This month Mycological Research News features the naming of a rust hybrid as a nothospecies, presents a synopsis of a revised ascomycete system, and the identity of British cramp balls. The 20 research papers in this issue include ones reporting a natural hybrid between two species of Melampsora rust fungi, the molecular detection of Rhizoctonia solani subgroups, variation in Alternaria alternata on tomato, genes coding for proteins involved in VA mycorrhizal formation, pycniospore cap production in rusts, Phakopsora cuticle penetration, variation in Dothiostroma pini, Aspergillus evolutionary rates in a chemostat, and metal tolerance in Oidiodendron ericoid mycorrhizas. Three papers concern Agaricus bisporus, one on oxalate decarboxylase production, and two on its pathogens. The following new scientific names are introduced: Cornuvesica and Halorosellinia gens. nov.; Melampsora ×columbiana nothosp. nov.; Helicodendron microsporum sp. nov.; Cornuvesica falcata (syn. Ceraotocystis falcata), H. oceanicum (syn. Hypoxylon oceanicum), and Sporisorium andropogonis-finitimi (syn. Ustilago andropogonis-finitimi) combs. nov.

Hybrids of Melampsora medusae and M. occidentalis are herein described as M. ×columbiana. This hybrid taxon is characterized by isolates that generally exhibit morphological intermediacy in uredinial and telial traits, and mixed virulence/avirulence on Populus trichocarpa and P. deltoides, the natural hosts of M. occidentalis and M. medusae, respectively. Hybrids frequently contain ribosomal ITS sequences from both Melampsora species, but discordant isolates were also found, like M. medusae in having a urediniospore equatorial smooth spot, and like M. occidentalis in spine density, and intermediate in urediniospore length. Isolates with hybrid urediniospore morphology but homozygous for ITS sequences from M. medusae or M. occidentalis were also found, suggesting that the primary F1 hybrids have produced F2 and/or backcross progeny. In a 1997 survey of the leaf rust population on hybrid poplar in the Pacific Northwest, this ‘new population’ of Melampsora ×columbiana was the only taxon found. Specimens from nearly a century ago indicate that an older hybrid population is of wide distribution in North America. This ‘older population ‘of Melampsora ×columbiana was found on specimens of all species of Populus in sections Aigeiros and Tacamahaca, and on many of their hybrids, in areas outside the type localities of M. occidentalis and M. medusae. These three Melampsora taxa, M. medusae, M. occidentalis, and M. ×columbiana, are the only ones that occur naturally on sections Aigeiros and Tacamahaca of Populus in North America.

A molecular and morphological investigation of 35 collections of Daldinia from 11 plant species revealed five taxonomic entities of Daldinia in northern Europe. These include Daldinia concentrica, D. cf. fissa, D. grandis, D. loculata and D. cf. petriniae. D. cf. fissa, D. grandis and D. loculata were found exclusively on burnt wood, but they do not form a monophyletic unit in a phylogenetic tree derived from analysis of the ITS sequence of the ribosomal DNA.

We have designed primers for identification of the economically important plant pathogenic Rhizoctonia solani, for AG 2 and for each subgroup and an ecological type of AG 2. These specific primers have been designed based on specific sequences of the ITS regions in the R. solani species complex. The PCR procedure involves amplification of the 5.8S ribosomal DNA and part of the ITS regions, using the designed primers in combination with the general fungal primers ITS1F and ITS4B. Two of the primers amplify under optimal PCR conditions R. solani AG 1, AG 2, AG 3, AG 4, AG 5 and binucleate Rhizoctonia (BNR), and six more primers amplify specifically R. solani AG 2, the subgroups, AG 2-1, AG 2-2 and AG 2-3, and the ecological type AG 2-t. In this study DNAs from R. solani AG 2 and AG 4 growing on infected radish were amplified similarly to DNAs from axenic cultures. PCR detection has time saving advantages over traditional isolation methods for detection of Rhizoctonia on infected plant tissue and provides a powerful tool of identification.

