa agric. Exp. Stn 1939-40(2): 48-54.

628. MELHUS, I. E., MARTIN, J. N., REDDY, C. S., BUCHHOLTZ, W. F. &MURPHY, H. C., 1940 - Influence of Pythiaceous and other fungi on seedling stands of legumes and other crops. - Rep. Iowa agric. Exp. Stn 1940(l): 132-151.

629. MELHUS, I. E., REDDY, C. S. & BUCHHOLTZ, W. F., 1939 - Influence of pythiaceous and other fungi on seedling stands of legumes and other crops. - Rep. Iowa agric. Exp. Stn 1938(1): 114-115.

630. MELLANO, H. M., MUNNECKE, D. E. & ENDO, R. M., 1970 - Relationship of seedling age to development of Pythium ultimum on roots of Antirrhinum majus. - Phytopathology 60: 935-942.

631. MELLANO, H. M., MUNNECKE, D. E. & SIMS, J. J., 1970 - Relationship of pectic enzyme activity and presence of sterols to pathogenicity of Pythium ultimum on roots of Antirrhinum majus. - Phytopathology 60: 943-950.

632. MEREDITH, C. H., 1938 - Phycomycetes in Iowa soil. - Phytopathology 28: 15-16 (Abs.).

633. MEREDITH, C. H., 1940 - A quick method of isolating certain phycomycetous fungi from the soil. - Phytopathology 30: 1055-1056.

634. MESHCHERYAKOVA, R L., 1970 - (Pythium fungi from purifying constructions.) - Mykrobiol. Zh. 32: 210-215.

635. MESHCHERYAKOVA, R I. & LOGVINENKO, L. I., 1970 - (Species composition of the genus Pythium in water basins of the Ukrainian S. S. R.) - Mikol. Fitopatol. 4: 541-543.

636. MEURS, A., 1928 - Wortelrot, veroorzaakt door schimmels uit de geslachten Pythium en Aphanomyces. - Diss. Univ. Utrecht, 94 pp.

637. MEURS, A., 1929 - Ein neuer Wurzelbranderreger der Zucker- and Futterrben. - Phytopath. Z. 1: 111-126.

638. MEURS, A., 1934 - Parasitic stembuur of Deli tobacco. - Phytopath. Z. 7: 169-185.

639. MIDDLETON, J. T., 1938 - Plant diseases caused by Pythium spp. observed in California in 1938. - Pl. Dis. Reptr 22: 354-356.

640. MIDDLETON, J. T., 1941a - Some diseases of belladonna in California and their control. - Pl. Dis. Reptr 25: 513-514.

641. MIDDLETON, J. T., 1941b - Root rot of barley caused by Pythium hypogynum n. sp. - Phytopathology 31: 863 (Abs.).

642. MIDDLETON, J. T., 1942a - Stem rot of tuberous begonia. - Bull. Torrey bot. Club 69: 92-99.

643. MIDDLETON, J. T., 1943 - The taxonomy, host range and geographic distribution of the genus Pythium. - Mem. Torrey bot. Club 20: 1-171.

644. MIDDLETON, J. T., 1947a - Pythium crown rot of rhubarb. - Bull. Torrey bot. Club 74: 1-8.

645. MIDDLETON, J. T., 1947b - Root rot of condiment sage. - Phytopathology 37: 363 (Abs.).

646. MIDDLETON, J. T., 1950a - The synonymy of Pythium dissotocum and Pythium perigynosum. - Mycologia 42: 563-565.

647. MIDDLETON, J. T., 1950b - Pythium root rot of leguminosae. - Proc. int. bot. Cong. Stockholm 7: 724-725.

648. MIDDLETON, J. T., 1952 - Pythium seed decay and seedling blight of Pisum sativum. - Phytopathology 42: 516 (Abs.).

649. MIDDLETON, J. T., STONE, M. W. & KENDRICK, J. B. JR., 1949 - Incidence of lima bean root rot in soils treated with fumigants and insecticides for control of wireworms. - Phytopathology 39: 813-821.

650. MIDDLETON, J. T., TUCKER, C. M. & TOMPKINS, C. M., 1942 - Pythium disease of fibrous-rooted Begonia and its control. - J. agric. Res. 65: 89-95.

651. MIDDLETON, J. T. & WHITAKER, T. W., 1946 - Some diseases of cantaloups and honeydew melons observed in southern California. - Pl. Dis. Reptr 30: 373-375.

652. MIESTINGER, K., FISCHER, R., WATZL, O. & PORSCH, L., 1932 - Wichtige Schdlinge and Krankheiten der Rube in sterrreich - Bauernschr. N. st. Landes-Landw. Kammer 37: l-28.

653. MILANEZ, A. I., 1978 - Pythium echinulatum from Michigan soils. - Nova Hedwigia 29: 557-563.

654. MILDENHALL, J. P., PRATT, R. G., WILLIAMS, P. H. &MITCHELL, J. E., 1971 - Pythium brown root and forking of muck-grown carrots. - Pl. Dis. Reptr 55: 536-540.

655. MILLER, C. M., 1965 - Annotated list of aquatic Phycomycetes from Mountain Lake Biological Station, Virginia. - Virginia J. Sci., N.S. 16: 219-228.

656. MILLER, C. R., 1966 - Observations on the mode of infection and anatomical effects of Pythium ultimum and Phytophthora cactorum on young roots of Prunus persica. - Diss. Abstr. 26: 6956.

657. MILLER, C. R., DOWLER, W. M., PETERSON, D. H. & ASHWORTH, R. P., 1966 - Observations on the mode of infection of Pythium ultimum and Phytophthora cactorum on young root of peach. - Phytopathology 56: 46-49.

658. MILLER, J. H., GIDDENS, J. E. & FOSTER, A. A., 1957 - A survey of the fungi of forests and cultivated soils of Georgia. - Mycologia 49: 779-808.

659. MILLER, P. R, 1954 - Plant disease situation in the United States. - Pl. Prot. Bull. F.A.O. 3: 24-26.

660. MILSUM, J. N. & GRIST, D. H., 1941 - Vegetable gardening in Malaya. - Agric. Dept S.S. and F.M.S., Kuala Lumpur. 206 pp.

