Verticillium wilt in winter-sown oilseed rape (Brassica napus L. ssp. oleifera), which has not yet been reported in the U.K. but is widespread in Europe, was shown to be caused by the host-specific, ‘near-diploid’ Verticillium longisporum comb. nov. Thirty-one cruciferous isolates (plus one from sugarbeet) of V. longisporum, mainly from oilseed rape from Germany, Sweden, Japan, France and Poland, were characterized and compared with nine typical isolates of V. dahliae and five of V. albo-atrum. Isolates of V. longisporum were distinguished from those of V. dahliae by three morphological characters, i.e. elongate microsclerotia, long conidia (7·1–8·8 μm) and mainly three phialides per node on conidiophores, whereas those of V. dahliae had ±spherical microsclerotia, short conidia (3·5–5·5 μm), and 4–5 phialides per node. Isolates of V. longisporum lacked extracellular polyphenol oxidase activity (p.p.o.); they showed mean conidial nuclear diam. (DAPI fluorescence) of ca 1·85 μm, and ‘near-diploid’ standardized arbitrary DNA values (Feulgen DNA microdensitometry) of 0·89–1·17 (mean, 1·02). For isolates of V. dahliae, extracellular p.p.o. activity was detectable, and the corresponding figures for conidial nuclear diam. were ca 1·16 μm and DNA values of 0·45–0·65 (mean, 0·57), respectively. Using three oligonucleotide primers, isolates of V. longisporum were clearly distinguishable from those of V. dahliae and V. albo-atrum by their RAPD band profiles. Greenhouse pathogenicity tests, employing five winter oilseed rape cvs, confirmed the pathogenicity of V. longisporum, whereas V. dahliae was non-pathogenic. On the basis of all the above characters, this host-specific pathotype, V. longisporum, should now be considered as a distinct species. Evidence is presented to suggest that it may have evolved by parasexual hybridization between a strain of V. albo-atrum and a strain of V. dahliae, thus explaining its ‘near diploid’ state and the origin of four recombinants detected.

During investigations of microfungi occurring on submerged plant material in tropical streams, seven species of Sporoschisma and one species of Sporoschismopsis were recorded. Three are newly described: Sporoschisma parcicuneatum, S. phaeocentri and Sporoschismopsis australiensis. Each of these species is described and illustrated in detail and a synopsis of remaining species of Sporoschismopsis is provided. Generic concepts and connections to teleomorphs are discussed and a key is provided to accepted species in both genera.

Co-inoculation of healthy standing rice plants with compatible isolates of Magnaporthe grisea pathogenic to rice resulted in the production of perithecia on the detached portions of leaf sheaths. The isolates had been obtained from the same lesion on a diseased plant collected in Yunnan Province, China. Perithecia were also produced on dead tissue of leaf sheaths and nodes of standing rice plants in a moist chamber. These results strongly suggest that the teleomorph of M. grisea can occur in the upland rice fields in Yunnan.

The amount of Gaeumannomyces graminis var. tritici inoculum was quantified by slot-blot hybridization assay, using a specific DNA probe, pG158. Estimates of the amount of G. graminis var. tritici DNA in naturally infested and inoculated soils were made and correlated with take-all disease severity as determined by a conventional soil bioassay (expressed as a percentage of seminal roots with G. graminis var. tritici lesions). Disease severity in the glasshouse assay and DNA levels were highly correlated. The level of take-all disease severity in naturally infested soil can be predicted using the equation yi=53·078 log (xi)+88·866, where yi=the predicted value of the disease severity (%) and xi=amount of G. graminis var. tritici DNA (ng) in 100 g soil. The DNA-based assay for quantifying the amount of G. graminis var. tritici has been further developed and improved in terms of the sampling techniques and efficiency. Soils of different types were collected to a depth of 10 cm and organic matter between 0·5–1·4 mm in size was separated from this soil. Using a slot-blot hybridization assay, it was found that G. graminis var. tritici was mostly present in the organic matter fraction greater than a size of 0·5 mm and in soil at a depth of 5 cm. This rapid and reliable DNA-based assay is being used in conjunction with a model of take-all disease development to predict disease levels in the field due to G. graminis var. tritici.

