Germination of Oospores Produced by Phytophthora Megasperma Var. Sojae

SUMMARY

Thick-walled oospores of the homothallic Phytophthora megasperma var. sojae contained a large refractile body and two smaller pellucid bodies which prior to germination appeared to be absorbed. When oospores in V-8 juice agar were subjected to 2 hr per day of fluorescent light, frozen for 24 hr to kill the mycelium, and incubated in water, about 40–70% germinated. The inner surface of the thick oospore wall appeared to erode from the inside just prior to germination. Incubation of cultures at 24 and 27 C was much more favorable for germinability of oospores than 15, 18 or 30 C. Although mycelial growth was excellent at 30 C, most oospores were malformed. No variation in morphology, cultural growth or pathogenicity among 23 single-oospore cultures was detected.