Interspecific interactions among tropical and subtropical freshwater fungi

Twenty-seven species of tropical and subtropical fungi isolated from freshw ater were examined for evidence of interspecific interactions, which are im portant in determining the ecological roles of fungi. Evidence for interspe cific interactions was examined by inoculating paired fungi 25 mm apart on the surface of agar plates. The antagonistic activities were different amon g different isolates and even between isolates of the same species, for exa mple, Ophioceras dolichostomum isolated from different origins. Pseudohalon ectria longirostrum and Kirschsteiniothelia elaterascus, which produced pig ment in culture, were strongly inhibitory species. Several aquatic hyphomyc etes seems to be less competitive and less likely to produce antagonistic s ubstances. Competitive abilities were also influenced by the range of enzym es that a fungus produced. For example, Verticillium sp. and Diaporthe sp., which produced only one or two kinds of enzyme, were found to exhibit weak competitive abilities and were easily replaced. The results of competition experiments also showed that slow-extending fungi (e.g., Pseudohalonectria longirastrum and Kirschsteiniothelia elaterascus) were more competitive th an early fast-extending fungi (e.g., Ophioceras dolichostomum and Nectria h aematococca).