Abstract
Oospores of downy mildew fungus, Peronospora manshurica, of soybean, Glycine max, were well formed when the lesions were immersed in water or under humid condition. Oospores were not formed when the lesions were submerged in water or kept under dry condition. In the immersion treatment at 5 C neither oogonium nor oospore was formed and at 25C only a few oogonia were formed. At 10 C oogonia and oospores were formed, but in small number. At 15 and 20 C abundant oogonia and oospores were formed. At 15 C oogonia were abundantly formed after 3 day-immersion and reached the maximum number after 4 day-immersion. Oospores developed after 2 days following oogonium formation. At 20 C oogonia were formed after 3 day-immersion and reached the maximum number after 4 day-immersion, as well at 15 C. Oospore development at 20 C was, however, 1 day earlier than that at 15 C. Size of oogonium thus obtained was 36.0×40.2 μm, and that of oospore was 27.6 μm in diameter on the average.
