Exserohilum longisporum sp. nov., isolated from Miscanthus sinensis, is described and illustrated. Its affinity to closely related species is discussed to show the distinguishing morphological features.

The RAPD technique was used to distinguish two forms of Melampsora rust on Salix viminalis. Fifteen isolates of the stem-infecting form and 19 of the leaf-infecting form collected from the U.K. were tested with 10 arbitrary primers. All the primers generated polymorphic bands and 46 putative loci were examined. Seven primers gave a total of eight bands specific for the stem-infecting form and four primers produced five bands characteristic of the leaf-infecting form. Cluster analysis using Unweighted Pair-Group Method with Averaging (UPGMA) revealed 62% disagreement between the two forms. The RAPD band patterns of the stem-infecting form isolates were almost identical, while those of the leaf-infecting isolates showed up to 29% variation.

Changes in conidial numbers of aquatic hyphomycetes in water passing through a concrete pipe were investigated by water filtration. Retention in the pipe was low and concentrations of conidia of Alatospora acuminata, Anguillospora longissima, Clavariopsis aquatica, Clavatospora longibrachiata, Heliscella stellata, Lemonniera terrestris, Lunulospora curvula, Pyricularia submersa, Tetrachaetum elegans and Tetracladium marchalianum were unchanged after 1·8 km drift. Only one species, Articulospora tetracladia, showed significant decrease, resulting in part from fragmentation of the conidia. These results suggest that studies of communities of aquatic hyphomycetes in natural environments by sampling conidia by water filtration need to account for differences in stream retention as well as species specific differences in conidial fragmentation.

Appressorium formation in vitro by Phytophthora palmivora started after about 1 h of incubation of zoospores in an aqueous solution and was influenced by topographical signals, substrate hydrophobicity and available nutrients. Free floating, non-adhering germlings did not form appressoria. On smooth substrates, no appressoria were formed under high nutrient conditions (20% pea broth) independent of the hydrophobicity of the contact surface, while under low nutrient conditions (5% pea broth) appressoria formed on smooth substrates with hydrophobic, but not on smooth substrates with hydrophilic, surfaces. If the same substrates were scratched, appressoria formed over these scratches independent of levels of exogenous nutrients and substrate hydrophobicity. These findings are summarized in a model of signalling for appressorium induction.

The sensitivity to UV-B (290–320 nm) radiation of common phylloplane yeasts from two contrasting UV-B environments was compared in the laboratory using mixtures of white light (PAR: 400–700 nm) and UV-B radiation from artificial lamp sources. Sporidiobolus salmonicolor, Rhodotorula mucilaginosa and Cryptococcus sp., the dominant yeasts on leaves of tea (Camellia sinensis), were isolated in Sri Lanka (SL), while Sporidiobolus sp. and Bullera alba, dominant on faba bean (Vicia faba), were isolated in the U.K. Dose responses were determined separately for each yeast. UV-B reduced colony forming units (due to cell mortality or inactivation) and colony size (due to reduced multiplication) of all yeasts. The LD50 values and doses causing 50% reduction of cells per colony were higher for SL isolates than U.K. isolates. Results indicated that each yeast is somewhat vulnerable to UV-B doses representative of its natural habitat. The relative insensitivity of SL isolates was shown when SL and U.K. isolates were irradiated simultaneously with the same dose of UV-B. Of the two U.K. yeasts, B. alba was significantly more sensitive than Sporidiobolus sp. to UV-B. Except for R. mucilaginosa from SL, all yeasts demonstrated some photorepair in the presence of white light. White light provided relatively little protection for the U.K. isolate of Sporidiobolus sp. although it allowed increased colony size.

The spectral responses of Sporidiobolus sp. (U.K.) and of B. alba (U.K.) were broadly similar. Wavelengths longer than 320 nm had no measurable effect on colony forming units. However, colony survival was significantly reduced at 310 nm and all shorter wavebands. No colonies were counted at 290 nm or below.

The effects of growth media, temperature, pH and light on the development of four isolates of Coniothyrium minitans (CONIO and CH8 (colony type 3), G4 (colony type 4) and G9 (colony type 5)) were examined. Conidial germination, pycnidial production and hyphal extension rate were initially studied on seven different agar-based growth media at 18–20 °C. Potato-dextrose agar (PDA) and malt extract agar (MEA) consistently gave the greatest conidial germination, pycnidial production and hyphal extension rate for all four isolates. Growth and development on molasses-yeast agar was equivalent to that on PDA and MEA except that hyphal extension rate was slower. Subsequently, the effects of temperature, pH and light on the development of C. minitans were investigated on PDA only. The temperature range of conidial germination and pycnidial production of the four isolates was between 10–25° with the optimum at approximately 20°. Hyphal extension occurred over a greater temperature range, between 4 and 25°, with a maximum extension rate of approximately 3·5 mm d−1 for all isolates occurring between 20–25°. Conidial germination, pycnidial production and hyphal extension occurred over a pH range between 3–8 with optimum values for all growth assessments occurring between pH 4·5 and 5·6. Increasing light period from continuous dark, to 12 h light/12 h dark or continuous light had no effect on conidial germination or extension growth, but significantly increased pycnidial production.