661. MINDEN, M. VON, 1902 - ber Saprolegniineen. - Centbl. Bakt. ParasitKde, Abt. 2, 8: 805-810.

662. MINDEN, M. VON, 1916 - Beitrge zur Biologie and Systematik einheimischer submerser Phycomyceten. - Mykol. Unters. Ber. 1: 146-255.

663. MIRCETICH, S. M., 1971 - The role of Pythium in feederroots of diseased and symptomless peach trees and in orchard soils in peach tree decline. - Phytopathology 61: 357-360.

664. MIRCETICH, S. M. & FOGLE, H. W., 1969 - Role of Pythium in damping-off of peach. - Phytopathology 59: 356-358.

665. MIRCETICH, S. M. & KEIL, H. L., 1970 - Phytophthora cinnamoni root rot and stem canker of peach trees. - Phytopathology 60: 1376-1382.

666. MIRCETICH, S. M. & KRAFT, J. M., 1973 - Efficiency of various selective media in determining Pythium population in soil. - Mycopath. Mycol. appl. 50: 151-161.

667. MITCHELL, D. J., 1975 - Density of Pythium myriotylum oospores in soil in relation to infection of rye. - Phytopathology 65: 570-575.

668. MITCHELL, R. & HURWITZ, E., 1965 - Suppression of Pythium debaryanum by lytic rhizosphere bacteria. - Phytopathology 55: 156-158.

669. MITCHELL, R. & W IBSEN, C., 1968 - Lysis of non-marine fungi by marine microorganisms. - J. gen. Microbiol. 52: 335-342.

670. MITRA, M., 1925 - Report of the imperial mycologist. - Scient. Rep. Agric. Res. Inst. Pusa 1924-25:45-57.

671. MITRA, M., 1927 - Fruit rot diseases of cultivated Cucurbitaceae caused by Pythium aphanidermatum. - Proc. 14th Indian Sci. Congr. Lahore, Bot. 5: 213-214.

672. MITRA, M. & SUBRAMANIAM, L. S., 1928 - Fruit-rot diseases of cultivated Cucurbitaceae caused by Pythium aphanidermatum. - Mem. Dep. Agric. India, Bot. 15: 79-84.

673. MOESZ, G., 1938 - Fungi Hungariae 2. Archimycetes et Phycomycetes. - Annls. Hist.-nat. Mus. Hung. 31: 58-109.

674. MONTAGNE, C., 1845 - Editorial. - Grdrs Chron. 38: 640.

675. MONTAGNE, C., 1848 - II. Observations, botanical and physiological, on the potato murrain. - Jl. R Hort. Soc. 1: 9-34.

676. MONTEITH, J., 1933 - A Pythium disease of turf. - Phytopathology 23: 23-24 (Abs.).

677. MONTGOMERY, N., 1954 - Damping-off of tomato by species of Pythium and its control by use of formalin dust. - J. Hort. Sci. 29: 245-257.

678. MOREAU, C. & MOREAU, M., 1958 - Le blast des jeunes palmiers huile. Observations sur le systme radiculaire de lhte et sur ses parasites. - Revue Mycol. 23: 201-232.

679. MORGAN, F. L. & HARTWIG, E. E., 1964 - Pythium aphanidermatum, a virulent soybean pathogen. - Phytopathology 54: 901 (Abs.).

680. MOORE, L. D. & COUCH, H. B., 1961 - Pythium ultimum and Helminthosporium vagans as foliar pathogens of Gramineae. - Pl. Dis. Reptr 45: 616-619.

681. MOORE, W. C., 1940a - New and interesting plant diseases. - Trans. Br. mycol. Soc. 24: 59-63.

682. MOORE, W. C., 1940b - New and interesting plant diseases. - Trans. Br. mycol. Soc. 24: 345-351.

683. MOORE, W. C. & BUDDIN, W., 1937 - A new disease of tulip caused by species of Pythium. - Ann. appl. Biol. 24: 752-761.

684. MULDER, D., 1969 - The pathogenicity of several Pythium species to rootlets of apple seedlings. - Neth. J. Pl. Path. 75: 178-181.

685. MULLER, H. R A. & VAN EEK, T., 1939 - Aanteekeningen over eenige ziekten van roselle en Java jute op Java. - Meded. alg. Proefstn Landb. Batavia 32: 1-21.

686. MUMFORD, F. B., 1930 - Progress in agricultural research. - Bull. Mo. agric. Exp. Stn 300: 1-107.

687. MUMFORD, F. B. & SHIRKY, S. B., 1937 - Science points the way. Work of the Agricultural Experiment Station during the year ending June 30, 1936. - Bull. Mo. agric. Exp. Stn 387: 1-121.

688. MUNNECKE, D. E. & MOORE, B. J., 1969 - Effects of storage at -18 C of soil infested with Pythium or Fusarium on damping-off of seedlings. - Phytopathology 59: 1517-1520.

689. MUNNECKE, D. E., MOORE, B. J. & EL-HAJ, F., 1971 - Soil moisture effects on control of Pythium ultimum or Rhizoctonia solani with methyl bromide. - Phytopathology 61: 194-197.

690. MURPHEY, H. C., 1947 - A study of the parasitism of the rusts, smuts and other diseases affecting oats. - Rep. Iowa agric. Exp. Stn 1947: 156-158.

691. MUSE, R. R., SCHMITTHENNER, A. F. & PARTYKA, R. E., 1974 - Pythium spp. Associated with foliar blighting of creeping bentgrass. - Phytopathology 64: 252-253.

692. MUTHUSAMY, M., RAJAGOPALAN, C. K. S. & VIDHYASEKARAN, P., 1973 - Role of pectic and cellulolytic enzymes in pathogenesis of Pythium aphanidermatum in tomato seedlings. - Madras agric. J. 60: 539-542.

693. MUTHUSAMY, M., VIDHYASEKARAN, P. & RAJAGOPALAN, C. K. S., 1974 Disease resistance in tomato against damping-off. - Indian Phytopath. 27: 182-186.

694. MYERS, H. E., 1934 - Effect of chemical soil treatments on the root, crown, and shoot rot of milo. - J. Am. Soc. Agron. 26: 737-739.