Black mould lesions were caused by Alternaria alternata in 76% of 228 tomato fruit with characteristic sunken black lesions collected from fields of processing tomatoes in California. Analysis of 29 RAPD primers revealed a high level of genetic diversity among the 69 isolates tested. Two major phenetic groups (Group 1 with 55 isolates and Group 2 with 14) were identified independently by PCA and by UPGMA of Jaccard similarity coefficients. Only 34 of 137 RAPD markers were monomorphic for all isolates and the genetic similarity between the two groups was 50%. Co-infection of black mould lesions by genetically distinct strains of A. alternata occurred in two of 10 isolates tested. There was no evidence for geographic clustering of isolates with high levels of genetic similarity, suggesting that isolates are widely dispersed across California. Only one isolate was identified which also caused stem canker disease on a susceptible tomato cv., suggesting that these strains play a minor role in causing black mould on processing tomatoes in California. This isolate and two other known stem canker isolates were clustered together with 11 other isolates in Group 2. Group 2-specific bands were also identified in a survey of seven additional isolates known to produce host-specific toxins.

A molecular study of the mycorrhizal symbiosis between barley and Glomus intraradices used differential display PCR and a synchronous colonization method to identify genes that are differentially expressed in symbiosis. Several PCR products were consistently differentially amplified. PCR amplification of genomic DNA from either G. intraradices or barley as templates showed that three such products were encoded by G. intraradices. Sequence analysis of the deduced amino acid sequences of the fungal fragments, following extension by 3′-RACE, revealed similarities to proteins from higher eukaryotes. One (GINMYC1) shows similarity to TRIP15, a human protein that interacts in a hormone-dependent manner with the thyroid receptor. A second (GINMYC2) is similar to O-linked N-acetylglucosamine transferases from vertebrates, and the third (GINHB1) contains a putative leucine zipper and a homeodomain which indicates that it binds DNA and may act as a transcriptional regulator. Fragments of the expected sizes were amplified by RT–PCR from mRNA of mycorrhizal barley roots for all three fungal cDNAs, which indicates that the corresponding genes are expressed during intraradical growth of G. intraradices. The results provide a promising insight to fungal gene expression early in formation of this compatible and mutualistic symbiosis.

The phylogenetic relationship between Epicoccum nigrum and Phoma epicoccina has been assessed by means of sequencing of the ITS regions of rDNA. The analysis of the sequences from five isolates of E. nigrum and four of P. epicoccina suggests that both entities represent the same biological species.

The genetics of somatic incompatibility in tetrapolar Collybia fusipes was studied using eight dikaryotic isolates collected from the wild and their experimentally derived progeny. Monokaryons from each isolate were all paired with the same unrelated monokaryon and also paired together in all combinations. The somatic compatibility of the two resulting sets of dikaryons was studied. Two different types of somatic incompatible interaction were observed, lightly or heavily pigmented lines developing between the two isolates. The dikaryons that had one nuclear type in common and one coming from sibling monokaryons were compatible in 7–27% of the cases, incompatible with a lightly pigmented interaction in 30–93% and incompatible with a heavily pigmented interaction in 0–53%. The results suggest that at least three to four loci control the somatic incompatibility in C. fusipes, one of them alone controlling the heavily pigmented interaction.

Pycnial nectar of one mating type is known to induce cap formation on pycniospores of opposite mating type within several species of Puccinia and Uromyces. To learn if caps are induced by nectar transfers between species, we used interspecific pairings involving six species of Puccinia and three of Uromyces. Overall, caps were induced in 14 pairings between different species involving all tested species, except Puccinia helianthi which has no intraspecific cap induction. Nectar (with pycniospores) exchanged in reciprocal transfers between individual pycnial clusters of two different species gave pycniospore caps in nine of 16 cluster pairings, comparable to rates within species. Spore-free nectar combined from five or more pycnial clusters of one species (to ensure that nectar of two mating types was present) usually induced caps in pycniospores from single pycnial clusters of a second species. This occurred in all tested pairings of species except pairings involving P. helianthi. In experiments with pycniospore-free nectar of one capping type specificity from P. recondita, caps were induced in about 50% of pycnial clusters of unknown capping type from P. triticina or P. hordei and only in pycnial clusters of one capping type from P. triticina or P. reichertii in experiments in which type within species was determined. Coupled with the fact that capping type specificity and mating types are coincident within species, the results indicate that mating type-specific induction of pycniospore caps by nectar extends across species boundaries. Although aecia were never produced in interspecific pairings, cap induction occurred as it does in intraspecific pairings where it precedes aecium formation in species exhibiting the capping phenomenon.

