Abstract
Oospore formation of Phytophthora infestans was induced in potato leaves and stems. Oospores were formed in rare occasions in the leaves, but abundantly in the stems. Oospores were formed only after inoculation with isolates of opposite mating type. The ability of paired isolates to form oospores in host tissues varied among combination of isolates. Oospores were not formed at 10 and 25°C but formed at 15 and 20°C.