695. NAGAICH, B. B. & SINGH, B., 1960 - Damping-off of cucurbitaceous vegetables and its control. - Agra Univ. J. Res., Sci. 9: 125-135.

696. NANCE, N. W., 1939 - Diseases of plants in the United States in 1938. - Pl. Dis. Reptr, Suppl. 119: 120-289.

697. NANCE, N. W., 1940 - Diseases of plants in the United States in 1939. - Pl. Dis. Reptr, Suppl. 128: 210-378.

698. NAPI-ACEDO, G. & EXCONDE, O. R., 1965 - Penetration and infection of corn roots by Pythium arrhenomanes. - Philipp. Agric. 49: 279-293.

699. NATTRASS, R M., 1936 - Annual report of the mycologist for the year 1935. - Rep. Dir. Agric. Cyprus 1935: 57-64.

700. NATTRASS, R. M., 1937 - A first list of Cyprus fungi. - Cyprus Dep. Agric., Nicosia, 87 pp.

701. NEMA, K. G. & MAHMUD, K. A., 1951 - Damping-off of chilli seedlings in Madhya Pradesh due to Pythium aphanidermatum. - Mag. Nagpur agric. Coll. 25(3-4): 10-12.

702. NEMEC, S., 1970a - Pythium sylvaticum pathogenic on strawberry roots. - Pl. Dis. Reptr 54: 416-418.

703. NEMEC, S., 1970b - Fungi associated with strawberry root rot in Illinois. - Mycopath. Mycol. appl. 41: 331-346.

704. NEMEC, S., 1971 - Mode of entry by Pythium perniciosum into strawberry roots. - Phytopathology 61: 711-714.

705. NEMEC, S., 1972 - Histopathology of Pythium-infected strawberry roots. - Can. J. Bot. 50: 1091-1096.

706. NICHOLS, C. W., GARNSEY, S. M., RACKHAM, R. L., GOTAN, S. M. & MAHANNAH, C. N., 1964 - Pythiaceous fungi and plant-parasitic nematodes in California pear orchards. 1. Occurrence and pathogenicity of pythiaceous fungi in orchard soils. - Hilgardia 35: 577-602.

707. NICOLAS, G. & AGGRY, M.,1928 - Un cas intressant de dprissement du persil. - Revue Path. vg. Ent. agric. 1928: 1-2.

708. NIENHAUS, F. & MACK, C., 1974 - Infection of Pythium arrhenomanes in vitro with tobacco mosaic virus and tobacco necrosis virus. - Z. PflKrankh. PflSchutz 81: 728-731.

709. NIRVAN, R S., 1954 - Control of papya foot rot (Pythium aphanidermatum). Indian Phytopath. 6: 47-48 (1953).

710. NITZANY, F. E., 1966 - Synergism between Pythium ultimum and cucumber mosaic virus. - Phytopathology 56: 1386-1389.

711. OCANA, G. & TSAO, P. H., 1966 - A selective agar medium for the direct isolation and enumeration of Phytophthora in soil. - Phytopathology 56: 893 (Abs.).

712. OCFEMIA, G. O., 1939 - A review of sugarcane diseases in the Philippines. - Proc. int. Soc. Sugar Cane Technol. 6: 183-187.

713. ONURAH, P. E., 1973 - Pythium seed decay and stem rot of cowpea (Vigna sinensis) in southern Nigeria. - Pl. Soil 39: 187-191.

714. OTROSINA, W. J. & MARX, D. H., 1975 - Populations of Phytophthora cinnamomi and Pythium spp. under shortleaf and loblolly pines in little leaf disease sites. - Phytopathology 65:1224-1229.

715. OUDEMANS, C. A. J. A., 1919-1924 - Enumeratio systematica fungorum. - Hagae, 5 vols.

716. PALM, B. T., 1932 - Algae as additional hosts of pathogens to angiosperms (preliminary note). - Zentbl. Bakt. ParasitKde, Abt. 2, 87: 229-233.

717. PALM, B. T., 1934 - Notiser om sydsvenska actinomycoser. - Bot. Notiser 1934: 449-465.

717a. PANDOTRA, V. R., GUPTA, J. H. & SASTRY, K. S. M., 1971 - Occurrence of wilt and stemburn of Tephrosia vogelii in India. - Cuff. Sci. 40: 442-443.

718. PAPA, K. E., CAMPBELL, W. A. & HENDRIX, F. F. JR., 1967 - Sexuality in Pythium sylvaticum. - Mycologia 59: 589-595.

719. PARK, D., 1973 - A modified medium for isolation and enumeration of cellulose-decomposing fungi. - Trans. Br. mycol. Soc. 60: 148-151.

720. PARK, D., 1974 - Accumulation of fungi by cellulose exposed in a river. - Trans. Br. mycol. Soc. 63: 437-447.

721. PARK, D., 1975 - A cellulolytic pythiaceous fungus. - Trans. Br. mycol. Soc. 65: 249-257.

722. PARK, D., 1976 - Cellulose decomposition by a pythiaceous fungus. - Trans. Br. mycol. Soc. 66: 65-70.

723. PARK, D., 1977 - Pythium fluminum sp. nov. with one variety and P. uladhum sp. nov. from cellulose in fresh-water habitats. - Trans. Br. mycol. Soc. 69: 225-231.

724. PARK, D.,1980 - A two-year study of numbers of cellulolytic Pythium in river water. - Trans. Br. mycol. Soc. 74: 253-258.

725. PARK, D. & MCKEE, W.,1978 - Cellulolytic Pythium as a component of the river mycoflora. - Trans. Br. mycol. Soc. 71: 251-259.

726. PARK, M., 1934 - Report on the work of the mycological division. - Admin. Rep. Dir. Dep. Agric. Ceylon 1933: D 126-D 133.

727. PARK, M., 1937 - Report on the work of the mycological division. - Admin. Rep. Dir. Dep. Agric. Ceylon 1936: D 28-D 35.

728. PARRIS, G. K., 1940 - A check list of fungi, bacteria, nematodes, and viruses occurring in Hawaii, and their hosts. - Pl. Dis. Reptr, Suppl. 121: 1-91.

729. PARUS, R. VAN, 1960 - Parasitaire schimmels op vlas. - Verh. Rijkssen PlZiekt. Ghent 5: 1-30.

730. PATEL, B. K. & PATE!, A. J., 1976 - Fungi causing damping-off of tomato seedlings.-Indian J. Mycol. Pl. Path. 6: 87-88.

