A Comparison of Phytophthora cinnamomi Infection in Eucalyptus sieberi, a Susceptible Species, and Eucalyptus maculata a Field Resistant Species

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Abstract
Zoospores of Phytophthora cinnamomi Rands were attracted, in almost equal numbers, to seedling roots of Eucalyptus sieberi (a susceptible species) and Eucalyptus maculata (a field resistant species). Germinating zoospores penetrated and mycelium developed within seedling roots of both species. The root and shoot growth of both eucalypt species were reduced by P. cinnamomi infection. In E. sieberi the growth reduction was greater than in E. maculata seedlings and other symptoms of infection were evident. Cell-free extracts of P. cinnamomi were able to produce some of the symptoms of infection in the absence of parasitism. Root growth of both eucalypt species was reduced at high extract dilutions and seedling deaths occurred at low extract dilutions.