Effects of cellulytic enzymes on Phytophthora cinnamomi

Two enzyme systems, cellulase (beta -1,4-glucanase) and Iaminarinase (beta -1,3-glucanase), were added to soil extracts to simulate (in vitro) lytic c omponents found in mulches suppressive to Phytophthora cinnamomi. Concentra tion ranges of each enzyme were incubated with Phytophthora cinnamomi mycel ium, zoospores, zoospores cysts, and zoospore-infected excised roots to eva luate the roles of each enzyme in potential control of avocado root rot dis ease. Cellulase significantly retarded the development of zoosporangia and chlamydospores when mycelia were incubated in soil extract containing the e nzyme at concentrations greater than 10 units/ml. Zoospore production was a lso reduced by cellulase but not by laminarinase. Laminarinase had little e ffect on zoosporangia or chlamydospore formation. At high concentrations, l aminarinase was consistently more effective at preventing encystment than c ellulase. Chlamydospores preformed in root tips were immune to the lytic ef fects of all treatments except cellulase at 100 units/ml. Zoospores placed in enzyme solutions and plated on a selective medium survived high cellulas e concentrations and formed colonies, but there were fewer surviving zoospo res when laminarinase was present at greater than 10 units/ml. Low concentr ations of cellulase stimulated infection of excised roots, however, low con centrations of laminarinase prevented infection. Cellulase and laminarinase have different effects on the structures of the Phytophthora cinnamomi lif e history, however, each enzyme may have a role in reduction of inoculum.