This month Mycological Research News features the role of pathogenic Pythium species in the control of patterns of tree distribution in forests, unravelling the relationships of Rhizoctonia-like fungi, and homothallism in apotheciate lichens.

Amongst the 19 papers in this issue are molecular studies on Leptosphaeria maculans, Fusarium solani and Mortierella alpina. Two isozyme groups are reported within F. graminearum, the xylanases in Agaricus bisporus cultures are compared, and the enzymes of white-rot fungi studied. Effects of heavy metals on ericoid mycorrhizas, and the soluble carbohydrates in Pinus ectomycorrhizas have been analyzed. New data are presented on osmotic pressures and osmolytes, and the factors affecting branching in Neurospora. The endophytes of Rubus, and xylem degradation by Fistulina hepatica are explored. Plant pathological contributions include ones on karyotypes in Pyrenophora, Gibberella and Fusarium on teosinte and maize, and Aphanomyces on peas.

Revisions of Hygrocybe subgen. Hygrocybe in the Greater Antilles, and Harknessia species on Eucalyptus are reported, a new synnematal hyphomycete genus is described, and new species of Corynascus have been discovered.

The following new scientific names are introduced: Siamia gen. nov.; Corynascus sexualis, C. similis, C. verrucosus, Harknessia tasmaniensis, Hygrocybe chimaeroderma and S. luxuriosa spp. nov.; H. calyptriformis var. domingensis and H. konradii var. antillana vars. nov.; H. acutoconica var. microspora (syn. Hygrophorus acutoconicus var. microsporus), H. conica var. brevispora (syn. Hygrophorus nigrescens var. brevisporus), H. luteistipes (syn. Hygrophrus luteistipes) combs. nov.

Amplified Fragment Length Polymorphism (AFLP) analysis has been used to analyse 100 Australian, European and North American isolates of Leptosphaeria maculans. All isolates had distinct AFLP profiles. They could be classified into five types, which had very few AFLP bands in common and corresponded to classifications made previously on the basis of ability to cause stem cankers on Brassica napus (A group), or inability to do so (B group), and on host range. Four isolates had AFLP profiles completely dissimilar to these groups and to each other. Genetic diversity and geographic differentiation were analysed separately within AFLP types 1 and 2. UPGMA analysis of the 66 AFLP type 1 (A group) isolates using 50 polymorphic bands did not provide evidence for clustering according to geographic origin. Non-metric multidimensional scaling (NMDS) analysis suggested that the Australian and European populations were separate adjacent clusters, while the North American population partially overlapped both the others. This geographic differentiation was supported by Wright's fixation index (Fst) analysis. Three measures of genetic variability between isolates within regions (effective number of alleles, gene diversity, and Shannon index) showed that the North American A group isolates were less diverse than those from Australia and Europe. The 21 AFLP type 2 (B group; NA1 sub-group) isolates did not cluster based on geographic region, which was confirmed by NMDS and Fst analysis. There was a similar degree of genetic diversity within A group and the NA1 sub-group of B group isolates. Unlike other techniques, AFLP analysis can readily discriminate between group B isolates of the L. maculans complex that were previously difficult to classify and also provides individual fingerprints for isolates. Isolates of the A group and of the NA1 sub-group of B group could be also distinguished readily by electrophoretic karyotyping, as the latter isolates had more bands smaller than 1.4 Mb than the A group isolates.

PCR amplification revealed length polymorphism of the 3′ region of the SSU rDNA gene among special forms of Fusarium solani. These length polymorphisms were found within each of F. solani f. sp. phaseoli, f. sp. batatas and f. sp. piperis. Nucleotide sequence analysis in this region detected intron-like sequences ranging in size from 408 to 439 bp and one 12 bp. The six 408 to 439 bp intron-like sequences were classified into types I-1 and I-2. The sequence similarity was high within I-1 or I-2 type sequences (84.8% and 81.1 to 92.8%, respectively) compared to that between I-1 and I-2 type sequences (45.7 to 48.5%). Both I-1 and I-2 type sequences had a specific insertion point in the SSU rDNA 3′ region. I-1 type sequences had the characteristics of group I introns: (1) a U at the 5′ splice site of the exon, (2) a G at the 3′ splice site of the intron, and (3) they contained the conserved sequence elements P, Q, R, and S. I-2 type sequences had characteristics: (1) and (2), but they did not have any characteristic (3). The 12 bp intron-like sequence was identical to the part of the 5′ end of I-2 type sequences, and its insertion point was the end of I-2 type sequences. The presence or absence of these intron-like sequences caused the length polymorphism of the SSU rDNA 3′ region of F. solani.