731. PEARSON, R. C. & HALL, D. H., 1973 - Ripe fruit rot of tomato caused by Pythium ultimum and Pythium aphanidermatum. - Pl. Dis. Reptr 57: 1066-1069.

732. PETERSEN, H. E., 1909 - Studier over Ferskvands-Phycomyceter. - Bot. Tidsskr. 29: 345-440.

733. PETERSEN, H. E., 1910 - An account of Danish fresh water Phycomycetes, with biological and systematical remarks. - Annls mycol. 8: 494-560.

734. PETRI, L., 1930 - Unestesa infezione di Pythium su piante di grano. - Boll. Staz. Patol. veg., Ser. 2, 10: 285-301.

735. PETRI, L., 1931 - Rassegna dei casi fitopatologci osservati nel 1930. - Boll. Staz. Patol. veg., Ser. 2, 11: l-50.

736. PIECZARKA, D. J. & ABAWI, G. S., 1975a - Relationship of inoculum density of Pythium ultimum to root rot severity and yield of snap beans. - Proc. Am. phytopath. Soc. 2:104.

737. PIECZARKA, D. J. & ABAWI, G. S., 1975b - Occurrence of Pythium spp. in bean roots and soils in New York State. - Proc. Am. phytopath. Soc. 2: 104.

738. PIECZARKA, D. J. & ABAWI, G. S., 1977 - Synergistic interaction between Pythium ultimum and Fusarium solani f. sp. phaseoli and antagonistic interaction between Pythium ultimum and Rhizoctonia solani on snap beans. - Proc. Am. phytopath. Soc. 4: 124.

739. PIECZARKA, D. J. & ABAWI, G. S., 1978 - Populations and biology of Pytbium species associated with snap bean roots and soils in New York. - Phytopathology 68: 409-416.

740. PLAATS-NITERINK, A. J. VAN DER, 1968 - The occurrence of Pythium in the Netherlands. 1. Heterothallic species. - Acta bot. neerl. 17: 320-329.

741. PLAATS-NITERINK, A. J. VAN DER, 1969 - The occurrence of Pythium in the Netherlands. 2. Another heterothallic species: Pytbium splendens. - Acta bot. neerl. 18: 489-495.

742. PLAATS-NITERINK, A. J. VAN DER, 1972 - The occurrence of Pythium in the Netherlands. 3. Pythium flevoense sp. n. - Acta. bot. neer. 21: 633-639.

743. PLAATS-NITERINK, A. J. VAN DER, 1975 - Species of Pythium in the Netherlands. - Neth. J. Pl. Path. 81: 22-37.

743a. PLAATS-NITERINK, A. J. VAN DER, 1981 - Proposal for additional conservation of the generic name Pythium Pringsheim 1858 vs. Artotrogus Mont. apud Berk. 1845. - Taxon 30: 336.

744. POETEREN, N. VAN, 1930 - Verslag over de werkzaamheden van den Plantenziektenkundigen Dienst in het jaar 1929. - Versl. Meded. PlZiektenk. Dienst Wageningen 62: 1-142.

745. POETEREN, N. VAN, 1937 - Verslag over de werkzaamheden van den Plantenziektenkundigen Dienst in het jaar 1936. - Versl. Meded. PlZiektenk. Dienst Wageningen 87: 84 pp.

746. POETEREN, N. VAN, 1938 - Verslag over de werkzaamheden van den Plantenzektenkundigen Dienst in het jaar 1937. - Versl. Meded. PlZiektenk. Dienst Wageningen 89: 92 pp.

747. POITRAS, W., 1949 - A new aquatic species of Pythium. - Mycologia 41: 171-176.

748. PONTIS VIDELA, R E., 1951 - Una podredumbre del tallo del maz (Zea mays) en Venezuela causada por Pythium aphanidermatum. - Agron. trop. Maracay 1: 13-28.

749. PONTIS VIDELA, R E., 1952 - Una podredumbre de la caraota (Phaseolus vulgaris) eri Venezuela, causada por Pythium aphanidermatum. - Agron. trop. Maracay 2: 207-209.

750. POOLE, R. F., 1934 - Sweet potato ring rot caused by Pythium ultimum. Phytopathology 24:807-814.

751. PORTER, D. M., 1970 - Peanut wilt caused by Pythium myriotylum. - Phytopathology 60: 393-394.

752. PORTER, R. H., 1946 - Germinability of treated and untreated lots of vegetable seed n Pythium-infested soil and in the field. - Bull. Iowa agric. Exp. Stn 345: 949-983.

753. POSTHUMUS, A. C., 1973 - Extraction, purifrcation and identifrcation of 3-indoleacetic acid (IAA) from culture filtrates of Pythium sylvaticum. - Neth. J. Pl. Path. 79: 282-284.

754. POWELL, W. M., OWEN, J. H. & CAMPBELL, W. A., 1965 - Association of phycomycetous fungi with peach tree decline in Georgia. - Pl. Dis. Reptr 49: 279.

755. PRATT, B. H., & HEATHER, W. A., 1973 - Recovery of potentially pathogenic Phytophthora and Pythium spp. from native vegetation in Australia. - Aust. J. biol. Sci. 26: 575-582.

756. PRATT, R G. & GREEN, R J. JR., 1971 - The taxonomy and heterothallism of Pythium sylvaticum. - Can. J. Bot. 49: 273-279.

757. PRATT, R. G. & GREEN, R. J. JR., 1973 - The sexuality and population structures of Pythium sytvaticum. - Can. J. Bot. 51: 429-436.

758. PRATT, R. G. & MITCHELL, J. E. 1973a - A new species of Pythium from Wisconsin and Florida isolated from carrots. - Can. J. Bot. 51: 333-339.

759. PRATT, R. G., & MITCHELL, J. E., 1973b - Differential effects of cholesterol in mating thalli of Pythium sylvaticum and Phytophthora capsici. - Can. J. Bot. 51: 595-599.

760. PRINGSHEIM, N., 1857 - Ueber die Befruchtung and Vermehrung der Saprolegneen. - Mber. dt. Akad. Wss. Bertn: 315-330.

