The issue of Mycological Research News pays tribute to R. W. G. Dennis on the occasion of his ninetieth birthday. The importance of permanent microscopic mounts is also featured.

This month's Mycological Research includes the text of the British Mycological Society's Benefactors' Lecture presented by J. D. Rogers in April and which concerns tropical Xylariaceae. In addition, studies of fungi growing in the most radioactive situation in which they have previously been investigated, inside the damaged reactor building at Chernobyl, are reported.

Molecular studies included concern the detection of Tricholoma matsutake, and variation in isolates of Scytalidium thermophilum. Effects of high frequency aneuploidy mutants in Aspergillus nidulans have been examined. Sclertotial inhibitors have been tested for effects against Coniothyrium mintans, and the responses of VA-mycorrhizal fungi to different exudates compared. Mangrove forest plant endophytes, and fungi decaying camphor trees (Ocotea usambarensis), have been isolated and studied in vitro.

Ultrastructural studies on septal pore caps in genera of Hymenochaetaceae and Lachnocladiaceae, and on conidiogenesis in Cercosporella ugandensis and Pseudocercspora musae are presented. The ecology and world distribution of Barbeyella minutisma is also documented.

Two new species are described: Leptographium sibiricum and Melanconiopsis microspora spp. nov.

The following topics are addressed: the interfaces of the Xylariaceae with related groups and the ‘essence of xylariaceousness’; speciation of Xylariaceae in the tropics; the distribution of Xylariaceae in the tropics; xylariaceous fungi categorized into ecological groups based on substrate type and timing of colonization and on modes of water conservation; xylariaceous fungi as latent pathogens and endophytes; novel morphological features of xylariaceous fungi and their roles under tropical conditions.

Extensive fungal growth has been detected on the walls and other building constructions in the inner parts of the Shelter of the damaged fourth Unit of the Chernobyl Nuclear Power Plant in 1997–98. The mycobiota comprised 37 species of 19 genera. Zygomycetes and ascomycetes were represented by one species each: Mucor plumbeus and Chaetomium globosum, respectively. Two mitosporic fungi commonly found were Cladosporium sphaerospermum and Penicillium hirsutum. Alternaria alternata, Aureobasidium pullulans, Aspergillus versicolor, Acremonium strictum, and Cladosporium herbarum were also encountered. Penicillium ingelheimense, Phialophora melinii, Doratomyces stemonitis and Sydowia polyspora were isolated from the Shelter and are recorded from the Ukraine for the first time. Comparison of the species growing under both severe and relatively weak radioactive contamination revealed a dominance of melanin-containing species in heavily contaminated sites; biodiversity and prevalence coefficients supported this.

Sequences of the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA of ectomycorrhizal fungi were analysed and a specific PCR primer pair for Tricholoma matsutake was designed. Using the primer pair, part of the ITS region of T. matsutake (400 bp) was amplified, but no amplified fragment was detected for other ectomycorrhizal fungi. PCR was performed on DNA extracted from mycorrhizas of T. matsutake and Shiro soil (extramatrical mycelium of T. matsutake and soil complexes) and the 400 bp fragments were also specifically amplified. This indicates that presence of T. matsutake at any of its life stages can be easily confirmed by PCR typing.

Scytalidium thermophilum plays an important role in determining selectivity of compost produced for growing Agaricus bisporus. The objective of this study was to characterise S. thermophilum isolates by random amplified polymorphic DNA (RAPD) analysis and sequence analysis of internally transcribed spacer (ITS) regions of the rDNA, to assess the genetic variation exhibited by this species complex and to compare this with existing morphological and thermogravimetric data. RAPD analysis of 34 isolates from various parts of the world revealed two distinct groups, which could be separated on the basis of the differences in the banding patterns produced with five random primers. Nucleotide sequence analysis of the ITS region, which was ca 536 bp in length, revealed only very minor variation among S. thermophilum isolates examined. Several nucleotide base changes within this region demonstrated variation. Genetic distance values among type 1 and 2 S. thermophilum isolates, as determined by ITS sequence analysis, varied by a value of 0.005%. Molecular analyses carried out in the present study would suggest that isolates within this species complex exhibit genetic differences which correlate well with morphological variation and thermogravimetric data previously determined.