Cellulose-acetate electrophoresis (CAE) was used to investigate isozyme polymorphisms of 34 Group 1 and Group 2 isolates of Fusarium graminearum. Of the 26 enzyme systems screened, alkaline phosphatase, NADP-dependent glutamate dehydrogenase, peptidase D and phosphoglucomutase were found to be suitable for distinguishing members of Group 1 from members of Group 2. A great deal of similarity in the isozyme patterns among the isolates of a same group, independently of geographic origin, indicated that isolates within a given group are descendant from a same ancestral population. Significant differences in the isozyme patterns between the isolates of Group 1 and Group 2 indicated, however, that the two groups were of different ancestry. Group 1 isolates have since been named F. pseudograminearum. Due to the short run time, minimal need of equipment, small sample volume and staining requirements, CAE generally provides a rapid and accurate method for isozyme analysis of Fusarium species.

Employing a single DNA primer targeted to clustered tRNA genes, a PCR system has been developed which can be used to uniquely identify different strains of the zygomycete Mortierella alpina. The procedure enjoys advantages over the RAPD-PCR technique in that the single primer operates robustly within a range of PCR conditions, and can be used successfully for members of many fungal genera. As a result of the tendency of some repetitive DNA elements to integrate near to tRNA gene clusters, the possibility that this technique may be extended to identify new examples of retrotransposons and tRNA-derived short interspersed repetitive elements (SINES) is discussed.

Filamentous fungi and yeasts control cytoplasmic osmotic pressure through ion accumulation and synthesis of compatible osmolytes including polyhydric alcohols (polyols), proline, and trehalose. Authoritative data on the osmotic effects of these compounds were obtained using vapour pressure deficit osmometry. All osmolytes tested were characterised by nonlinear relationships between concentration and osmotic pressure. At high concentrations larger polyols generated higher osmotic pressures than smaller ones, though differences between the osmotic effects of polyols with three, four, five and six carbon atoms were not pronounced at lower (physiological) concentrations. Proline shared a similar relationship between concentration and osmotic pressure with polyols with five carbon atoms, while at concentrations above 0.5 M trehalose generated higher osmotic pressures than any of the polyols tested. Mixtures of trehalose and glycerol boosted osmotic pressure in a synergistic rather than additive fashion. These data provide new clues to the adaptive significance of glycerol accumulation, and also suggest that complex patterns of osmolyte synthesis are not due to differences between the osmotic effects of these compounds.

Growth in Neurospora proceeds by the highly polarised extension of hyphal tips and the formation of new tips (branches). While much attention has been devoted to tip growth, the mechanisms responsible for the decision to form a branch are unknown. One important issue is the degree to which the decision to branch is made independently by each tip, or is under the control of proximal regions of the colony. We address this question by comparing the lengths of branch intervals growing from one branch point. We find significant correlations between such intervals under nearly all circumstances tested. In contrast, we find no significant correlation between branch intervals adjacent in series. The strength of the correlation depends on the qualitative nature of the branches surveyed. Dichotomous/apical branching shows a high degree of correlation while lateral branching shows a weaker but still statistically significant correlation (this difference cannot be explained either by differences between the growth rates or distributions of lengths of branch intervals). We interpret the observed correlations to mean that the decision to form a branch is not independently controlled by the tip where the branch forms. Instead it is determined, at least in part, by factors at or close to the previous branch.

The production and properties of Agaricus bisporus endoxylanase and β-xylosidase were studied in compost and liquid cultures. A. bisporus was grown on minimal medium with solka floc BW40, oat spelt xylan, Whatman CC41 microcrystalline cellulose, D-xylose and D-glucose as carbon sources. Endoxylanase activity and β-xylosidase activity were found during growth with complex carbon sources such as cellulose or xylan and no activity was present with sugars such as glucose or xylose. In compost culture endoxylanase activity increased during and after the button stage of fruit body development and decreased after fruit body harvest. The production of β-xylosidase differed in that it was only detectable during the button stage of development. Using activity staining and preparative IEF, three endoxylanase activities were separated from liquid cultures and three principal endoxylanase activities were separated from compost extract. The pH optima and IEF profiles of these activities were similar. Only one β-xylosidase activity was found in liquid culture, whereas two were found in compost culture; the IEF profiles of the compost activities differed markedly from those of the β-xylosidase found in liquid culture.

Over 600 basidiomycetes were isolated from indigenous forests and commercial Eucalyptus and Pinus plantations in South Africa. One hundred and twenty of the cultures were identified and biochemical tests were done to screen the cultures for characteristics that are favourable for biopulping. Most of the white-rot fungi previously associated with biopulping elsewhere in the world were also isolated in South Africa, as well as an isolate with uniquely regulated ligninolytic systems. Phanerochaete chrysosporium was found to be a natural coloniser of wood chip piles in South Africa.

