Germinating Conditions Selection Of Oospores And Development Of Virulent Pure Line Of Phytophthora. Sojae Through Single-Oospore Progeny Segregation

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. The oospores often remain dormant for a period of time to germinate, which comfines the research of inheritance and variation behavior of the oospores. Culture medium, water volume, root exudates of different crops, temperature, illumination affecting germination conditions of oospores of Phytophthora sojae studied in this reasch and compared the difference of germination of oospores of different race of Phytophthora sojae, filtrated the higher germination rate of strain and suitbable conditions combination of germination of oospores; The pure-line(Race 1) in virulence was obtained through isolation and culture and virulence identify of the second generation. The pure-line was analyzed by molecule method of ISSR. The results were summarized as follows:There was quite difference of germination rate of oospores on different culture medium. The oospores of Phytophthora sojae can germinated on water culture medium and did not germinated on CA and S+L culture midium. The germination rate of Phytophthora sojae reached up to 80.9% when the DDW was 3ml. Root exudates of soybean susceptible variety sloan promoted the germination of oospores in evidence. But there is no difference between root exudates of soybean resist variety Suinong 11 , corn variety Benyu 9 and water check.. Whereas there is inhibition to germination of oospores dealed with root exudates of corn variety Benyu 9. The optimum temperature is 26℃ for germination of oospores, the rate of germination reached up to 83.5%. There is no difference among treatments of persistence of dark, alternation between 12 hours dark and 12 hours illumination, continue illumination. The illumination is of no effect on the germination rate of oospores of Phytophthora sojae.30 single-oospore isolates obtained from the test strain of Phytophthora sojae Ps-H2 (Race 1 ) were evaluated using hypocotyl-inoculation method for race phenotype on soybean cultivars. One clone phenotype ( race 1 )was selected randomly for further isolation and virulence identify . The result indicatd that virulence differentiation did not happened in the original strain of Phytophthora sojae, that the original strain of Phytophthora sojae was the pure-line of in virulence of race 1after the second generation .18 pure-line of in virulence of single-oospore isolates of race 1 was carry through DNA fingerprint analysis, cluster analysis showed that most race 1 of P.sojae were the same kind by ISSR with the right primers.