The hfa (high frequency of aneuploidy) mutants of Aspergillus nidulans carry conditional lethal (temperature-sensitive) defects which cause an increased frequency of aneuploids to be produced amongst their asexual progeny. When examined microscopically, most of the mutants grew and divided their nuclei at restrictive temperature, albeit more slowly than the wild-type, and aneuploidy was not attributable to an obvious cell cycle lesion. Exceptions were hfaB3 and hfaL1 which exhibited defects in nuclear division, although neither mutant arrested at a specific point in the cell cycle. Cells carrying hfaB3 contained only a single enlarged nucleus which was often transected (‘cut’) by the first septum and temperature-shift experiments showed that the mutation triggers aneuploidy by causing failure to properly exit mitosis. Although the hfaD1 mutant underwent nuclear division, it differed morphologically from wild-type by exhibiting a hyper-branching phenotype. The original hfaD1 isolate was shown also to carry a second unlinked mutation (designated hurA1) which confers resistance to hydroxyurea and partly alleviates the growth defects imposed by hfaD1.

The formation of sclerotia is inhibited by certain chemicals. These resting fungal structures are also parasitized by mycoparasites. This study reports results of experiments on the effect of four sclerotial inhibitors on the sclerotial mycoparasite Coniothyrium minitans and was carried out in an attempt to determine possible compatibilities between sclerotial inhibitors and mycoparasites. Thioglycolic acid was the most toxic to mycelial growth while its sodium salt was totally non-toxic. Mercaptoethanol and mercaptoethylamine were intermediate. At low concentrations, pycnidial formation by C. minitans was not hindered by any of the compounds tested. All four compounds inhibited the formation of sclerotia in Sclerotinia sclerotiorum. Sclerotia are also parasitized by C. minitans. Na-thioglycolate should be tested further as it had no adverse effect on the mycelial growth and pycnidium formation in C. minitans, while it inhibited extensively the formation of sclerotia in S. sclerotiorum. These data suggest that Na-thioglycolate and C. minitans should be considered for use in integrated control.

Aseptic root exudates were collected from the liquid culture of roots of two host (Daucus carota and Lycopersicum esculentum) and one non-host plant (Beta vulgaris) of arbuscular mycorrhizal (AM) fungi. Exudate was also collected from maize (Zea mays FRB6) seedlings which were grown hydroponically under aseptic conditions. Exudate fractions of host roots stimulated hyphal branching behind any actively growing hyphal tip of three AM fungi tested (Gigaspora gigantea, G. rosea, and Glomus intraradices). Fractionation patterns obtained from C18 Sepak cartridges loaded with carrot root exudates isolated from roots grown under various phosphorus regimes, TLC analyses, and solubility properties of fractionated components, indicated a range of hydrophilic to hydrophobic hyphal branching stimulators. The 50/70% methanol fraction from a C18 cartridge induced hyphal branching patterns of G. gigantea that were dose dependent and were identical to those observed when germinated G. gigantea spores were grown with host roots in dual culture. Exudate fractions from B. vulgaris inhibited hyphal tip growth, but inhibited hyphal tips formed recovery branches which would allow continued fungal growth. These recovery hyphae were also formed when germinated G. gigantea spores were grown in dual culture with sugar beet roots. The recovery branches induced by non-host roots and the prolific branching induced by host roots have ecological implications.

