Nematophagous fungi: a new endoparasite intermediate between Myzocytium and Lagenidium

Myzocytium intermedium is described as a new endoparasite of Rhabditis nematodes. It produces laterally biflagellate zoospores which track the host and encyst in the vicinity of the body orifices. Infection of mature nematodes is by means of germ tubes from encysted zoospores which penetrate through the body orifices.The thallus is filamentous, much-branched, and nodular in appearance. At maturity it divides to form numerous segments of irregular size and shape. In the vegetative phase the parasite resembles a Lagenidium. In the sexual stage, however, the young antheridium cannot be distinguished morphologically from either the oogonial or zoosporangial segments. No fertilization tube is produced and the antheridial protoplast migrates through a pore in the common wall to fertilize the oogonium. After fertilization, a thick-walled, smooth, spherical oospore is produced.

Nematophagous fungi: new species of the Lagenidiales endoparasitic on Rhabditis

Two new species of the Lagenidiales endoparasitic on the nematode Rhabditis are reported from Ontario soils. In Myzocytium lenticulare the biflagellate zoospores encyst at any point on the cuticle of the host and penetrate directly through the wall. Sexual reproduction in this species is by oogamy. The antheridial protoplast migrates through a pore in the adjacent wall and fuses with the oogonial protoplast to produce a thick-walled reticulate oospore. In Lagenidium caudatum large biflagellate zoospores encyst at or near the body orifices of the host. Many of the zoospores possess a distinct tail-like appendage. Germination tubes from the encysted zoospores penetrate the body orifices to infect the host. The thallus in this species is distinctive in being composed of narrow, irregular hyphae which fill the host. No sexual stage is known.

Nematophagous fungi: a new Myzocytium

Myzocytium humicola is described as a new nematophagous fungus endoparasitic on Rhabditis. This species possesses unequally biflagellate zoospores. These do not attack the nematodes directly but encyst and produce adhesive buds that attach to the cuticle of passing nematodes. The oogonium is fertilized by the passage of the antheridial protoplasm through a pore in the contiguous wall. The resultant oospore has a thick, smooth or finely roughened wall.

Nematophagous fungi: Rhopalomyces elegans

Rhopalomyces elegans is known to be a parasite of nematode eggs. This species is now found to be capable of capturing and parasitizing both the larval and adult stages of a species of Rhabditis. Penetration from an appressorium is followed by considerable subcuticular growth before death and colonization of the host. The presence of functional anastomoses is demonstrated in the vegetative hyphae of this mucoralean fungus.

Nematophagous fungi: Haptoglossa

Haptoglossa heterospora Drech. is redescribed and compared with H. zoospora, which is described as new. In H. zoospora the contents of the infection thallus cleave to form primary zoospores. The encysted zoospore is homologous with the spherical primary spore of H. heterospora. The secondary glossoid spores are apparently not adhesive as previously claimed. The peculiar shape of glossoid spores is related to a unique mechanism of infection whereby infective tertiary spores are injected into nematodes in an extremely short period of time. Tertiary spores develop into separate thalli.

Nematophagous fungi: Meristacrum

Conidia of Meristacrum asterospermum were found to be forcibly ejected, supporting the position of this fungus in the Entomophthoraceae. Conidia adhering to the integument of a live nematode either penetrate directly by a germ tube or germinate externally and produce secondary conidia. Resting spores germinate and produce a single erect conidiophore similar to those produced by thallodic segments.

Population dynamics of Endogone spores in soil

A flotation–adhesion technique is described for the rapid recovery of Endogone spores using small (5–10 g) soil samples. The method proved 94–98% efficient in the recovery of spores from Ontario soils. Spore counts averaged 20–92 per gram with exceptional individual counts reaching 132. Effects of soil type, soil depth, and "host" plant on spore populations are discussed.

Verticillium albo-atrum and V. dahliae as mycoparasites

Verticillium albo-atrum and V. dahliae, normally serious soil-borne pathogens of higher plants, can behave as destructive mycoparasites. Using Rhopalomyces elegans as the test host it was found that both species could readily penetrate the conidiophore walls and grow profusely in the conidiophores and vesicles. The hyphae of V. dahliae may penetrate from the vesicle through the spore connective and into the developing conidia preventing normal maturation in most cases. The significance of these findings in relation to the persistence of these fungi as soil-borne plant pathogens is discussed.

Nematophagous Hyphomycetes: observations on Harposporium helicoides

The conidia of endoparasitic nematophagous Hyphomycetes ingested by nematodes lodge in either the buccal cavity or the oesophageal lumen. In H. helicoides, however, nematodes have little difficulty in swallowing the conidia, and infection is initiated by the conidia germinating in the gut. The characteristics of H. helicoides in culture are given.

Isolation and maintenance of endoparasitic nematophagous Hyphomycetes

A technique has been developed using differential centrifugation which allows the isolation of endoparasitic nematophagous Hyphomycetes belonging to the genera Harposporium, Meria, Nematoctonus, and Verticillium. Both ingested and adhesive parasites have been isolated by this technique. The method eliminates most of the large-spored predaceous species which usually complicate the recovery of endoparasites. Methods for maintaining endoparasitic fungi in association with nematodes or in pure culture are described.

A NEW SPECIES OF ARACHNIOTUS WITH AN OIDIODENDRON CONIDIAL STATE

A new species of Arachniotus is figured and described. This species, A. striatosporus, is characterized by having fusiform ascospores which appear striate in surface view because of the presence of five to nine more or less longitudinal ridges. The ascospores appear stellate in cross section. The species has a conidial state belonging to the form genus Oidiodendron.

VERTICILLIUM CHLAMYDOSPORIUM AND ITS RELATIONSHIPS TO DIHETEROSPORA, STEMPHYLIOPSIS, AND PAECILOMYCES

Two hyphomycetes with similar aleuriospore states are considered. One, with a Verticillium phialospore state, was validly published as Verticillium chlamydosporium Goddard; Stemphyliopsis ovorum Petch and Diheterospora heterospora Kamyschko are later synonyms. The other has a Paecilomyces phialospore state and was validly published as Diheterospora catenulata Kamyschko. The two species show similarities in cultural habit, morphology, and biological specialization and it is proposed that they be considered under one genus, viz. Diheterospora.