ASEXUAL REPRODUCTION AND BEHAVIOR OF ZOOSPORES OF PHYTOPHTHORA MEGASPERMA VAR. SOJAE

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Abstract
A method was devised to produce abundant zoospores in distilled water suspension from pure cultures of Phytophthora megasperma var. sojae. Sporangia were predominantly non-papillate, but occasionally inconspicuously or conspicuously papillate, germinating with the formation of a delicate, evanescent vesicle. Proliferation of sporangia was observed.Flagella action of freely swimming zoospores was investigated photographically. Both flagella were proved to undulate. Zoospores remained motile longest at 15 °C. Motility was markedly reduced at extreme temperatures (5 and 36 °C), at extreme pH values (below 5.2 or above 9.25), or by mechanical disturbance, dilution, and frequent contact with solid surfaces. The fate of flagella during encystment was followed. Encysted zoospores germinated by germ tubes, or by secondary zoospores, or in rare cases, the germ tube was terminated by a miniature sporangium. Repeated emergence of zoospores was favored at 15 °C whereas total cyst germination and germ tube production was best at 25 °C and in the presence of nutrients.