761. PRINGSHEIM, N., 1858 - Beitrge zur Morphologie and Systematik der Algen. 2. Die Saprolegneen. - Jb. wss. Bot. 1: 284-306.

762. PUCCI, E., 1969 - Pythium myriotylum agente di marcume dei baccelli di arachide in Tripolitania. - Rivsta Agric. subtrop. trop. 63: 496-499.

763. PYSTINA, K. A., 1973 - (Effect of sterols and vegetable oils on growth and sexual reproduction of fungi of the genus Pythium.) - Mikol. Fitopatol. 7: 493-498.

764. PYSTINA, K. A., 1974 - (Growth of fungi of the genus Pythium cultivated with different nutrient sources.) - Mikol. Fitopatol. 8: 193-200.

765. PYSTINA, K. A., 1975 - (Taxonomy of the genus Pythium). - Nov. Sist. niz. Rast. 12: 213-219.

765a. QUIMIO, T. H. & ABILAY, L. E., 1977 - Pythums from Philippine soils. - Philipp. Phytopath. 13: 54-73.

766. RAABE, R. D., 1978 - Susceptibility of some Proteaceae to Phytophthora cinnamom and Pythium vexans. - Pt. Dis. Reptr 62: 888-889.

767. RAABE, R. D. & HRLIMANN, J. H., 1972 - Control of Pythium root rot in carnations. - Calif. Agric. 26: 4-5.

768. RACIBORSKI, M., 1891 - Pythium dictyosporum, ein neuer Parasit von Spirogyra. - Ariz. Akad. Wiss. Krakau (Rozpr. Akad. Umiejet.) 1891: 283-298.

769. RACIBORSKI, M., 1893 - Pythium dictyosporum nieznany pasorzyt skretnicy (Spirogyra). - Rozpr. Akad. Umiejet. 24: 25-31.

770. RACIBORSKI, M., 1900 - Parasitische Algen and Pilze Javas. - Bot Inst. Buitenzorg 1: l-39.

771. RAGUNATHAN, V., 1968 - Damping-off of green gram, cauliflower, daincha, ragi and clusterbean. - Indian Phytopath. 21: 456-457.

772. RAJAGOPALAN, S., 1963 - Some watermolds from Kansas. - Trans. Kansas Acad. Sci. 66:113-123.

773. RAJAGOPALAN, S. & RAMAKRISHNAN, K., 1964 - Phycomycetes in agricultural soils with special reference to Pythiaceae. l. Techniques of isolation. - J. Madras Univ., Sect. B, 33: 311-341.

774. RAMAKRISHNA, T. S., 1929 - Pythium aphanidermatum on Opuntia dillenii. - Mem. Dep. Agric. India, bot Ser., 16: 191-201.

775. RAMAKRISHNA, T. S., 1949 - The occurrence of Pythium vexans de Bary in South India. - Indian Phytopath. 2: 27-30.

776. RAMAKRISHNA, T. S., 1955 - Diseases of ornamental plants in Madras State. - South Indian Hort. 3: 39-45.

777. RAMAKRISHNA, T. S. & SOUMINI, C. K.,1955 - Rhizome and root rot of turmeric caused by Pythium graminicola. - Indian Phytopath. 7: 152-159.

778. RAMA RAO, P., 1970 - Studies on soil fungi. 3. Seasonal variations and distribution in some soils in Andhra Pradesh (India). - Mycopath. Mycol. appl. 40: 277-298.

779. RAMOS, J. C., 1926 - Pythium damping-off of seedlings. - Philipp. Agric. 15: 85.

780. RAMSBOTTOM, J., 1916 - Some notes on the history of the classificatiori of the phycomycetes. - Trans Br. mycol. Soc. 5: 324-350.

781. RAMSEY, G. B., 1939 - Fruit and vegetable diseases on the Chicago market in 1938. - Pl.Dis. Reptr, Suppl. 114: 27-40.

782. RAMSEY, G. B. & WIANT, J. S., 1938 - Diseases of fruits and vegetables observed on the Chicago and New York markets in 1937. - Pl. Dis. Reptr, Suppl. 106: 62-82.

783. RAMSEY, G. B., WIANT, J. S. & LING, G. K. K., 1938 - Market diseases of fruits and vegetables: crucifers and cucurbits. - Misc. Publ. U.S. Dep. Agric. 292: 1-74.

784. RANDS, R D., 1930 - Fungi associated with root rots of sugar cane in the southern United States. - Proc. int Soc. Sugar Cane Technol. 3: 119-13 1.

785. RANDS, R D. & ABBOTT, E. V., 1937 - Root rot of C.P. 28/19 on heavy soils controlled by summer planting. - Sugar Bull. 15: 3-6.

786. RANDS, RD. & ABBOTT, E. V.,1939 - Sugar cane diseases in the United States. - Proc. int. Soc. Sugar Cane Technol. 6: 202-212.

787. RANDS, R D., ABBOTT, E. V. & SUMMERS, E. M., 1936 - Disease resistance tests on sugar cane seedlings and initial selection procedure in the southern United States. - Proc. int. Soc. Sugar Cane Technol. 5: 484-491.

788. RANDS, R. D. & DOPP, E.,1934 - Variability in Pythium arrhenomanes in relation to root rot of sugarcane and corn. - J. agric. Res. 49: 189-221.

789. RANDS, R. D. & DOPP, E., 1938 - Pythium root rot of sugarcane. - Tech. Bull. U.S. Dep. Agric. 666: 1-96.

790. RANGANATHAN, K., SHANMUGAN, K. & MARIMUTHU, T., 1973 - A new root rot of safflower in India. - Sci. Cult 39: 354-355.

791. RANGASWAMI, G., 1962 - Pythiaceous fungi. - Indian Counc. Agric. Res., New Delhi, 276 pp.

792. RAO, B., SCHMITTHENNER, A. F., CALDWELL, R. & ELLETT, C. W., 1978 - Prevalence and virulence of Pythium species associated with root rot of corn in poorly drained soil. - Phytopathology 68: 1557-1563.

793. RAO, P. G. & RAJU, D. G., 1955 - Wilt of Talinum triangulare caused by Pythium aphanidermatum. - Sci. Cult. 20:502-503.

