Antifungal Activity of Western Australian Soil Actinomycetes against Phytophthora and Pythium Species and a Mycorrhizal Fungus, Laccaria laccata

Abstract

Soil pH, soil moisture content and soil organic matter content did not appear to influence significantly the total numbers of actinomycetes isolated from sample sites in Western Australia. However, seasonal influences exist with summer conditions leading to higher spore isolation. Substantial but non-specific antifungal activity against Phytophthora cinnamomi, P. cryptogea, P. nicotiana, Pythium proli/erum and L. laccata was detected in vitro from many of the 2367 actinomycetes isolated. Antifungal activity mayor may not occur in members of the same actinomycete group, suggesting segregation of antifungal capacity within all groups. A limited number of actinomycete groups was isolated from the rhizosphere of plants and these exhibited similar properties to their counterparts in soil or litter. Actinomycetes isolated from the rhizosphere of Pinus radiata produced a high degree of in vitro antifungal activity against the Phytophthora species but, in general, actinomycetes isolated from root surfaces exhibited antibiosis against all the fungi tested. More actinomycetes showed antifungal activity from soils where P. cinnamomi was causing dieback of jarrah and other understorey species.