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Techniques

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 28–94% 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.