794. RAO, V. G., 1963 - An account of the genus Pythium in India. - Mycopath. Mycol. appl. 21: 45-49.

795. RAO, V. G., 1965 - Some new records of market and storage diseases of vegetables in Bombay Maharashtra. - Mycopath. Mycol. appl. 27: 49-54.

796. RAO, V. G., 1966 - An account of the market and storage diseases of fruits and vegetables in Bombay-Maharashtra (India). - Mycopath. Mycot. appl. 28: 165-176.

797. RAO, V. G., 1969a - Diseases of potato in India. - Labdev. J. Sci. Techriol. 7-B: 254-262.

798. RAO, V. G., 1969b - Fungi on citrus from India. - Sydowia 23: 215-229.

799. RAPER, K. B., 1928 - Studies on the frequency of water molds in the soil. - J. Elisha Mitchell scient. Soc. 44: 133-139.

800. RATHBUN, A. E., 1922 - Root rot of pine seedlings. - Phytopathology 12: 213-220.

801. RATHBUN, A. E., 1923 - Damping-off of taproots of conifers. - Phytopathology 13: 385-390.

802. RATHBUN-GRAVATT, A., 1925 - Direct inoculation of coniferous stems with damping-off fungi. - J. agric. Res. 30: 327-339.

803. RATHBUN-GRAVATT, A., 1931 - Germination loss of coniferous seeds due to parasites - J. agric. Res. 42: 71-92.

804. RAVIiS, A.& BOCCAS., B., 1969 - Premire liste annote des Pythiaces parasites des plantes cultives au Congo. - Cah. La Mabok 7: 41-69.

805. REDDI, G. S., 1972 - Antagonism of soil actinomycetes to some soil-borne plant pathogenic fungi. - Indian Phytopath. 24: 649-657 (1971).

806. REEN, L., 1971a - Studies on the factors influencing virulence and enzyme activity of Pythium spp. on potato tubers. - Indian Phytopath. 24: 74-87.

807. REEN, L., 1971b - Virulence of Pythium spp. on potato tuber and their capacity to produce pectic enzymes. - Indian Phytopath. 24: 88-100.

808. REICHERT, I., 1939 - Palestirie: Diseases of vegetable corps; Palestine: Diseases of fruiting plants (except citrus). - Int. Bull. Pl. Prot. 13: 225M-240M; 277M-293M.

809. REITSMA, J. & SLOOF, W. C., 1950a - A Pythium disease of Basella rubra. - Contr. gen. Agric. Res. Stn Bogor 109: 3-7.

810. REITSMA, J. & SLOOF, W. C., 1950b - Further investigations on Pythium diseases. - Contr. gen. Agric. Res. Stn Bogor 109: 12-21.

811. REMY, E., 1950 - Ober niedere Bodenphycomyceten. - Arch. Mikrobiol. 14: 212-239.

812. RICCI, P. & MESSIAEN, C. M., 1973 - A technique for assaying Pythium in soil. - Abs. 2nd int. Cong. Pl. Path., Univ. Minnesota, Minneapolis: 1063.

813. RIDINGS, W. H., & HARTMAN, R. D., 1976 - Pathogenicity of Pythium myriotylum and other species of Pythium to Caladium derived from shoot tip culture. - Phytopathology 66: 704-709.

814. RISTANOVIĆ, B., 1973 - The population of fungi in Skadar Lake with special emphasis on aquatic phycomycetes. - Mikrobiologija 10: 53-61.

815. ROANE, C. W., & FENNE, S. B., 1955 - Some new plant disease records for Virginia. - Pl. Dis. Reptr 39: 695-696.

816. ROBERTSON, G. I., 1973a - Occurrence of Pythium spp. in New Zealand soils, sands, pumices, and peat, and roots of container-grown plants. - N.Z. Jl agric. Res. 16: 357-365.

817. ROBERTSON, G. I., 1973b - Pathogenicity of Pythium spp. to seeds and seedling roots. - N. Z. Jl agric. Res. 16: 367-373.

818. ROBERTSON, G. I., 1975 - A paper disc technique for the recovery of Pythium spp. from soil or water. - N.Z. Jl agric. Res. 18: 409-410.

819. ROBERTSON, G. I., 1976 - Pythium species in market gardens and their pathogenicity to fourteen vegetable crops. - N.Z. Jl agric. Res. 19: 97-102.

820. ROBERTSON, G. I., 1979 - Pythium erinaceum sp. nov. from wheatfields in Canterbury, New Zealand. - N.Z. Jl Bot. 17: 283-286.

821. ROBISON, B. M., 1970 - Microfungi of sugarcane roots and soil in Jamaica. - Trop. Agric. 47: 23-29.

822. ROGER, L.,1932 - Pythium root rot disease of corn in the Philippine Islands. - Philipp. Agric. 21: 165-176.

823. ROGER, L., 1940 - Sur un chancre de lHva en Cochinchine et au Cambodge: le chancre color d au Pythium complectans. - Inst. Rech. agron. forest. Indochine, Hanoi, 11 pp.

824. ROMAN, J. & KOIKE, H., 1970 - Preliminary studies on the interactions of Pratylenchus brachyurus and Pythium graminicola on sugarcane. - Phytopathology 60: 1541 (Abs.).

825. ROMANOVICH, E. A., 1958 - New disease of pumpkins. - Zashch. Rast Vredit. Bolez. 1958(6): 53-54.

826. RONCADORI, R W., LEHMAN, P. S. & MCCARTER, S. M., 1974 - Effect of Pythium irregulare on cotton growth and yield, and joint action with other soil-borne pathogens. - Phytopathology 64: 1303-1306.

827. ROTH, L. F. & RIKER, A. J., 1943 -Influence of temperature, moisture and soil reaction on the damping-off of red pine seedlings by Pythium and Rhizoctonia. - J. agric. Res. 67: 273-293.

828. ROYLE, D. J. & HICKMAN, C. J.,1964 - Analysis of factors governing in vitro accumulation of zoospores of Pythium aphanidermatum on roots. - 1. Behaviour of zoospores. 2. Substances causing response. - Can. J. Microbiol. 10: 151-162, 201-219.

