On Physiologic Races Of Phytophthora Sojae And Resistance To The Pathogen In Soybean Germplasm Source

Phytophthora root rot of soybean caused by Phytophthora sojae is one of the most dangerous soybean diseases. The disease was first found in Heilonjiang province of China in 1991 and then the area subject to the disease has continued to expand rapidly. It is forming great potential threat to soybean production of this province. This study served as a basic research for resistance breeding. Physiologic races of isolates were tested, the relationship between virulence variation and DNA polymorphism in the pathogen was studied ,and soybean cultivars/lines from the three Northeast Provinces were evaluated for resistance to Phtophthora sojae. The following are the main results and conclusions of this study:1 Distribution and Physiologic races of the pathogenOn selective media isolates of pathogen was obtained from infected plants originated from Harbin county, Binxian county, Hulan county, Mudanjiang city, Donning county,. Mishan city, Muling county, Jiamusi city, Jixian county of Heilongjiang province and Shulan city of Jilin province. Generally the pathogen distributed widely in Heilongjiang province and geographically centered on the regions around Harbin city, Jiamusi city and Mudanjiang city.By means of hypocotyl inoculation , 42 isolates were tested for physiologic races by using american differintials. Race 1, race 3and race 8 were identified. Race 1 was supposed to be predominant race because it was predominant in number and was found in more regions than other races. It was the first time that race 3 and race 8 was reported in China.American differentials was not suitable to Chinese isolates and we should establish our own differential system for P sojae.Virulence types of the pathogen population in Heilongj iang province was complex and some of the isolates had very strong virulence. The potential threat of the disease should not be neglected. And this also provide an indirect evidence that the pathogen was native , namely not introduced into from abroad.2 The relationship between virulence variation and DNA polyuorphiuD in the pathogenTwenty isolates collected from Heilongjiang province and Jilin province were analyzed for variation in virulence and DNA polymorphism. Virulence characterization was based on the expression of infection types on 8 soybean cultivars/lines used to differentiate races of P. sojae . The inection types were divided into 6 groups. Of 151 RAPD bands that were amplified with 22 random primers and 66. 996 were polymorphic. RAPD analysis showed similarity among the isolates but also difference ,which showed the genetic diversity in the population of P. sojae. Correlation between virulence and RAPD markers was presented in some of isolates of P. sojae.3General evaluation for resistance to Thtcp扟thar3 sojae in soybean cultivars/lines frau the three Northeast ProvincesFor the first time resistance to Phtophtbora sojae in soybean cultivars /lines from the three Northeast Provinces of China was evaluated systematically. The result showed that 7.6% of the tested cultivars limes were resistant to theU.S. 梠riginated R25 with strong virulence, 28. 3% were resistant to the native H4 (race I) and 2. 6% were resistant to both R25 and 1-14, which meaned that the resistance germplasm in soybean was very rich in the three Northeast provomces. Cultivars /lines Xin 3709, Shengnong 9144, Dan 87??1?05, Dan 87?, Dan 87??1?06 were resistant to all the eight tested isolates, which meaned that they carried multi梤esistance genes and had high value in resistance breeding. The resistance genes in some cultivars/iines were postulated and the result showed that Fuyuandali, Dongnong 92?033, Suinongl5, Sui 95?672, Suinong 8,Nongda 5956 and 85?2(Heidou) carried Rpsl梐 and Rps7, however might have additional resistance genes.Ph.D Candidate: Xu XiuhongLiar: Crop Genetics and BreedingSupervisor:Prof. Wang JinlingProf. Yang QingkaiProf. Zhang Guodong...