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Physiology and Biochemistry

Stimulation of Sexual Reproduction in the A2 Mating Type of Phytophthora cinnamomi by a Substance in Avocado Roots. G. A. Zentmyer, Professor and plant pathologist, Department of Plant Pathology, University of California, Riverside 92521; Phytopathology 69:1129-1131. Accepted for publication 6 May 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-1129.

Oospore formation was induced in unmated isolates of the A2 mating type of Phytophthora cinnamomi by a substance in an extract or diffusate of avocado (Persea americana) roots. Thus, this heterothallic fungus functioned as a homothallic organism when provided with a specific organic (hormone-like) stimulus. The sexual stage also was initiated by the root extract in A2 mating types of P. capsici and P. drechsleri, but not in A2 types of several other Phytophthora spp. A1 isolates of P. cinnamomi did not produce oospores in the avocado root extract. Similar stimulation was not found in extracts from roots of several other hosts of the pathogen. The stimulatory substance appears to be organic in nature, is nonvolatile, heat-stable, water-soluble, and can be extracted by several organic solvents.