Studies on the occurrence and activity of fungi in a wheat-field soil

Abstract

The occurrence and activity of fungi in a wheat-field soil has been investigated by plating techniques and by direct isolation. Over 210 fungi have been isolated. A high proportion of the fungi obtained by hyphal isolation are species which were rare or absent from dilution plates. In contrast to dilution methods, where the most abundant fungi isolated were species of Penicillium, Rhizopus, Mucor, Cladosporium and Fusarium, many fungi obtained from hyphae remain sterile in culture. Rhizoctonia solani, Ophiobolus graminis, Rhizoctonia spp. and several Basidiomycetes were obtained by hyphal isolation. Little difference in fungal count has been found between samples collected at 1 and 3 in., but significantly fewer fungal units were obtained from a subsurface horizon at 6 in. deep. Throughout the year fungi showed a well-marked periodicity, with highest numbers of viable units in the soil during the wet winter period. Both viable spores and viable hyphae were present in low numbers during the dry summer period; some fungi, however, survived the summer as hyphae. Bacterial and Actinomycete counts also showed a similar seasonal periodicity. Cultivation and incorporation of wheat residues with the soil greatly increased fungal numbers and activity, particularly in the neighbourhood of the residues. Bacterial numbers likewise increased greatly after cultivation, but Actinomycetes showed comparatively little change in number. The occurrence and activity of specific fungi are discussed. The data indicate that many species have very short periods of activity in the soil, but are always present.