Isolates G4 and G9, previously characterized by sparse production of pycnidia in comparison with CONIO and CH8, consistently exhibited a reduced production of pycnidia on all media, at all temperatures and pH ranges, and all light regimes tested. This demonstrates the stability of this character among these isolates of C. minitans. The significance of these results for improving production of inoculum of this biocontrol agent and in the identification and classification of isolates of C. minitans is discussed.

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.

Wheat bran, cassava bagasse and sugar cane bagasse were shown to be adequate substrates for the growth and aroma production by the mould Ceratocystis fimbriata. Among the nutritive media tested, sugar cane bagasse complemented with a synthetic medium containing glucose (200 g l−1) gave a fruity aroma while the leucine or valine-containing medium gave a strong banana aroma. Aroma production was dependent on growth and the maximum aroma intensity was detected at about the time of the maximum respirometric activity. Twenty-four compounds have been separated by GC headspace analysis and 20 were identified, among them: 1 aldehyde, 7 alcohols, 4 ketones and 8 esters. It was clearly demonstrated that the chromatographic profile of the headspace of the culture was dependent on the substrate used and on the eventual precursor added. When leucine or valine was added to the substrate, the production of total volatiles in the headspace reached values up to tenfold higher than that for ripe bananas. The Gompertz model, a logistic-like equation, was used to fit the integrated CO2 and volatiles production data.

The relationship between hyphal growth and branching of the grape pathogen Botrytis cinerea was determined on solid media containing either glucose, fructose, sucrose, tartaric acid or malic acid. The concentration of the carbon source had little effect on specific growth rate or the specific rate of tip formation, but growth was inhibited at high concentrations of tartaric and malic acids. Hyphal growth unit length and hyphal extension rate increased with increasing sugar concentration and were always significantly greater than values on tartaric or malic acids. The data provide an explanation for colonization patterns of grape berries. Growth will be poor during the period from setting to the onset of ripening, when organic acids are the main carbon source produced by the berry. Following the onset of ripening, the production of sugars provides more favourable carbon sources for the fungus, enabling achievement of higher specific growth rates, greater hyphal extension rates and, hence, greater colonizing potential.

Phaeoramularia braunii sp. nov., P. trigonellae sp. nov., Stenella capparidiicola sp. nov. and S. hyptiantherae sp. nov., collected on Chloroxylum sp., Trigonella foenum-graecum, Capparis zeylanica and Hyptianthera stricta, respectively are described, illustrated and compared with related species.

Monilinia fructigena secretes one molecular form of endo-polygalacturonase (PG) in apple fruits infected by it. This PG, purified from culture filtrate to homogeneity, had an Mr of ca 33000 (SDS electrophoresis) and a pI value of ca 9·75. It had little or no effect on the structural integrity of potato tuber tissues, nor on the viability of apple callus cells in suspension. Modification of the lysine units of the purified enzyme by pyridoxal phosphate resulted in ca 50% decrease in PG activity. PG thus modified appeared to bind to an apple fibre preparation less than did PG not treated with pyridoxal phosphate. Lysine residues may thus be involved in subsites binding this PG to carboxyl groups in the polygalacturonate.

Information on the genetics and metabolism of 4-aminobutyrate (GABA) in yeasts and fungi is reviewed. In spite of ubiquitous occurrence, there is limited information on its function and biological role. Most fungi utilize GABA both as a carbon and a nitrogen source. Fungal endogenous GABA largely originates from the decarboxylation of L-glutamate and is associated with sporulation/spore metabolism. Whatever its source, GABA is catabolized to succinate via succinicsemialdehyde. Taken together these steps define a potential bypass outside the classical tricarboxylic acid cycle. Evidence for the existence of such a functional bypass in fungi is reviewed. The role of GABA and its metabolism in various facets of fungal biology is gradually emerging.

The two forms of acid phosphatase secreted by Botrytis cinerea were purified, characterized and found to possess fundamentally different properties. The phosphate-repressible acid phosphatase was a monomer of clearly defined molecular weight (55–56 kDa), with a polypeptide component of 43 kDa. The enzyme was secreted through the hyphal apex and accumulated in the culture fluid. Its high affinity for a wide range of substrates rendered it suitable for a putative role as an extracellular phosphate-scavenging enzyme. Secretion of a constitutive acid phosphatase occurred at low levels in phosphate-enriched culture; at phosphate starvation, the activity of this enzyme was enhanced ten-fold in the culture fluid and two-fold in the cell wall. The constitutive enzyme had strikingly different properties from those of the repressible form. It consisted of a 93 kDa polypeptide which was heavily glycosylated such that the secreted protein displayed size heterogeneity of 140–200 kDa by SDS–polyacrylamide gel electrophoresis and 320–450 kDa by native Sephacryl S-300 chromatography. Irrespective of the phosphate status, most of the secreted constitutive enzyme activity was retained by the cell wall. These results were consistent with ultrastructural histochemical observations which suggested that this enzyme form was secreted by a novel pathway via the fusion of vacuoles with the plasma membrane in mature hyphal segments.