829. ROZE, E. & CORNU, M., 1869 - Sur deux nouveaux types gnriques pour les familles des Saprolgnies et Pronospores. - Annls Sci. nat., Bot, Sr. 5, 11: 72-91 (Reprod. in Bibl. Ec. haut. tud. Sci. nat 2: 2-12.).

830. RUPPEL, E. G., BARNES, D. K., FREYRE, R H. & SANTIAGO, A., 1964 - Effect of seed protectant and planting depth on Pythium and Rhizoctonia damping-off of Tephrosia vogelii in Puerto Rico. - Pl. Dis. Reptr 48: 714-717.

831. SAALTIWK, G. J., 1969 - Root rot of hyacinths caused by species of Pythium. - Neth. J. Pl. Path. 75: 343-354.

832. SADEBECK, R., 1874 - ber Pythium equiseti. - Verh. bot Ver. Brandenburg 16:116-124.

833. SAKURAI, I., AKIYAMA, K. & SATO, S., 1974 - On the formation and discharge of zoospores of Pythium porphyrae in experimental conditions. - Bull. Tohoku reg. Fish. Res. Lab. 33: 119-127.

834. SALADIWI, J. L., SCHMITTHENNER, A. F. & LARSEN, P. O., 1976 - A study on Pythium species associated with Ohio turfgrasses: Their prevalence and pathogenicity. - Proc. Am. phytopath. Soc. 3: 229.

835. SALADIWI, J. L. & WHITE, D. G.,1975 - Pathogenicity of four Pythium spp. to nine turfgrass cultivars at two temperature regimes. - Proc. Am. phytopath. Soc. 2: 26.

836. SALMON, E. S. & WARE, W. M., 1938 - Department of mycology. - Jl S.E. Agric. Coll. 41: 15-19.

837. SALT, G. A., 1977 - A survey of fungi in cereal roots at Rothamsted, Woburn and Saxmundham. - Rep. Rothamst. exp. Stn 1976(2): 153-168.

838. SALT, G. A., 1979 - The increasing interest in minor pathogens. - Soil-borne Plant Pathogens (Schipper, B. & Gams, W., eds), Acad. Press, London, 289-312.

839. SAWSOME, E., 1963 - Meiosis in Pythium debaryanum and its signifrcance in the life-history of the Biflagellatae. - Trans. Br. mycol. Soc. 46: 63-72.

840. SAWSOME, E., 1966 - Meiosis in the sex organs of the Oomycetes. - Chromosomes today (Darlington, C. D. & Lewis, K. R, eds), Oliver & Boyd, Edinburgh, 1: 77-83.

841. SANTO, G. S. & HOLTZMAWW, O. V., 1970 - Interrelationships of Pratylenchus zeae and Pythium graminicola on sugarcane. - Phytopathology 60: 1536 (Abs.).

842. SAREJAWWI, J. A., DEMETRIADES, S. D. & ZACHOS, D. G., 1950 - A brief report on the plant diseases observed in Greece in 1948 and 1949. - Annls Inst phytopath. Benaki, N. S. 4: 5-7.

843. SASAKI, M. & SATO, S., 1969 - Composition of medium and cultural temperature of Pythium sp., a pathogenic fungus of the Akagusare disease of cultivated Porphyra. - Bull. Tohoku Reg. Fish Res. Lab. 29: 125-132.

844. SAUTHOFF, W. & KRBER, H., 1960 - Ober Pythium-Wurzelfulen an einigen Warmhaus pflanzen. Erreger. Pythium splendens - ein fr Deutschland neuer Pilz. - Gartenwelt 60: 417-419.

845. SAUVE, R. J. & MITCHELL, D. J., 1975 - The influence of oospore density of four Pythium spp. in soil on infection and disease of several hosts. - Proc. Am. phytopath. Soc. 2: 140.

846. SAUVE, R. J. & MITCHELL, D. J., 1977 - An evaluation of methods for obtaining myceliumfree oospores of Pythium aphanidermatum and P. myriotylum. - Can. J. Microbiol. 23: 643-648.

847. SAVULESCU, T., 1940 - Etude systmatique du genre Pythium en Roumanie. - Bull. Acad. Sci. Roumanie, Sect Sci. 23: l-8.

848. SAWADA, K., 1927 - (Descriptive catalogue of the Formosan fungi, 3.) - Dep. Agric. Res. Inst Formosa 27: 1-62.

849. SAWADA, K. 1931 - (List of fungi found in Formosa.) - Gov. Res. Inst Taihoku, Formosa, 103 pp.

850. SAWADA, K. & CHEN, C. C., 1926 - (On the putrefaction disease of Antirrhinum majus). - J. nat. Hist. Soc. Formosa 16: 199-212.

851. SCHENK, A., 1859 - Algologische Mittheilungen 5. - Verh. phys. med. Ges. Wrzburg 9: 12-31.

852. SCHENCK, N. C. & KINLOCH, R A., 1974 - Pathogenic fungi, parasitic nematodes and endomycorrhizal fungi associated with soybean roots in Florida. - Pl. Dis. Reptr 58: 169-173.

853. SCHLSSER E., SHAW, P. D. & GOTTLIEB, D., 1969 - Sterols in species of Pythium. - Arch. Mikrobiol. 66: 147-153.

854. SCHMITTHENNER, A. F., 1962a - Effect of crop rotation on Pythium ultimum and other Pythium species in the soil. - Phytopathology 52: 27 (Abs.).

855. SCHMITTHENNER, A. F., 1962b - Isolation of Pythium from soil particles. - Phytopathology 52: 1133-1138.

856. SCHMITTHENNER, A. F., 1964 - Prevalence and virulence of Phytophthora, Aphanomyces, Pythium, Rhizoctonia and Fusarium isolated from diseased alfalfa seedlings. - Phytopathology 54: 1012-1018.

857. SCHMITTHENNER, A. F., 1972 -Effect of fight and calcium on germination of oospores of Pythium aphanidermatum. - Phytopathology 62: 788 (Abs.).

858. SCHOONEVELDT, J. C. VAN, 1950 - Tapvlakziekten en tapylak behandeling. Bergcultures 19: 163-169.

859. SCHNHAR, S., 1966 - Untersuchungen ber das Vorkommen Keimlingsfule verursachender Bodenpilze in Forstpflanzgrten Baden-Wrttembergs. - Allg. Forst- u. Jagdztg 136: 263-267.