Three fungicolous hyphomycetes are described and illustrated. Anastomyces gen. nov., with the type species A. microsporus sp. nov., is described on ascomata of Apiospora sp. on dead culms of a grass from China. It differs from comparable genera by its fungicolous habitat, sporodochial conidiomata and polylocal conidiogenous cells mostly with 2 loci. Each locus produces one conidium but two conidia formed from the same conidiogenous cells join together to form H-shaped conidia in the earliest stages of their development. Idriella rhododendri sp. nov. grows over other microfungi and is described from leaf litter of Rhododendron ponticum from England. Infundibura adhaerens was found to be commonly associated with ascomata and conidiomata on dead leaves of R. ponticum in England.

Xylomyces is re-examined, the type specimen X. chlamydosporis redescribed and illustrated, and new distribution records are provided. Four new species, X. elegans sp. nov., X. giganteus sp. nov., X. punctatus sp. nov. and X. pusillus sp. nov. are described from wood submerged in freshwater collected in various countries. The chlamydospores of these species are drawn at the same scale as a composite diagram for comparison and each is illustrated with light micrographs. Xylomyces foliicola is regarded as atypical in the genus. A key to the accepted species in Xylomyces is provided.

Based upon studies of type specimens six species of Stemonitales are redescribed and illustrated: Comatricha microcarpa, C. laxa, C. nigricapillitium, Stemonitis fusca and S. nigrescens are critically reviewed and illustrated. Comatricha microcarpa is considered to be a nomen ambiguum, and Stemonitis nigrescens is treated as an extreme form of S. fusca. S. virginiensis is recognized as a rare species distinct from the smaller forms of S. fusca. Comatricha nigricapillitium comb. nov. is proposed for Lamproderma nigricapillitium.

The edible mushroom, Agaricus bisporus, when cultivated commercially derives its nitrogen from the proteins present in compost, much of which is firmly bound to the lignin-humic complex. The proteinases involved in mobilization of nitrogen were studied in both the filtrates of liquid culture and mushroom compost. Proteinase activities were detected in liquid culture filtrates with a range of substrate specificities. One activity with chymotrypsin-like specificity was found by Western blotting to be the 27 kDa serine proteinase previously purified from senescent sporophores. Serine proteinase activity and level in the filtrates rapidly increased during mycelial growth on liquid medium containing humic fraction (extracted from mushroom compost) as sole nitrogen source. Activity and level remained low in filtrates of cultures grown on glutamate or casein. Non-denaturing gel analysis revealed the serine proteinase to be the most prominent proteolytic activity in compost filtrates. Regulation of the activity in compost was indicated by a doubling during the early stages of sporophore growth.

The organic soil horizons of heathland and temperate forest ecosystems are characteristically rich in phenolics, which present barriers to organic N availability to the microflora. The abilities of ectomycorrhizal (ECM), ericoid mycorrhizal and wood decomposing saprotrophic fungi to degrade model compounds representing the insoluble phenolic lignin, and soluble phenolics, which provide physical and chemical barriers respectively to organic N availability, were compared. No clear relationship was found between ability to degrade lignin and soluble phenolics. The presumptive assays indicated that most mycorrhizal fungi have only low abilities to degrade these compounds relative to the wood decomposing fungi. In general, ericoid mycorrhizal fungi were capable of greater phenolic degradation than most ECM species, and degradative ability was associated with production of phenol-oxidizing enzymes. In no case was presumptive degradation of lignin or soluble phenolic, or production of phenol-oxidizing enzymes by mycorrhizal fungi as great as that of the wood decomposing fungi. In the case of the ericoid endophyte Hymenoscyphus ericae, phenol-oxidation was associated with production of an extracellular o-polyphenol oxidase (tyrosinase) which showed optimal activity at a pH of 5–5·5 and temperature of 30°C. The ecological significance of the results is discussed.