Aspergillus niger, a fungus capable of citric and oxalic acid production, was grown on solid medium amended with selected insoluble metal compounds (ZnO, Zn3(PO4)2 and Co3(PO4)2). While A. niger was able to grow on and solubilize all three metal compounds, a crystalline precipitate was observed to form eventually in the clear zone of solubilization under and around the colony. These crystals were extracted from the agar, examined by SEM and X-ray micro-analysis and identified as metal oxalates by performance hplc and gas chromatography–mass spectrometry. The ability of A. niger to precipitate other metal oxalates was investigated with cadmium, copper and manganese phosphates and strontium nitrate. Metal oxalates were again produced and it was found that the different metals resulted in different and characteristic crystal morphologies. A. niger is therefore capable of transforming inorganic insoluble metal compounds into organic insoluble metal compounds. The significance of this process as a means of toxic metal immobilization is discussed.

When isolate NIOI of self-inducing Phytophthora boehmeriae was grown on medium containing the fungicide ethazol, the fungus produced oospore-free sectors from which self-sterile cultures were recovered. Self-sterile cultures were also recovered from three of six other isolates tested. Single hyphal fragment cultures and single zoospore cultures derived from these self-sterile cultures were of A1A2, A1, A2, and A0 types. Conversion of self-fertile species of Phytophthora to A1 and A2 types is suggested as another possible evolutionary origin of the two sexes in lower organisms, in addition to previously reported mating type change as a possible origin of sexes.

Twenty-six isolates representing six morphologically similar taxa of Tilletia occurring in the western U.S.A. were compared using randomly amplified polymorphic DNA (RAPD) markers and restriction fragment length polymorphisms (RFLP) of the 5·8 s rDNA and flanking ITS regions. Two distinct clusters were separated in the dendrogram based on the RAPD analysis. One cluster contained isolates of T. controversa, Apera interrupta-infecting isolates of a potentially new species of Tilletia, and isolates of the Bromus-infecting varieties bromi-tectorum and guyotiana of the T. fusca (=T. bromi) complex. The second cluster contained Vulpia-infecting isolates of T. fusca var. fusca. The separation of the Bromus-infecting varieties from the Vulpia-infecting variety of T. fusca was supported by distinct restriction digest phenotypes. The RAPD analysis was more sensitive than the RFLP analysis, and allowed separation of the Bromus-infecting varieties bromi-tectorum and guyotiana corresponding to host specificity shown in previous studies. The presence of genetically distinct populations of T. fusca var. fusca occurring on V. microstachys and V. octoflora is indicated by RAPD and RFLP analyses. Species status of T. togwatii, a bunt infecting Poa reflexa that was previously removed from the T. fusca complex, is also supported by RAPD and RFLP analyses.

In order to facilitate the purification of isocitrate lyase from Aspergillus nidulans, the isocitrate lyase overexpressing strain JCB4a was derived. Isocitrate lyase was purified to homogeneity by the criterion of polyacrylamide gel electrophoresis and anti-isocitrate lyase polyclonal antibodies were raised. Stabilization of purified enzyme, when stored at −20°C, required the addition of 1 mM dithiothreitol (DTT) plus 1 mM ethylenediaminetetraacetate (EDTA). Aspergillus nidulans isocitrate lyase is a multimeric enzyme with a native molecular weight of 240 kDa and composed of four monomers of 59 kDa. The enzyme required 5 mM Mg2+ and 1 mM DTT or cysteine for full activity. EDTA at 1 mM replaced the requirement of a thiol compound for activity. The Km for threo-DS-isocitrate was 0·050 mM, and the enzyme activity was inhibited by succinate, itaconate and structural analogs of glyoxylate as well as by fructose-1,6-bisphosphate.

Armillaria mellea and A. tabescens stimulated the production of perithecia and ascospores of Sordaria fimicola shown by the co-culture, spore-plate, over-agar-culture, and culture broth assay methods. Culture diffusate of Armillaria through cellophane also stimulated perithecium and ascospore production. Among 15 other isolates tested, three Mortierella isolates were significantly stimulative for ascospore production. Four vitamins including biotin and thiamine were also stimulative, and may be related to the effects of these fungi.

An assay based on the competitive polymerase chain reaction (PCR) was developed to quantify Glomus mosseae, an arbuscular mycorrhizal (AM) fungus, within plant roots. Using previously designed G. mosseae specific primers, a heterologous internal standard was constructed by amplifying Pseudomonas DNA under low stringency annealing conditions. Co-amplification of G. mosseae and internal standard DNA within leek root extracts provided accurate quantification of target DNA. Colonization of leek roots by G. mosseae was monitored in a comparative study by competitive PCR and microscopy, a conventional method of quantification. These two methods gave closely parallel data for G. mosseae colonization from three different inoculum levels over a 6 week period. Results indicate that competitive PCR is a sensitive and accurate method of quantification. The major advantage of competitive PCR over microscopy is that it can quantify specific AM fungi.

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.