Studies On Screening For Resistance Source And Genetic Annlysis To P. Sojae In Soybean

Phytophthora root rot (PRR) caused by Phytophthora sojae Kaufmann &. Gerdemann (P. sojae) is a devastating soil-borne dirseases of soybean throughout soybean-growing regions all over the world, such as USA, Brazil, China and so on. There is a increasing trend in China year by year. Phytophthora root rot of soybean has caused tremendous loss in yield and economic in the world. Utilization of resistant varieties is the most economical and environmentally safe method for controlling the disease. The race of P. sojae evolves very fast and the types of physiological races are varied in different regions. Therefore, the rational use of resistant varieties are very important. P. sojae-soybean interaction is a typical model of gene to gene relationship, the resistance genes in soybean can be postulated based on the gene for the gene theory. The major sources of resistance are a series of single dominant host resistance genes (Rps genes). So far, breeding of resistant varieties for complete resistance to P. sojae are the main method in the world.The main goals of this study were:(1) to investigate the distribution and diversity of Phytophthora-resistant soybean and identify new sources of complete resistance resources to P. sojae; (2) to discover genetic mechanism of complete resistance to P. sojae.1. Screen effective resistance sources. (1) 123 soybean cultivars or lines were evaluated for their responses to 10 strains of P. sojae using the hypocotyls inoculation technique.123 cultivars or lines elicited 73 different reaction types with the 10 strains of the P. sojae. Among them 24 reaction types accorded to that of single gene,12 reaction types were consistent with two gene combinations,2 reaction types were consistent with three gene combinations and the others were new reaction types. There were 6 cultivars probably carried gene Rps3b,5 cultivars probably carried gene Rpsld,3 cultivar probably carried gene Rps2c,2 cultivars probably carried gene Rps7,2 cultivars probably carried gene Rps5,1 cultivars probably carried gene Rps3a,1 cultivars probably carried gene Rps4, some cultivars or lines possibly carry new Rps genes that were effective to control Phytophthora root rot of soybean. Among the 123 cultivars, the resistance genes in Jiangsu and Sichuan province were the most abundant, followed by Henan, Beijing and Hubei province. (2) 355 soybean cultivars or lines were evaluated for their responses to 4 isolates (Pm17, Pml9,1020 and Pm8) of P. sojae using the etiolated hypocotyls inoculation technique,355 cultivars or lines elicited 16 different reaction types with the 4 strains of the pathogen.128 of all the resources showed resistance to all the 4 strains accounting for 36.1% of the total identified and 12 were susceptible accounting for 3.4%. The results also showed that there were 22 varieties (lines) may carried Rps7,19 with Rpsld,17 with Rpslc, 6 with Rps3c and 6 with Rps3b,1 with Rpslk.2. Inheritance analysis. There crosses with complete resistance were used to reveal the inheritance of resistance. There were Kefeng36(resistant)×Williams(susceptible), Cangdou5hao(resistant)×Williams(susceptible),Cangdou5hao(resistant)×230598xuan(susce ptible) and the F2:3 population derived from each of the cross were identified the genes for resistance to P. sojae. The results showed that symptom reaction of F1 was identical to that of resistant parent RN-9, the F2 populations segregated in a phenotypic ratio of 3 resistant (R):1 susceptible (S), and the segregation ratio of F2:3 fitted well with the genotypic Mendelian 1 resistant:2 heterozygous:1 susceptible ratio. The complete resistances in Kefeng36 to strain PNJ4 and Cangdou5hao to strain Pm28 were controlled by a single dominant gene (Rps).