Ericoid mycorrhizal fungi increase the ability of their host plants to colonise soils polluted with heavy metal ions, although the mechanisms are not clearly understood. Two mycorrhizal mycelia of Oidiodendron maius isolated from contaminated soil were previously shown to tolerate high concentrations of heavy metal ions in the growth medium. The influence of zinc ions on the secretion and activity of polygalacturonase (PG), an extracellular enzyme that hydrolyses the pectin component of the plant cell walls, was investigated because of their significance during saprotrophic growth. Two major PG isoforms expressed both in the absence and in the presence of increasing concentrations of zinc ions were identified. The PG isoforms were purified from the tolerant Oidiodendron strains as well as from ericoid fungal isolates from non-polluted soils. Addition of increasing concentrations of Zn and Cd ions to the purified enzymes resulted in an increase of PG activity of both tolerant and non tolerant O. maius isolates at doses below 1 mM. By contrast, at the same metal ion concentrations PG activity of a sterile isolate from non-polluted soil was unaffected or slightly inhibited. We speculate that the response of PG to heavy metal ions may have been a pre-adaptive factor for the colonisation of polluted soils by O. maius.

In the field, the concentrations of several soluble carbohydrates in mycorrhizas of red pine varied seasonally. Fructose, glucose, sucrose and trehalose concentrations were negatively correlated with soil temperature, while myo-inositol and mannitol concentrations were positively correlated. The patterns for the concentrations of fungal carbohydrates (trehalose and mannitol) were consistent with their previously-reported functions. Trehalose may serve as a storage carbohydrate, accumulating during the winter when host carbohydrate is plentiful and when fungal growth is reduced. In contrast, mannitol may serve a translocatory role, increasing in concentration in warmer months when fungal growth is more rapid and when sporocarps are formed.

The carbohydrates of six species of ectomycorrhizal fungi grown at room temperature and at reduced temperatures were also analysed to determine the extent to which seasonal variation in concentrations of fungal carbohydrates of mycorrhizas may be due to fungal acclimation to temperature. Variation in carbohydrate concentration occurred both among fungal species and due to cooling treatment. The variation due to cooling was relatively small, generally less than the variation among species, and less than the seasonal variation observed in field-collected mycorrhizas. This suggests that seasonal variation in the fungal carbohydrate trehalose in mycorrhizas could possibly be due to shifts in host carbohydrate supply rather than to independent shifts by the fungi in response to temperature. Production of a distinct pattern of carbohydrate concentrations by different ectomycorrhizal fungi suggests that fungal carbohydrates may be of taxonomic significance. This was further demonstrated using discriminant analysis of fungal carbohydrates.

A study was designed to isolate and identify the endophytic mycobiota in leaves and twigs of Rubus spectabilis and R. parviflorus, the long-term goal being biological control of these plants with endophytes. Endophytic fungi were isolated from healthy-looking leaves and twigs collected from each species on Vancouver Island, British Columbia, Canada. More than 90% of the leaves of both species were colonised by endophytes. In addition, one third of the twig samples of each species were also colonised. Most isolates belonged to Phomopsis, and five species were identified and characterised according to morphology of the cultures and fructification structures. All Phomopsis species occurred on both Rubus species, but, one primarily colonised R. parviflorus, whereas another preferentially colonised R. spectabilis. The suitability of the isolated endophytes to inhibit growth of R. spectabilis and R. parviflorus, which compete with conifers in reforestation sites, is discussed.

Sequential effects of colonisation by the wood decaying Fistulina hepatica were examined microscopically in naturally infected and artificially inoculated heartwood of pedunculate oak (Quercus robur). For 6 mo, the deposition of brown materials within parenchyma cells containing hyphae was the only visible effect of colonisation. After 12 mo degradation occurred but was initially confined to parenchyma of xylem rays, in which the secondary cell walls showed helically orientated internal cavities containing hyphae, as in a soft rot. The hyphae were covered with a resinous material and persisted in a herringbone pattern after the secondary walls became heavily degraded. The adjacent libriform wood fibres also showed cavity formation. By contrast fibre-tracheids were mainly affected by a brown rot. uv-microscopy indicated that cell types in which the soft rot mode occurred were rich in syringyl lignin, whereas the brown rot was associated with cells rich in guaiacyl lignin. Thus, the present study shows that F. hepatica possesses dual modes of degradation which appear to correlate with the different lignin composition within cell types of oak.

Contour-clamped homogeneous electric field has been applied to analyse genome size and organisation of two important pathogens of barley, Pyrenophora graminea and P. teres.

Electrophoretic karyotypes of four P. graminea isolates resolved 6–8 chromosomal bands, depending on the isolate, while the one P. teres isolate analysed contained six chromosomal bands. Chromosome length polymorphism was observed among P. graminea isolates. For both fungi the chromosomes ranged from 1.6 to more than 6 Mb, with chromosomes larger than 6 Mb migrating as a single band within the compression zone of the gel.

