The nature and mechanisms of successions of fungi in soil and plant litter are discussed, and an autecological study of a basidiomycete used to illustrate some methods of approach.

Arthrowallemia anam. gen. nov., characterized by holothallic conidiogenesis, secession randomly schizolytic, and cylindrical, septate, brown conidia emerging from conspicuous unbranched conidiophores, is described and illustrated. The type species, A. formosa sp. nov., was collected on unidentified decaying leaves in Cuba. Notes on similar genera are given.

As part of an inventory of mycodiversity in the Brazilian Cerrado new coelomycetes were collected and are herein described: Phyllosticta xylopiae-sericeae sp. nov., Dinemasporium duguetiae sp. nov., Harknessia salvertiana sp. nov., Harknessia qualeae sp. nov. on living leaves of Xylopia sericea, Duguetia furfuracea, Salvertia convallariodora, and Qualea grandiflora, respectively. Pseudothiopsella hirtellae is reported on a new host, Hirtella gracilipes, and for the first time illustrated in detail.

Podosphaera clandestina var. cydonia var. nov., Setoerysiphe kashmiriensis sp. nov. and Brasiliomyces kumaonensis sp. nov., collected from Northern India on Cydonia oblonga, Sambucus wightiana and Quercus sp., respectively, are described and illustrated.

Zoospore cysts of four isolates of Aphanomyces euteiches with different host-specific pathogenicity germinated in response to peptone, pea root extract, CaCl2 or gum arabic but, in tests on one isolate, did not respond to several individual sugars, amino acids or polysaccharides. A. euteiches showed differential responses to substances applied at different times in the encystment process. Gum arabic triggered germination only when added to motile zoospores, which it caused to encyst. CaCl2 triggered germination when added to motile zoospores or during vortex-encystment of zoospores, but seldom immediately (<2 min) after encystment. Peptone and pea root extract triggered germination when added to motile zoospores, during vortex-encystment or immediately after encystment, but not ca 20 min after encystment. In comparative tests, Phytophthora parasitica was less stage-specific than A. euteiches, because it germinated in response to gum arabic applied to motile zoospores, during encystment and immediately after encystment.

Zoospore taxis, encystment and germination of A. euteiches and P. parasitica cysts were recorded on pea roots by video microscopy. The speed of germination and pattern of sporeling development on roots were most closely matched by treatment of motile spores with gum arabic in pure culture. The behaviour of A. euteiches conformed to a previous model for Pythium and Phytophthora spp., in which zoospores encyst by recognition of root surface components (simulated by gum arabic), germinate autonomously by a calcium-mediated process (simulated by calcium treatment during vortexing), and the germ-tube produces an assimilative hypha (simulated by peptone or pea root extract).

Enridescalsia gen. nov., characterized by synchronous, polytretic conidiogenous cells and brown euseptate conidia, is described and illustrated from submerged, decaying leaves of Terminalia cattapa from Cuba. Notes on similar genera are given.

Ophiostoma ulmi and O. novo-ulmi are partly reproductively isolated, morphologically, behaviourally and molecularly distinct species responsible for the first and current pandemics of Dutch elm disease, respectively. Among >11000 isolates sampled from Dutch elm disease sites across Eurasia and North America since 1973, nine could not be assigned to O. ulmi or O. novo-ulmi. Of these isolates one (P129) was from Poland and eight (d10, d11, e12, e27, e28, e37, f30 and g3) were from a single bark sample in Portugal. These nine isolates were termed ‘fast-waxy’ isolates because of their unusual cultural characteristics. The possibility that they were interspecific hybrids was investigated. When compared with O. ulmi and O. novo-ulmi for colony pattern, growth-rate, optimum temperature for growth, vascular wilt ability, elm bark colonizing ability, cerato-ulmin toxin production, ability to fertilize (as [male ]) O. novo-ulmi, and ability to be fertilized (as [female]) by O. ulmi, they exhibited a combination of O. ulmi-like, O. novo-ulmi-like, intermediate or novel characters (female sterility) consistent with their being hybrids. P129 and representative Portuguese isolates d10 and e27 each exhibited a different combination of characters, indicating each was a different hybrid genotype. When d10 and e27 were independently crossed to the same O. novo-ulmi isolate, differences in their F1 progeny sets for growth-rate and pathogenicity distributions were consistent with their being different recombinant genotypes. A molecular analysis of P129, d10 and e27 using RAPDs of genomic DNA, rDNA RFLPs and cerato-ulmin gene sequences confirmed that each was a unique interspecific hybrid. The mechanism of origin of these hybrids and their evolutionary significance are discussed. Combined experimental and circumstantial evidence indicates that they are relatively unfit, rare and probably transient, and that they arise when O. novo-ulmi invades territory occupied by O. ulmi and replaces it. Nonetheless, the possibility that the hybrids act as a genetic bridge, facilitating transfer of novel vegetative compatibility loci and other loci form O. ulmi to O. novo-ulmi at recent epidemic fronts, requires investigation.

Descriptions and illustrations are provided of two hyphomycete new species from rain forests in Cuba: Dictyochaeta uncinata anam. sp. nov. with setae and conidiophores arising from the same lobed cell and uncinate, filiform conidia, and Helicoma pulchra anam. sp. nov. with helicoid, multiseptate, darkly pigmented conidia. They are compared and contrasted with similar species.

