N.J. Dix

Production of toxins and wall degrading enzymes by Gliocladium roseum

Preparations of glucanases from Gliocladium roseum Bainier degraded glucans in Botrytis allii Munn hyphae. Increased β1–3 glucanase activity and the formation of chitinase occurred in cultures of B. allii parasitized by G. roseum . These results indicated that the disintegration of hyphal walls during parasitic attack was probably due to heterolytic enzyme action. Substances toxic to the host were detected in parasitized cultures; these were stable, partly, at least, of low molecular weight and effective over short distances only. Coagulation of cytoplasm and disintegration of hyphal walls occurred without physical contact between the hyphae of the two species; coiling of G. roseum hyphae around those of the host was infrequent and penetration rare, indicating that intimate contact between hyphae is not an essential part of the necrotrophic attack.

Changes in relationship between water content and water potential after decay and its significance for fungal successions

Calculations from measurements of water content and corresponding water potentials showed that after decay wood and leaves have higher water potentials compared with undecayed material at the same water content. Improvement in water availability through decay may be one of the principal underlying forces which give direction to fungal successions on various substrata.

Inhibition of fungi by gallic acid in relation to growth on leaves and litter

Gallic acid was inhibitory to many fungi from leaves and soil. Notable exceptions included some Penicillium spp. which grew in solutions containing the acid as a sole source of carbon. Inhibition was correlated with polyphenoloxidase activity and the accumulation of the products of incomplete oxidation in the medium. These products had no effect on Penicillium spp. Several substances from the oxidation of the acid by two fungi have been separated and described. Most of these were inhibitory and in some cases toxic in bioassay tests. Two at least were relatively stable and were only slowly broken down by two bacterium species. Stable substances such as these may play an important role in restricting growth of some species of fungi on leaves and in litter containing the acid. Decomposition of this type of litter may be restricted to tolerant fungi such as some Penicillium spp.

Seasonal analysis of the fungal community on Acer platanoides leaves

Numbers of spores on leaf surfaces of Acer platanoides were low in early summer but increased sharply during August, reaching maximum values during October and November. Germination remained low throughout the sampling period and fluctuations in numbers of germinated spores and the amount of mycelium present on leaf surfaces during the summer indicated that several unsuccessful attempts to colonize the leaves occurred before a larger and more stable community became established in the autumn. These changes appeared to be related to the prevailing environmental conditions which either promoted mycelial growth or caused germinated spores to be lost. Spores were more numerous on adaxial leaf surfaces although germination and hyphal growth tended to be better on the abaxial surface. Total mycelial biomass values were generally greater on adaxial surfaces. Cladosporium spp. dominated the hyphal community numerically and produced the greatest number of germinated spores but other genera contributed larger amounts to the total mycelial biomass on some sample dates. The biomass of the yeast-like forms exceeded that of all the common phylloplane genera combined on all sample dates, with ratios greater than 50:1 being recorded during June and July.

Minimum water potentials for growth of some litter-decomposing agarics and other basidiomycetes

Nine leaf litter-decomposing agarics in the genera Mycena, Marasmius and Collybia failed to grow at low water potentials. Minimum requirements for observable growth ranged from −3.6 to between −6.0 and −7.2 MPa. In this respect they show close similarities with wood-rotting basidiomycetes.

Inhibitory substances in Acer platanoides leaves: Seasonal activity and effects on growth of phylloplane fungi

The leaf surface of Acer platanoides L. was found to be an especially inhospitable environment for the growth of phylloplane fungi during the summer season. Several water-soluble inhibitory substances have been detected in ethyl acetate extracts of leaf washings. These passed rapidly into solution when leaves were wetted and proved active against phylloplane fungi in field and laboratory experiments. One important component was gallic acid, which could account for about half the observed inhibition, but other unidentified potent inhibitors were also present. The inhibitory activity of the washings declined as the season advanced and loss of activity could be correlated with an observed increase in the growth of fungi on the leaf surface during September.

Growth and germination of Trichoderma spp. under the influence of soil fungistasis

The effect of soil fungistasis on the germination and growth of 19 Trichoderma isolates from seven species groups has been measured on four parameters. The most widespread effect was in reducing the final percentage germination but other parameters of many isolates remained unaffected. The potential amount of growth in the presence of fungistasis has been calculated and called the Theoretical Colonization Index. The value of the index, which varied considerably between isolates, was modified by fungistasis mainly through a reduction in the final percentage germination.

Utilization of ferulic acid by microfungi from litter and soil

The utilization of ferulic acid as a sole carbon source by 21 species of microfungi was investigated in shake cultures inoculated with spore suspensions. Species saprophytic on Angiosperm leaf litters showed a wide variation in their ability to metabolize this substrate. The majority of soil and conifer litter inhabiting species examined utilized ferulic acid very readily, the notable exceptions being isolates of Trichoderma viride Pers. ex S. F. Gray, Mucor spp. and Mortierella ramanniana (Moller) Lindemann. Examination of the germination process indicated that the capacity to utilize the phenolic acid was not limited by poor germination in the liquid medium used. In fact, the germination of Mucor, Trichoderma and other fungi may be stimulated by ferulic acid, suggesting that some fungi may possess an adaptation to the presence of phenolic acids whereby initial growth may be stimulated, irrespective of whether they can fully utilize the substrate or not.

Spore germination and germ hyphal growth of microfungi from litter and soil in the presence of ferulic acid

Ferulic acid, a phenolic acid related to lignin, was incorporated into water agar for studies on its effect on the germination of spores of fungi representing several ecological groups from litter and soil. Ferulic acid could inhibit or stimulate germination and hyphal growth, the response of the fungus depending upon its ecological distribution and the concentration of the acid. Soilinhabiting species such as Penicillium spp. and conifer needle saprophytes such as Dothichiza pityophila (Corda) Petrak and Thysanophora penicillioides (Roum.) Kendrick showed stimulation of germination, the latter at high concentrations of ferulic acid, whereas Angiosperm leaf saprophytes were significantly depressed. These results suggest that some soil and conifer litter species show an important adaptation to the presence of this compound, and possibly other similar substances, in the environment.

Tolerance of litter-decomposing agarics to water stress in relation to habitat

Thirty-five litter-decomposing agarics representing several ecological groups were found to be relatively sensitive to water stress. In some cases mycelial response to stress was related to conditions in their natural habitats.