The fatty acid composition of pea roots with and without the root pathogen Aphanomyces euteiches was studied using whole cell fatty acids (WCFA), phospholipid fatty acids (PLFA) and neutral lipid fatty acids (NLFA). Initial screening for A. euteiches markers using WCFA analysis showed that the fatty acids 14[ratio ]1ω9, 14[ratio ]0, 20[ratio ]4 and 20[ratio ]5 were specific to roots infected with A. euteiches. The amounts of these fatty acids correlated positively with the percentage of the root system containing A. euteiches oospores, suggesting that they could be useful indicators of A. euteiches root-infection levels. Analysis of the composition of phospholipid fatty acids (PLFA) and neutral lipid fatty acids (NLFA) of pea roots with and without A. euteiches showed similar specificity as found with WCFA analysis. PLFAs and NLFAs specific to roots inoculated with A. euteiches were also present in mycelium from pure culture of A. euteiches. The PLFAs 14[ratio ]0, 20[ratio ]4 and 20[ratio ]5 were used to estimate biomass of A. euteiches and the NLFAs 14[ratio ]1ω9, 14[ratio ]0, 20[ratio ]4 and 20[ratio ]5 were used as indicators of energy reserves of the pathogen. The possible use of specific fatty acids to study growth and development of A. euteiches in pea roots is discussed.

Seed samples of maize (Zea mays ssp. mays) from Mexico and of teosintes (Zea spp.), the nearest wild relatives of maize, from Mexico, Guatemala, and Nicaragua were assessed for infection with Fusarium species. Strains similar in morphology to Fusarium moniliforme and F. subglutinans were the most frequent isolates from maize and from teosinte species including Z. diploperennis, Z. luxurians, Z. mays ssp. mexicana, and Z. mays ssp. parviglumis. Analysis of fertility, vegetative compatibility and mycotoxin production identified 63% of the 70 F. moniliforme strains from teosinte as genetically diverse members of Gibberella fujikuroi mating population A, a common pathogen of maize. The F. subglutinans strains from maize and teosinte were similarly genetically diverse, but were not fertile with standard testers of G. fujikuroi mating populations B and E, common pathogens of Poaceae, or of mating population H, which causes pitch canker disease of pine. Fifty-four percent of the 80 F. subglutinans strains were fertile when crossed with female tester strains from teosinte and maize collected in a field at Netzahualcoyotyl in the state of Mexico. These strains from Mexico and Central America may comprise a new and distinct G. fujikuroi mating population, but a strain from the Netzahualcoyotyl field site was fertile with a strain of G. fujikuroi mating population H from California. Thus, F. subglutinans from teosinte and maize may have a close relationship to mating population H from pine.

A key to six taxa of Hygrocybe, subgenus Hygrocybe, sections Chlorophanae and Hygrocybe is provided. One species is new and four species are reported for the first time from the Greater Antilles. The new species is H. chimaeroderma (section Chlorophanae). Hygrocybe acutoconica, H. calyptriformis and H. incolor (section Hygrocybe) are reported for the first time, and two new varieties, H. konradii var. antillana and H. calyptriformis var. domingensis (section Hygrocybe) are described. Three new combinations are made: H. acutoconica var. microspora, H. conica var. brevispora and H. luteistipes (section Hygrocybe).

Three new thermotolerant species of Corynascus isolated from Indian and Argentinian soils are described and illustrated: C. sexualis sp. nov. characterised by small ascospores and the absence of a Myceliophthora anamorph (present in all other species of the genus); C. similis sp. nov. characterised by navicular ascospores with two lateral to sub-terminal germ pores; and C. verrucosus sp. nov. distinguished by the ellipsoid ascospores with two oblique to sub-terminal germ pores. A study to compare the ITS-region sequences of all species of the genus with representative species of related genera demonstrated that this region is very conserved in this group of fungi and of low taxonomic value. A key to the eight species of the genus now known is provided. The molecular data suggest the genus is best placed in the Chaetomiaceae rather than the Ceratostomataceae.

Three Harknessia species are reported on eucalypt leaves from Tasmania, Australia. Harknessia hawaiiensis is a new record for Australia and H. victoriae for Tasmania. Harknessia tasmaniensis is described and illustrated as a new species.

A new synnematous hyphomycete, Siamia luxuriosa gen. et sp. nov., is described from Khao Yai National Park, Thailand. The genus is characterised by having long, dark synnemata, conidiogenous cells with numerous protuberant, cylindrical, thickened unilaterally arranged scars, and long, slightly curved, rostrate, multiseptate conidia. Siamia can be compared with several genera of synnematous hyphomycetes e.g. Phaeoisariopsis, Isariella, Atractilinia or Cercospora.