Effects of light on oospore germination of Aphanomyces euteiches

The effect of light on oospore germination of Aphanomyces euteiches was investigated. Of 29 isolates, from 5 districts in Japan, 7 were obviously promoted oospore germination by light exposure. Two isolates AE-F10 and AE-M3a were studied in detail. More than 90% of isolate AE-F10 oospores germinated with 10 days of 2, 000lux white fluorescent light exposure at 28C. About 20% of isolate AE-F10 oospores germinated with the exposure to 50lux light for 15 days. Oospore germination of isolate AE-M3a was not promoted by light exposure. Light exposure under low temperature also promoted isolate AE-F10 oospore germination and about 50% of oospores germinated with light exposure for 10 days at 5C. Light exposure to oospores born in culture which was younger than 30 days did not promote germination. Oospores of both isolates germinated only low proportion by the aging of 10 to 150 days on water agar.