In order to investigate the barotolerance of marine fungi and to elucidate their ecological role in the deep sea, high-pressure equipment was built and tested. Cultures of the marine yeasts Debaryomyces hansenii, Rhodotorula rubra and Rhodosporidium sphaerocarpum were inoculated into gas-permeable plastic foil bags and incubated in pressure vessels filled with hydraulic fluid that serves also as an oxygen reservoir. The equipment was used at temperatures from 7° to 34°C and pressures from 0·1 to 80·0 MPa. Comparison of five types of plastic foil showed effects on total cell number in batch culture. An exchange of the hydraulic fluid increased yield by replenishing oxygen, the growth-limiting factor. There were no detectable growth differences between buffered (TRIS, HEPES, imidazole, MES) and unbuffered media and thus unbuffered medium was used. Yeasts were best cultivated in an unbuffered sea-water medium (glucose–peptone–yeast extract) sealed in bags made from polyethylene foil. The fluorocarbon liquid FC-77 provided the best oxygen reservoir owing to its high oxygen and carbon dioxide solubility. An exchange of the hydraulic fluid is not necessary if sensitive growth determination methods are used. All marine yeasts cultivated under simulated deep sea conditions were able to grow at least up to a pressure of 20 MPa, with Rhodotorula rubra and Rhodosporidium sphaerocarpum growing at 40 MPa, corresponding to 4000 m depth. Thus, marine yeasts are able to grow under simulated deep sea conditions and may participate in the degradation of organic matter in the deep sea.

Scolecotheca cornuta gen. et sp. nov. is introduced for a fungus which colonizes and causes lesions on algae which occur on needles of Picea abies in Denmark and elsewhere in Europe. It is characterized by cornute conidiomata and scolecosporous aseptate conidia with a basal lateral appendage. Comparisons are made with other coelomycete genera having cornute to infundibular conidiomata and similar conidial morphology.

A Paraisaria-like fungus isolated from a larva of a cerambycid beetle, Anopolophora oshimana, produced small obovoid conidia from multi-necked conidiogenous cells arising from synnematous conidiophores. In culture, the fungus produced curved Harposporium-like conidia in addition to obovoid conidia. When introduced into nematode-infested cultures, nematodes were infected after ingesting the curved conidia and infection typical of Harposporium, producing curved conidia from globose conidiogenous cells, resulted. Reinfection of beetle larvae by injection of hyphal bodies from pure culture and by contact with conidia from the original host showed pathogenicity to cerambycid larvae.

Two nematode-parasitic isolates of Harposporium are reported to form synanamorphs attributable to the Hirsutella. One is attributed to Harposporium anguillulae, the second is described as a new species, H. cerberi. H. cerberi also produced an arthroconidial synanamorph. In infection studies of nematodes, conidia typical of Harposporium proved to be capable of killing bacterial feeding nematodes (Rhabditis sp.) when ingested. Infective conidia of H. cerberi were located posterior to the oesophageal bulb, while those of H. anguillulae lodged above it. Hirsutella conidia were not observed to be infective or adhesive, and none of the spore forms was capable of infecting either of two species of stylet-bearing nematodes (Aphelenchus sp. and Meloidogyne hapla).