We determined the occurrence of birth rust fungus (Melampsoridium betulinum) within mature mountain birch (Betula pubescens var. czerepanovii) trees and compared the airborne urediniospore concentrations with overall rust infection levels over five successive years. Fifteen groups of three trees 3–5 m high were chosen from a homogenous mountain birch stand. Each group contained a tree with ‘low’, ‘moderate’ and ‘high’ infection covering the natural range of infection levels. The difference in rust classes remained constant throughout the study; trees in class ‘high’ consistently had always highest infection levels and trees in class ‘low’ always the lowest infection levels. Infection levels remained constant between years in ‘low’ class, while the infection levels varied significantly between years in ‘moderate’ and ‘high’ classes. The incidence of disease caused by M. betulinum varied from year to year and was correlated with the total airborne urediniospore counts. The data indicate that trees differ in resistance to birch rust and that infection levels of susceptible compared to resistant trees are more dependent on environmental conditions.

The formation of oxidases and peroxidases by newly isolated ectomycorrhizal fungi was examined with agar spot tests for tyrosinase, laccase, polyphenol oxidase and peroxidase as well as with the Bavendamm test. Extracellular peroxidase was released by virtually all isolates. Tyrosinase (taken as cresolase) was presumably intracellular and occurred in the majority of isolates. The strong laccase reaction was predominantly extracellular, although in some ectomycorrhizal genera the intracellular laccase seemed to dominate. Polyphenol oxidase, as the catecholase/monophenol monooxygenase complex, was found in all isolates although its detection was complicated in the presence of laccase. Lactarius and Russula and the possibly more saprotrophic Morchella showed the most intense enzyme reactions. A comparison with wood and litter decaying fungi indicated that at least some species of several ectomycorrhizal genera possess extracellular oxidative enzymes that are normally characteristic of white rot fungi. It is concluded that mycorrhizal fungi grown asymbiotically can release extracellular enzymes capable of oxidizing a wide range of aromatic compounds.

A technique based on the polymerase chain reaction (PCR) for the specific detection of Phytophthora medicaginis was developed using nucleotide sequence information of the ribosomal DNA (rDNA) regions. The complete IGS 2 region between the 5 S gene of one rDNA repeat and the small subunit of the adjacent repeat was sequenced for P. medicaginis and related species. The entire nucleotide sequence length of the IGS 2 of P. medicaginis was 3566 bp. A pair of oligonucleotide primers (PPED04 and PPED05), which allowed amplification of a specific fragment (364 bp) within the IGS 2 of P. medicaginis using the PCR, was designed. Specific amplification of this fragment from P. medicaginis was highly sensitive, detecting template DNA as low as 4 ng and in a host-pathogen DNA ratio of 1000000: 1. Specific PCR amplification using PPED04 and PPED05 was successful in detecting P. medicaginis in lucerne stems infected under glasshouse conditions and field infected lucerne roots. The procedures developed in this work have application to improved identification and detection of a wide range of Phytophthora spp. in plants and soil.

The utilization profile of 49 carbohydrates, based on API 50 CH biochemical tests, was used for the identification and the discrimination of 75 isolates of Beauveria and Tolypocladium. The data were used to construct a most parsimonious tree in which Beauveria and Tolypocladium were separated into two main branches. Although the Beauveria isolates could not be separated at the species level, eight different clusters corresponding to the eight Tolypocladium species studied were revealed. The reproducible carbohydrate utilization profiles of B. bassiana, B. brongniartii, T. cylindrosporum, T. niveum, T. geodes and T. tundrense have permitted the construction of an identification key that could serve as a tool to complement the morphological description of selected Beauveria and Tolypocladium isolates for their correct identification at the species level. The API 50 CH method is time-saving and can complement effectively more classical techniques for the discrimination between Beauveria and Tolypocladium and for the taxonomy of Tolypocladium at the species level.

Fifty-five strains of Phanerochaete chrysosporium were isolated in South Africa, and screened for indicators of ligninolytic activity: lignin peroxidase (LiP), manganese peroxidase (MnP) and glyoxal oxidase (GLOX). MnP-production as a function of time was followed in all strains. Nine strains were selected for quantification of MnP, LiP and GLOX activities. Statistically significant variation in MnP and GLOX activities existed among the different strains. Under low nitrogen, LiP activity of selected strains showed no significant variation, whereas strain PP25 had significantly increased LiP levels under high nitrogen conditions. Probing genomic DNA with the genes encoding lignin peroxidase (lipD and lipI1), manganese peroxidase (mnp2), and glyoxal oxidase (glox) showed significant genetic diversity with lignin peroxidase and manganese peroxidase probes, but not with the glyoxal oxidase probe.

Mycelial interactions on Hagem agar between 156 isolates of Stereum sanguinolentum obtained from wounded Picea abies or from slash in 12 sample plots located in Sweden, Finland and Lithuania revealed 97 vegetative compatibility groups (VCGs). Of the 23 VCGs that consisted of two or more (maximum, 23) isolates, 13 came from different sample plots, and sometimes from two or all three countries, whereas 10 were confined to a single sample plot. Some variation was observed in cultural characteristics among isolates belonging to the same VCG. Within a sample plot compatible isolates were randomly distributed indicating that distances up to 180 m in a forest stand have little influence on spread of S. sanguinolentum VCGs. Proportions of compatible pairings decreased among isolates collected within the bigger spatial scale. Occurrence of compatibility and consequent grouping of the isolates into VCGs was more pronounced in Swedish populations then Finnish and Lithuanian populations.

Cultures derived from ascospores of an Orbilia, described as a new species, O. fimicoloides, from small mammal droppings, developed conidia of Dactylella cf. oxyspora. This connection is discussed in relation to the anamorph–teleomorph connections of nematophagous fungi classified in the anamorph genera Arthrobotrys and Dactylella.

This listing covers the period January 1, 1997 through to February 28, 1997. Citations are arranged in groups which roughly correspond with the British Mycological Society's Special Interest Committees.

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