Urediospore-derived infection structures of Phakopsora apoda, a rust fungus on kikuyu grass (Pennisetum clandestinum), penetrate the host leaf directly through the cuticle and not through the stomata. A urediospore germinates on the leaf to form a short germ tube which is delimited from a terminal appressorium by a septum. Most appressoria form at the junctions between epidermal cells. Appressoria are often sessile to the urediospores. From the base of the appressorium, a penetration peg develops, which penetrates through the host cuticle and epidermal cell wall. Penetration of the epidermal cell wall occurs approx. 6 h post inoculation. Once inside the epidermal cell, the penetration peg expands to form a penetration hypha, which traverses the epidermal cell and emerges into the intercellular space of the mesophyll tissue. A septum is formed in the intercellular portion of the penetration hypha, delimiting a primary hypha which extends further into the mesophyll, before branching to form two secondary hyphae. This penetration process appears to be very similar to that of Phakopsora pachyrhizi on soybean.

The forest pathogen Dothistroma pini (Scirrhia pini) infects the needles of many pine species, causing needle loss and consequently retarded wood growth. Only one strain of Dothistroma pini is present in New Zealand. Because over 90% of commercial forests in New Zealand are planted with the susceptible species Pinus radiata, a study of the global diversity of D. pini strains was initiated to assess the threat of further unwanted introductions of the pathogen. A collection of D. pini strains from eight countries was studied in the UK. The production of dothistromin toxin by the strains, and DNA sequence analysis of the ribosomal ITS region, confirmed their identification as D. pini, although strains from the central USA contained two nucleotide substitutions in the ITS region. Colony morphologies and growth rates were diverse, but all strains which sporulated showed a similar wide range of spore size. The morphological features examined did not support separation of the strains into the two groups shown by ITS sequences. Most striking was the production, in axenic culture, of extremely high levels of dothistromin toxin by strains from Germany and, to a lesser extent, some from the USA (>500 times and >40 times as much as the New Zealand strain, respectively). The high level of production of dothistromin toxin by some strains is a concern for forest health as well as for forest workers and needs to be evaluated further.

Aspergillus niger and A. nidulans were grown separately in glucose-limited chemostat cultures on modified Vogel's medium. Periodic selection (the appearance of new mutant populations) in A. niger was determined by monitoring oscillations in the concentration of cycloheximide-resistant mycelial fragments in samples from the fermenter vessel. Using these data, the interval between the periodic selection of each new mutant population was 32±6 generations (mean±S.E.M.). Periodic selection in cycloheximide resistance in three morphologically distinct sub-populations of the A. niger culture averaged 36±2, 31±11 and 28±5 generations and these values were not significantly different from that of the whole population (32±6 generations). Also, it was possible to estimate the rate of evolution taking place in these cultures by monitoring oscillations in the frequency of morphological mutants. The intervals between the periodic selection of morphological mutant populations in A. niger and A. nidulans were 28±3 and 22±2 generations respectively.

Ericoid mycorrhizal fungi can alleviate heavy metal toxicity to their host plant, but the mechanisms that lie behind this increased tolerance are unknown. As a first step in the characterisation of two isolates of Oidiodendron maius from mycorrhizal roots of Vaccinium myrtillus growing in heavily contaminated soils, we investigated their taxonomic position, their mycorrhizal capabilities and their ability to grow in the presence of heavy metals. When growth was compared with isolates from non-polluted soils, a better performance was observed in the presence of increasing concentrations of zinc salts, especially at higher ion concentrations. The mechanisms of tolerance may include the production of mucilage and extracellular pigments.

Oxalate decarboxylase activity was present in liquid culture medium and mycelium of Agaricus bisporus. Enzyme activity in the mycelium peaked at two-weekly intervals after primary growth phase and into secondary metabolism, with activity peaks in the medium occurring 7 d later than in the mycelium. The enzyme was partially purified and had two isozymes with pIs 3.0 and 3.4. Characterization of the protein by SDS–PAGE and Western blotting against a polyclonal antibody raised to oxalate decarboxylase from Collybia velutipes showed a major protein band of 64 kDa. Oxalate decarboxylase was also detected in the fruit body up to the cup stage of development. The pH optimum for the enzyme was 3.6 and temperature optimum was 35 °C.

