Effects of Copper Salts on Growth and Survival of Phytophthora cinnamomi in vitro and on the Antifungal Activity of Actinomycete Populations From the Roots of Eucalyptus marginata and Banksia grandis

Abstract

Seven copper salts and 10 isolates from both mating types of Phytophthora cinnamomi have been tested, in vitro, for copper cation toxicity to mycelial mat growth and to the germination of chlamydospores. It has been shown that while the copper ion is toxic, extended periods of exposure (9-23 days) to the cation are often required to change the fungistatic activity to that of a true fungicide. This observation applies to both mycelial growth and to chlamydospore germination of P. cinnamomi. Soluble copper (CuS0₂.5H₂0) gave short-term protection of both Eucalyptus marginata and to a lesser degree Banksia grandis against infection by P. cinnamomi but insoluble copper (CuO) gave none.

The rhizospheres of seedlings of E. marginata and B. grandis grown in pots contained populations of soil actinomycetes different from each other and the parent soil population. These actinomycetes showed substantial antifungal activity against Phytophthora cinnamomi in vitro. Moreover, the actinomycete populations were modified by the presence of copper and by the infection of the roots by P. cinnamomi. It is suggested that both the actinomycetes and the copper contributed to the protection against invasion by P. cinnamomi.