Four halophytes belonging to three dicotyledon families, Acanthaceae, Aizoaceae and Chenopodiaceae, were screened for the presence of fungal endophytes. Thirty-six species of fungi, including some sterile forms, were isolated. Camarosporium species showed some degree of host preference as they were the dominant endophytes of the halophytes of Chenopodiaceae but were absent from the other halophytes. Some genera such as Colletotrichum, Phomopsis, Phyllosticta and Sporormiella were ubiquitous.

The capacities of 24 decay fungi, isolated from living trees and decayed timber of the East African camphor tree, to colonise sapwood and heartwood of living trees was tested. Eight species colonised sapwood, and five colonised heartwood and were viable 12 months after inoculation. It was noteworthy that eight important decay species of the East African camphor timber, including Phellinus senex, which is the dominant heartrot species, failed to invade tissues of living trees. The implications of these findings are discussed in relation to the water content and pH of infected and non-infected tissues as well as some parameters of growth of colonised trees.

Of 47 fungi collected from decaying Ocotea wood, 36 exhibited phenoloxidase activity against gallic acid, 40 exhibited it against tannic acid, 33 possessed laccase and 6 possessed tyrosinase. Thus their capacity to produce ligninolytic enzymes indicated that a high proportion of these fungi could cause white rot in Ocotea wood. It was shown that all 21 fungi tested were capable of causing significant weight loss in Ocotea wood blocks in vitro. Basidiomycetes exhibited the greater capacity to cause decay when compared to non-basidiomycetes. The rank order of species in terms of proportional weight reduction in the wood blocks over four months was: Trametes versicolor (28%), Ganoderma australe (16%), Phellinus sp. 2 (15%), Phellinus senex (10%), Stereum ostreum (10%), Loweporus inflexibilis (9%), Stereum hirsutum (8%), P. gilvus (7%), and Schizophyllum commune (2%). The most aggressive non-basidiomycetes, however, were comparable to S. commune, and these were: Cylindrodendrum album (3%), Cylindrocarpon destructans (2%), Daldinia concentrica (2%) and Nodulisporium sp. (2%).

Among 46 species of fungi isolated from decaying Ocotea wood, growth differed in response to oxygen stress during a 24 d trial. All fungi grew for one week but during the following 17 d, six different growth responses emerged. In 12 species daily growth rates were initially stimulated, then totally inhibited; in 4 high growth rates were maintained over the 24 d period; in 5 growth rates were similar under both aerobic and anaerobic conditions and then stopped under the latter; in 5 growth rates in both treatments were similar during the whole trial period; in 16 growth was retarded before inhibition, and in 4 growth was retarded without being inhibited. Growth of 91% of the fungi able to produce ligninolytic enzymes was significantly inhibited or retarded in the absence of oxygen. The behaviour of the fungi under oxygen stress conditions is discussed regarding their roles in the colonization and decay of stems of standing Ocotea trees. It is concluded that in standing trees, oxygen stress may exert selective pressure during successive colonisation, and that tolerance to oxygen stress favours Phellinus species and Loweporus inflexibilis in becoming the main climax decay species in Ocotea trees.

The ultrastructure of the septal pore cap (SPC) of Asterodon, Asterostroma and Coltricia were examined to establish the taxonomic position of these genera. Asterostroma has dolipores with perforate SPCs and is classified in the Lachnocladiaceae. In contrast, Asterodon and Coltricia have dolipores with imperforate SPCs and belong to the Hymenochaetaceae. Other selected species of genera belonging to the Hymenochaetaceae like Hydnochaete, Coltriciella, Inonotus, Onnia, and Cyclomyces also contained imperforate SPCs. Coltriciella, Inonotus and Cyclomyces moreover presented a lamella of endoplasmic reticulum above the imperforate SPC after chemical fixation. Such a lamella could rarely be observed in Coltricia only after high-pressure freezing and freeze substitution. Cryofixed fungal cells of Cyclomyces and Coltricia showed differences in the architecture of the matrix of the SPC. Coltricia showed a more layered matrix structure than the SPC of Cyclomyces. In addition, transmission- and scanning electron microscopy revealed an indent in the centre of the imperforate SPC of Cyclomyces, indicating a reduced thickness, and resulting into a tented profile in cross-sections.

