Genetic And Mapping Of Resistance Gene To Rust In Soybean Germplasm SX6907

Soybean rust（SBR） caused by Phakopsora pachyrhizi, has been reported in most soybean-growing regions, which could result in tremendous yield losses. Compared to the chemical fungicides application, the development of SBR resistance cultivars is the most effective and safe method to control the disease. The SBR resistant germplasms screening and the genetic analysis of resistance genes are the basis to develop SBR resistance cultivars and further mechanism research. Based on the previous screening of resistance germplasm, SX6907 was found to have a highly resistant response to the isolate SS4. To make the full use of SX6907, genetic analysis and gene mapping was carried out in this research. The main results are obtained as follows:1. Genetic analysis of SBR resistance: three F2 populations were constructed by using susceptible cultivars Tianlong1, Zhongdou40 and Pudou11 cross with resistant germplasm SX6907. Rust resistance response was evaluated in parents, F1 and F2 individuals in three populations. All F1 gave red-black lesions, and three types of lesion were observed in F2 individuals. The ratio was 1IM:2RB:1TAN with chi-squared test, indicated that the resistance of SX6907 might be controlled by an incompletely dominant gene.2. Primary mapping of rust resistance gene: Polymorphic markers were screened among parents, resistant and susceptible pool with BSA, and the results showed that the markers on Chromosome18 neighboring the Rpp1 locus were linked to rust resistant gene from SX6907. The analysis of the polymorphic markers in the population of Zhongdou40×SX6907 inferred that the resistant gene was located between BARCSOYSSR₁8₁856 and BARCSOYSSR₁8₁864, within a physical region of 363.9Kb. The same results were also obtained in other two F2 populations from Tianlong1×SX6907 and Pudou11×SX6907.3. Fine mapping of the resistance gene: 11 polymorphic SSR markers were further developed within the primary mapping region. As a result, 16 recombinants were obtained after screening of 800 F2 individuals derived from Tianlong1×SX6907 using flanked two primary mapping markers. Furthermore, the recombinants were analyzed with new markers, combined with their phenotypes, the resistant gene was finely mapped to a region of 111.9Kb,flanking with markers SSR24 and SSR40. Compared to regions and resistant response of the known Rpp1 genes, the resistant gene from SX6907 was thought to be a new locus different from Rpp1, defined as Rpp6907.4. Analysis of the candidate genes: the prediction of genes within the 111.9Kb region showed that 11 high-confidence genes were existed. Among the 11 genes, three genes Glyma18g51930, Glyma18g51950 and Glyma18g51960, belonging to NBS-LRR gene family, were considered to be involved in recognizing the presence of pathogens and conferring resistance.