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Induction of Oospore Germination of Phytophthora parasitica. P. J. Ann, Graduate research assistant, Department of Plant Pathology, University of Hawaii, Beaumont Agricultural Research Center, Hilo 96720, Present address: Chia-yi Agricultural Experiment Station, Chia-yi, Taiwan; W. H. Ko, Professor, Department of Plant Pathology, University of Hawaii, Beaumont Agricultural Research Center, Hilo 96720. Phytopathology 78:335-338. Accepted for publication 12 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-335.

Oospores from the cross between A1 and A2 mating types of Phytophthora parasitica were exposed to light during maturation, treated with 0.25% KMnO4 for 20 min, and incubated at 24 C under light on a medium consisting of glucose, lecithin, and Bacto agar (S + L medium). Under such conditions, germination of oospores from 60-day-old culture commenced within 24 hr and reached more than 90% after 10 days. Treatment with KMnO4 also prevented the germination of residual mycelial fragments, chlamydospores, and sporangia present in the oospore suspension. Germination rate of oospores increased with age of culture, reaching more than 90% at the age of 56 days. Germination of oospores decreased from 95 to 44% when light was omitted during maturation of oospores, and to 15% when light was omitted during germination. Oospores did not germinate when light was not provided during maturation and germination. Oospores did not germinate in distilled water, but 2894% did germinate on nutrient media. Among the media tested. S + L medium was the best, followed by V-8 agar and water agar. All the concentrations of KMnO4 tested ranging from 0.05 to 1.0% were effective in inducing oospore germination. Treating oospores with 0.25% KMnO4 for more than 20 min appeared to be harmful to oospores. Germination of oospores was completely inhibited when oospores were exposed to 15 C for 24 hr before or after treatment with KMnO4.