Fruiting colonies of Phellinus contiguus growing on an agar medium and explants from competent regions of dark-grown colonies were used to investigate differentiation of setae, which are a component of the hymenium. The majority of setae arose laterally from intercalary hyphal compartments. The first sign of seta differentiation was generalized swelling of a portion of the hyphal compartment. On explants 50% of the seta population reached the ensuing rounded tip, pointed tip and brown point stages 36, 52 and 68 h post-excision respectively. The distribution of setae on cut surfaces of explants after incubation for three days was in general similar to that of the much larger total hyphal population. However hyphae close to the source outer surface and on explants from older parts of source colonies had reduced capacity for seta differentiation. The spatial density of setae after three days was increased by addition of glucose to the explantation medium and reduced by addition of ammonium chloride. It is concluded that many of the hyphae near to cut surfaces of explants are competent to form setae and that the number which do so is limited by environment, possibly energy supply.

Results of a transmission and scanning electron microscopy study of the mitosporogenous process in Cercosporella ugandensis are given. The details hitherto deduced from light microscopy concerning mitospore initiation, maturation and secession are confirmed. In addition, an ultrastructural basis, in terms of wall layer deposition, is provided for mitospore maturation, scar structure and development, and mitospore secession. This implies a quite separate mode of delimitation and liberation in comparison to other fungi in the Cercospora-like generic assemblage.

Developmental stages in mitospore production in Pseudocercospora musae were examined by differential interference contrast light microscopy, scanning electron microscopy, and transmission electron microscopy. Mitosporogenous cells consistently originated directly from upper stromatic cells. Concentric bodies were found in both stromatic and mitosporogenous cells. The cell wall of stromatic cells, mitosporogenous cells, and mitospores, consisted of two layers. Mitospore ontogeny was found to be holoblastic and mitospore secession schizolytic. After liberation, the mitosporogenous cell apex and the mitospore base exhibited a half septum consisting of one layer. A central pore, occluded by a Woronin body, was observed in the mitosporogenous locus. Mitosporogenous cells proliferated percurrently. The morphological characteristics of the apex of mitosporogenous cells and the base of liberated mitospores in P. musae is of fundamental value in defining unthickened scars as important criteria for generic separation within the Cercospora-like generic assemblage.

On the basis of all accessible records from the literature and our own field observations and collections, the ecology of the rare myxomycete Barbeyella minutissima is described. Analysis of these data, derived mainly from the Northern Ammergauer Alps (Germany) and the Appalachian Mountains (USA: West Virginia, North Carolina), permit the microhabitat requirements of this myxomycete and its ecological associations with other myxomycetes and bryophytes to be elucidated in some detail. Barbeyella minutissima appears to have a distribution centred in montane spruce-fir forests, where it is regularly associated with three other species of myxomycetes – Colloderma oculatum, Lamproderma columbinum, and Lepidoderma tigrinum. Several leafy liverworts are associated with Barbeyella. Particularly noteworthy is Nowellia curvifolia, which seems to be an indicator organism for this myxomycete. A world distribution map of Barbeyella minutissima is provided, along with conclusions relating to the putative range of the species.

Species of Leptographium are well-known inhabitants of conifers in the Northern Hemisphere, in which they cause a blue-stain. They are also known to be associated with insects, especially bark beetles (Coleoptera: Scolytidae). Surveys of dying stands of Siberian fir (Abies sibirica) have resulted in the consistent isolation of an unknown Leptographium from the galleries of the fir sawyer beetle, Monochamus urussovi (Coleoptera: Cerambycidae). This fungus is responsible for the blue-stain in living trees. Comparison with known species of Leptographium led to the conclusion that it had not been previously described, and the name Leptographium sibiricum sp. nov. is introduced here.