The discoloration of A. bisporus after infection by Pseudomonas tolaasii, P. gingeri, P. agarici, P. reactans, Verticillium fungicola and Trichoderma harzianum can be distinguished by chromametric measurements. Infection with P. tolaasii caused a specific colour change, independent of the bacterial concentration applied (ΔL = 54.7, Δa = 16.6, Δb = 28.7%). The colour change provoked by P. gingeri had a characteristic profile different from P. tolaasii (ΔL = 36.3, Δa = 14.1, Δb = 49.5%). P. agarici and P. reactans provoked only a slight increase of red colour. Response to T. harzianum was orange, and to V. fungicola brown, similar to P. tolaasii but paler and more yellowish. All pathogens except P. reactans provoked degradation of total tyrosinase to variable extents. Activation of tyrosinase was only observed after infection with P. tolaasii (to almost 7%) and V. fungicola (to 3%).

A survey of fungicide resistance among isolates of the mushroom pathogens Cladobotryum mycophilum and C. dendroides Types I and II was undertaken, with respect to the active ingredients thiabendazole, carbendazim (benzimidazoles) and prochloraz manganese following an epidemic in Britain and Ireland in 1994/95. The majority of isolates (41/57) were strongly resistant to thiabendazole (ED50 > 200 ppm) and were exclusively C. dendroides Type II. All C. mycophilum and C. dendroides Type I isolates, and four C. dendroides Type II isolates, were weakly resistant to thiabendazole (ED50 1–10 ppm). Thiabendazole-resistant C. dendroides Type II isolates were only weakly resistant to carbendazim (ED50 2–10 ppm) and isolates which were weakly resistant to thiabendazole were carbendazim-sensitive (ED50 < 1 ppm), demonstrating a lack of complete cross resistance between these two benzimidazole fungicides. The ED50 values for all isolates with respect to prochloraz manganese ranged from 0.14 to 7.8 ppm. Benzimidazole resistance was considered to have been an important factor influencing the severity of the 1994/95 cobweb epidemic but 25% of isolates collected were benzimidazole sensitive.

Most species in Ceratocystiopsis share many characters with species in Ophiostoma. Unlike other Ceratocystiopsis species, C. falcata appears to have enteroblastic conidium development and what appears to be a Chalara anamorph. Morphologically, Cp. falcata is thus more similar to Ceratocystis (with Chalara anamorphs) than Ophiostoma, although it is very distinct from Ceratocystis in perithecial characteristics. Recent studies using molecular data have shown that, despite its peripheral similarity to Ceratocystis, Cp. falcata is distantly related to either Ceratocystis or Ophiostoma. In view of this molecular evidence a new genus, Cornuvesica, is described for it, characterized by having falcate, sheathed and septate ascospores. The anamorph of Cornuvesica is morphologically similar to Chalara but conidia are obovoid with only one truncate end. Conidia are apparently not produced by ring wall building and Chalara is not an appropriate genus for it. We suggest that the anamorph of Cornuvesica represents a genus distinct from Chalara.

A new genus, Halorosellinia, is introduced to accommodate the lignicolous mangrove inhabitant Hypoxylon oceanicum. A detailed illustrated account of the teleomorphic and anamorphic states is given. Halorosellinia oceanica comb. nov., is compared with Stilbohypoxylon quisquiliarum and Nemania confluens (a reduced form of Nemania) and the reasons for introducing a new genus are discussed. Data on the ecology and geographical distribution of H. oceanica are presented.

A new aero-aquatic helicosporous hyphomycete, Helicodendron microsporum, is described and illustrated from decaying leaves submerged in a small artificial pond surrounded by Quercus ilex and Pinus halepensis in Mallorca, Spain. It is characterized by branched conidiophores with chains of hyaline conidia eventually forming white clusters which do not break up even at maturity. It also has small conidia (8–10 μm diam.) consisting of a 2–2.5 μm thick filament which coils 1.5–2 times counter-clockwise. The main characters of the species are compared with 14 similar hyalosporous Helicodendron species.

Picoa lefebvrei and Tirmania nivea are reported for the second and first time from Spain and Europe, respectively. They are illustrated and compared with material and descriptions of the related P. juniperi, T. pinoyi and P. lefebvrei is compared with material from Israel. The collection of T. nivea was originally recorded as T. pinoyi, which should, therefore, be removed from the European Catalogue of hypogeous fungi.