860. SCHROTER, J., 1889 - Die Pilze Schlesiens. - Cohn, F., Kryptog.Fl. Schles. 3: 814 pp.

861. SCHRTER, J., 1897 - Pythiaceae. - Engler & Prantl, nat PflFam. 1(l): 104-105.

862. SCHULTZ, H., 1939 - Untersuchungen ber die Rolle von Pythium-Arten als Erreger der Fukrankheit der Lupine, 1. - Phytopath. Z. 12: 405-420.

863. SCHULTZ, H., 1950 - Untersuchungen ber die Rolle von Pythium-Arten als Erreger der Fukrankheit der Lupine. 2. Ergebnisse von Infektionsversuchen. - Phytopath. Z. 17: 200-214.

864. SCOTT, W. W., 1960a - A study of some soil-inhabiting Phycomycetes from Haiti. - Virginia J. Sci., N. S., 2: 19-24.

865. SCOTT, W. W., 1960b - The fungus flora of agricultural soils in Virginia. 1. Aquatic Phycomycetes. - Virginia J. Sci., N. S., 2: 125-129.

866. SCOTT, W. W. & OBIEN, A. H., 1962 - Aquatic fungi associated with diseased frsh and fish eggs. - Progve Fish Cult 24: 3-14.

867. SECHLER, D. & LUKE, H. H., 1967 - Stand loss of small grains in Florida. - Pl. Dis. Reptr 51: 919-922.

868. SEGURA, B. DE, 1970 - Podredumbre radical de la Macadamia en viveros. - Turrialba 20: 513-514.

869. SEMENIUK, G. & MELHUS, I. E., 1943 - Botany and plant pathology section. - Rep. Iowa agric. Exp. Stn 1942: 128-129.

870. SEMENIUK, G. & WADLEY, B. N., 1948 - Pythium seedling rot and root necrosis of Allium cepa. - Phytopathology 38: 29 (Abs.).

871. SEN, T. N., 1930- Appendix 1. Mycology. - Rep. Dep. Agric. Assam 1929-1930: 457-459.

872. SEN, B. & LAL, S. P., 1969 - Blight of braod bean, a new Pythium disease. - Pl. Dis. Reptr 53: 470-472.

873. SEN, B. & SRIVASTAVA, D. N., 1968 - Factors affecting zoospore production in Pythium aphanidermatum. - Indian Phytopath. 21: 209-211.

874. SERBINOW, I. L., 1912 - Zur Biologie von Pythium perniciosum nov. spec., einem Pilzparasiten der Tabaksmlinge. - Bot Oboz. 28: 1-48.

875. SHAHARE, K. C. & ASTHANA, R. P., 1962 - Rhizome rot of ginger and its control. Indian Phytopath. 15: 77-78.

876. SHANOR, L., 1938 - Observations on the development of anew species of Phytophthora. - J. Elisha Mitchell scient. Soc. 54: 154-162.

877. SHARMA, B. B. & WAHAB, S., 1971 - The in vitro activity of chloramphenicol and streptomycin against Pythium aphanidermatum, cause of cottony-leak in cucurbit fruits. - Ghana J. Sci. 11: 111-113.

878. SHARMA, O. P. & JAIN, A. C., 1967 - Root rot of wheat in Madhya Pradesh. - Indian Phytopath. 20: 267-269.

879. SHARMA, O. P. & NEMA, K. G., 1951-52 - A short note on Pythium aphanidermatum on Linum grandiflorum. - Mag. Nagpur agric. Coll. 26: 17.

880. SHARPLES, A., 1930 - Division of mycology. Annual Report for 1929. - Rep. Dep. Agric. Staits Settlements and Fed. Malaya States, 1929, Gen. Ser. Bull. 3: 62-72.

881. SHEPHERD, E. F. S., 1933 - Root rot of young seedlings. - A. Rep. Bot. Div. Dep. Agric. Mauritius 1932: 32-38.

882. SHEPHERD, E. F. S., 1937 - A revised list of plant diseases occurring in Mauritius - Bull. Dep. Agric. Maurit. 23: 1-14.

883. SHOKES, F. M. & MCCARTER, S. M., 1976 - Occurrence of plant pathogens in irrigation ponds in Southern Georgia. - Proc. Am. phytopath. Soc. 3: 342.

884. SHOKES, F. M. & MCCARTER, S. M., 1977 - A filtration system for extracting plant pathogens from water in surface irrigation ponds. - Proc. Am. phytopath. Soc. 4: 97.

885. SHORT, G. E. & LACY, M. L., 1975 - Seed color in relation to carbohydrate exudation and incidence of seed and seedling rot - Proc. Am. phytopath. Soc. 2: 39.

886. SHUKLA, P. & DWIVEDI, R. P., 1976 - Damping-off disease of sunhemp caused by Pythium aphanidermatum. - Indian J. Mycol. Pl. Path. 6: 178.

887. SIDERIS, C. P., 1931a - Pathological and histological studies on pythiaceous root rots of various agricultural plants. - Phytopath. Z. 3: 137-161.

888. SIDERIS, C. P., 193lb - Taxonomic studies in the family Pythiaceae. 1. Nematosporangium. - Mycologia 23: 252-295.

889. SIDERIS, C. P., 1932 - Taxonomic studies in the family Pythiaceae. 2. Pythium. Mycologia 24: 14-61.

890. SIDERIS, C. P., 1935 - Characteristic plant and fruit diseases of tropical plants caused by Pythiaceous parasites. - Proc. 5th pacific Sci. Cong. 1933, 4: 3329-3335.

891. SIDERIS, C. P. & PAXTON, G. E., 1931 - Pathological, histological and symptomatological studies on pineapple root rots. - Am. J. Bot 18: 465-498.

892. SIEMASZKO, W., 1931 - Phytopathologische Beobachtungen in Polen. 2. - Zentbl. Bakt ParasitKde, Abt 2, 84: 248-251.

893. SIETSMA, J. M. & HASKINS, R. H., 1967 - Further studies on sterol stimulation of sexual reproduction in Pythium. - Can. J. Microbiol. 13: 361-367.

894. SIMMONDS, J. H., 19