Studies On Population-Genetic Structure And Pathogenicity-Related Genes In Phytophthora Sojae

Phytophthora sojae is a major challenge to the production of soybean in the world. Plant resistance is currently the major control method for P. sojae root rot on soybean. However, resistant cultivars can promote the buildup of new virulent populations. Naturally virulent populations have been recovered from cultivated fields and natural areas; these infestations have resulted in the failure of resistant soybean cultivars. Therefore, genetic diversity in P. sojae population was studied to facilitate the soybean breeding for durable resistance and the disease integrated management. Moreover, studies on the pathogenicity mechanisms of oomycetes including P. sojae will help us to find special molecular targets of controlling the oomycete diseases.A simple and effective method to isolate P. sojae from soils was established. Penicillin, rifampicin, quintozene and carbendazim were used on the stages of oospore germination and zoospore baited by soybean leaf discs in the isolation of P. sojae from soil. These chemicals can most effectively eliminate Pythium and baterial contamination, and the pure isolates of P. sojae can be easily obtained. Under the control of chemical, the rate of baiting p. sojae from soils contained 100 oospores was 100%. Using this method, P. sojae was baited from soils collected from Heilongjiang province, soybeans imported from both Brazil and USA. The results showed that the rate of baiting p. sojae in soil samples from Heilongjiang province was 53%, and in soil samples collected from soybeans imported was 73%.The genetic diversity of three geographic populations of P. sojae from China and USA was determined using simple sequence repeats (SSRs) and random amplified polymorphic DNA (RAPD). Twenty pairs of SSR primers amplified 113 bands (alleles), of which all bands were polymorphic. Twenty-one of totally 200 random primers were selected were screened. A total of 223 reproducible RAPD fragments were scored among 111 individuals, of which 199 (89.23%) were polymorphic. Genetic similarity analysis based on SSR and RAPD fingerprints showed that the P. sojae populations of Fujian province and the United States were more similar to each other than to populations from Heilongjiang province. Cluster analysis with the unweighted pair group method revealed that the 111 isolates of P.