Factors affecting viability of oospores of Phytophthora sojae

Phytophthora root and stem rot, caused by Phytophthora sojae, is a prevalent and destructive disease in some soybean-growing regions. The causal fungus overwinters with oospores in soil and causes soybean root and stem rot next year. Oospores also exist in the diseased seed, but its real significance in the disease cycle is unknown. The oospores often remain dormant for a period of time to germinate, which confines the research of inheritance and variation behavior of the oospores. This study aims at finding a way that can promote germination of oospores in a short time and in a large number. Factors affecting viability of oospores of Phytophthora sojae were evaluated by using tetrazolium bromide. It indicated that oospore age, pretreatment temperature, chemicals can affect to some extent the viability of oospores of P. sojae. Pretreating 45 day-old oospores with KMnO4 at the concentration of 0.4% for 20 min, or with 35 ℃ for five days, favors activies of oospores, and that H2O2, soybean root extract and soybean rhizosphere soil extract have no effect on viability of oospores.