Mining And Identification Of Novel Resistance Gene To Soybean Phytophthora Root Rot

Phytophthora root rot is one of the most important diseases on soybean and cause severe economic losses worldwide. Deployment of resistant or tolerant cultivar is the most effective strategy for controlling this disease. So, it is necessary to consecutively discover and identify novel genes resistance to Phytophthora root rot, which will be great importance for the disease control.1. Screening of resistance resource is a basis of searching for novel resistance genes or QTLs in breeding for disease resistance. In this study, screenings of wild soybean germplasms resistance and tolerance to Phytophthora root rot were performed in order to identify and exploit novel resistant and tolerant sources. One hundred and four wild soybean accessions were used to identified for resistance to two Phytophthora sojae isolates PS41-1(virulence formula: 1a, 1d, 2, 3b, 3c, 4, 5, 6, 7, 8)and PSJS2(virulence formula: 1a, 1b, 1c, 1d, 1k, 2, 3a, 3b, 3c, 4, 5, 6, 7, 8)using cotyledon plug-inoculation method in seedling stage. The result showed that 33 and 35 wild soybean accessions were resistant to isolates PS41-1 and PSJS2, respectively. Moreover, 18 wild soybean accessions were identified resistance to both isolates. Subsequently, 82 wild soybean accessions selected were used for tolerance evaluation to the two P. sojae isolates using inoculum-layer method. The result showed that 7 wild soybean accessions appeared high levels of tolerance. These results indicated that novel sources resistance and/or tolerance to P. sojae were identified in wild soybean germplasms. This study provides valuable material for Phytophthora root rot resistance, which can diversify resistance genetic base of Phytophthora root rot in soybean breeding.2. 232 F2:3 Families derived from a cross of Zaoshu18(resistant) and Williams(susceptible) were used as mapping population. In this study, new SSR makers on the genome region carrying Rps ZS18 were develop and used to finely map Rps ZS18, based on preliminary genetic mapping of the Rps ZS18 on chromosome 2. Further linkage analysis in the F2:3 families revealed that the resistance gene Rps ZS18 was located between SSR makers ZCSSR33 and ZCSSR46 with the genetic distances of 0.9 c M and 0.5c M, respectively. Moreover, the SSR maker Satt172 was co-segregated with the Rps ZS18. The genes existed in the region between ZCSSR33 and ZCSSR46 were surveyed and analyzed. The result showed that the gene model Glyma.02g246000 is the only resistance gene containing the typical Ser/Thr kinase formation, which was supposed as the referenced candidate gene of Rps ZS18. Subsequently, based on the sequence difference in Rps ZS18 locus of contrasting parents, Zasohu18 and Williams, an Indel maker, ZCIndelzs18, was exploited and used to genotyping entire F2:3 population. The further linkage analysis confirmed that ZCIndelzs18 was also a co-segregated maker of Rps ZS18. These two co-segregated makers Satt172 and ZCIndelzs18 can be used in molecular assistant breeding.3. The resistant parent Zaoshu18 harboring Rps ZS18 and 25 related soybean cultivars with a kinship of Zaoshu18 were performed to analyze phenotypic reactions to P. sojae, and haplotypes and polymorphism of referenced candidate gene, Rps ZS18. The phenotypic reactions of the 26 cultivars to 8 P. sojae isolates showed no cultivar appeared the same reaction type to Zaoshu18. Sequences analysis of Rps ZS18 locus showed multiple diversity in this region of the 26 cultivars. And the coding sequence was comparative conserved, which was divided into 13 haplotypes. The developed Indel maker ZCIndelzs18 not only appeared in resistant but also in susceptible cultivars, which means that Indel position of Rps ZS18 is not functional mutation. Interesting, there were particular 8 SNPs and a base insertion occurred in the C-terminal region of Rps ZS18 in Zaoshu18, which was not present in the other applied cultivars. These mutations in C-terminal region of Rps ZS18 in Zaoshu18 can be used to develop a valuable functional marker of Rps ZS18 to accelerate breeding process.