The morphology of gametangia was examined in 43 pairs of isolates (mating types A1×A2; 11 A1 and 24 A2 isolates; five isozyme/electrophoretic types) of Phytophthora cinnamomi. An amphigynous antheridium always formed with each oogonium. However, in 41 of the crosses a proportion (39 had 0·2–10% and two had >30%) of oogonia also consistently had single or multiple paragynous antheridia. Single or multiple paragynous antheridia formed concurrently with amphigynous ones during the period of gametangial production in paired colonies. Where there were multiple paragynous antheridia associated with an oogonium, sometimes additional antheridia formed after fertilization or even after oospores were visible. Developmental studies showed that when meiosis in amphigynous and paragynous antheridia was simultaneous, fertilization tubes developed synchronously from both. However, cytological examination indicated that either a nucleus from an amphigynous or a paragynous antheridium fertilized the oosphere. Observations of paragynous and amphigynous, and amphigynous-only associations suggested that fertilization from either type of antheridium only occurred when meiosis in the oogonium was nearly synchronous with that of the antheridium. Asynchronous meiosis between oogonia and antheridia may contribute to failed fertilization and aborted oospore development. This appears to be the first description of paragynous antheridia in P. cinnamomi and the second observation of oogonia with both paragynous and amphigynous antheridia in a heterothallic Phytophthora species. Moreover, the development of both paragynous and amphigynous antheridia with an oogonium is rare in Phytophthora, as is the development of multiple antheridia. Antheridial variation is a characteristic to be taken into account in isolate identification. Nuclei from paragynous antheridia appear able to fertilize oospheres and therefore, have a role in sexual reproduction.

Strains of Trichoderma harzianum with either elevated or reduced production of cellulase-complex enzymes β-glucosidase and endoglucanase were constructed using uv-light mutagenesis. In tests for rhizosphere competence two of the cellulase minus strains were found to have significantly enhanced rhizosphere competence, whilst two cellulase overproducers were found not to colonize either the rhizosphere or rhizoplane of bean plants. These results indicate that rhizosphere competence of Trichoderma strains is not always associated with extracellular enzyme production.

Metarhizium anisopliae produces chitinolytic enzymes which have been implicated in digestion of the cuticles of the host insect during the infection process. In this study, enzymatically produced fungal protoplasts and whole mycelium have been used to study the cellular location and regulation of these enzymes. Intact mycelium was not significantly induced by soluble carboxymethylated (alkaline) chitin in the production of chitinolytic enzymes. In contrast, enzymatically produced protoplasts of M. anisopliae were highly inducible for these enzymes. At 24 h incubation, chitin induced protoplasts secreted into the medium 76% of total N-acetylglucosaminidase activity, whereas less than 10% of chitinase activity was secreted. At 48 h incubation, however, N-acetylglucosaminidase secretion had dropped to 34% of total activity, while the proportion of chitinase activity secreted by protoplasts continued to rise. By 48 h, the majority of chitinolytic enzyme activity had become cell-bound in both protoplast preparations and whole cells, and in protoplasts, this activity was mainly located in the membrane/developing wall fraction. The influence of the cell wall in the regulation and secretion of these enzymes is discussed.

Sterile dematiaceous fungi are commonly isolated from plant roots. They are often assigned to Mycelium radicis atrovirens, a name originally proposed for black, sterile, fast-growing, pseudomycorrhizal fungi. Dematiaceous fungi isolated from roots may be mutualists, commensalists, or pathogens and, in the absence of sporulation, identification is not possible. Forty-six isolates of dematiaceous fungi from the roots of different hosts and locations were characterized using restriction site mapping of polymerase chain reaction amplified nuclear ribosomal DNA internal transcribed spacers. The restriction site maps were compared to identified dematiaceous mycorrhizal and pseudomycorrhizal fungi. Computer generated trees (UPGMA and parsimony analysis) characterized two unknown isolates as Phialophora finlandia, an ectendomycorrhizal fungus. The majority of the isolates were characterized as Phialocephala fortinii-like. Phialocephala fortinii has been reported as both pathogenic and non-pathogenic in a number of hosts. There was variation within the P. fortinii-like group suggesting intraspecific variation or a species complex.

The coexistence in the same pycnidial conidioma of discrete ampulliform and hyaline conidiogenous cells and integrated conidiogenous cells on filiform, septate conidiophores, is described in Pyrenochaeta dolichi. A new Monodictys-like synanamorph is also reported in this species. Monodictys-like conidia are produced on lateral branches from the vegetative hyphae and germinate through the conidiogenous scar. The taxonomic position of P. dolichi is discussed since there is no suitable place for this fungus in the current systematic schemes for this group of fungi.