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Phytophthora cinnamomi, a Cause of Lethal Disease in Indigenous Plant Communities in Western Australia. F. D. Podger, Forestry Officer, Western Regional Station, Forest Research Institute, Department of National Development, Kelmscott, Western Australia; Phytopathology 62:972-981. Accepted for publication 1 March 1972. DOI: 10.1094/Phyto-62-972.

In southwestern Australia, more than 80,000 hectares of Eucalyptus forest have been destroyed by Phytophthora cinnamomi. Eucalyptus marginata and many other native plants have been killed in forest, woodland, and heath communities. Isolates of the A2 strain of P. cinnamomi were obtained from wildings of 55 species in 34 genera among 15 families. Of 49 isolates tested, 48 were pathogenic to E. marginata seedlings. Each of nine provenances of E. marginata tested was susceptible to a local isolate (I.M.I. 124492) of P. cinnamomi. Typical symptoms developed in healthy forest after the soil was inoculated with pure cultures of P. cinnamomi, and also with soil taken from beneath nearby diseased forest. No symptoms developed after inoculation with soil taken from unaffected forest. Apparently, P. cinnamomi has been introduced recently and is being dispersed with soil moved during road building and logging operations. Thus, the flora of southwestern Australia is being subjected to a new and powerful force of selection which will greatly affect the further evolution of its composition and character. There appear to be no practicable methods of restricting infestations within their present boundaries, although sanitation measures have been applied to reduce the rate of establishment of new centers of infection.

Additional keywords: disease expression climate and seasonal growth, infection on well-drained soils.