Molecular Markers Of Yellow Rust Resistance Genes In Wheat

Yellow rust (Puccinia striiformis Westend f. sp. tritici) is one of the most important wheat diseases worldwide. Breeding for resistance is considered the most economical and effective way for controlling the disease. Molecular markers for yellow rust resistance genes have developed in the past years and have facilitated the marker assisted selection of the resistance genes in wheat breeding program. Among the molecular marker techniques used for disease resistance gene mapping, microsatellite marker has such advantages as efficiency, stability, codominance, abundance and distribution throughout the genome. In this thesis, two yellow rust resistance genes, derived from S2199 and G90-21, were mapped with SSR markers by applying a bulked segregant analysis (BSA). The results obtained are as follows:1. Genetic analysis of yellow rust resistance indicated that a single dominant gene was responsible for the yellow rust resistance in common wheat line S2199, a very sound resistance resource against the prevailing yellow rust isolates in China. SSR markers Xdp269 and Xgwml20 were found to be linked to the resistance gene, with genetic distance of OcM and 5.96cM, respectively. SSR marker Xgwml20 has been mapped on 2BL chromosome arm and Xdp269 is located on 2BL too after performing BLAST search and comparative genomics analysis. Since Xdp269 was found to be co-segregated with the yellow rust resistance gene in a more than 400 plants population, in silico chromosome walking in the rice chromosome 4 was performed and the results indicated that a disease resistance gene cluster was physically located 3 BACs away from the DP269 corresponding EST. Therefore, Xdp269 may be used as a starting point for in silico chromosome walking and towarding the yellow rust resistance gene. Possible relationship between Yr5 and the resistance gene from S2199 was also discussed.2. Genetic analysis of yellow rust disease resistance indicated that a single dominant gene control the yellow rust resistance in G90-21, a yellow rust resistance line from former Gui Zhou Agricultural College. SSR analysis in a segregating population derived from (G90-21/704)F₂/温 8 indicated that three SSRs: Xbarc240, Xbarcl87 and Xgwm413, could generate polymorphic DNA fragments between the resistant and susceptible plants. The genetic distance between the resistance gene and the three SSR markers Xbarc240, Xbarcl87 and Xgwm413 were 4.0cM, 6.2cM and 7.3cM, respectively. All the three SSRs were located in chromosome 1B and since Xgwm413 was found to be linked to Yr26 and G90-21 has the same resistance resource, T. turgidum, with Yr26, the yellow rust resistance gene from G90-21 might be also the Yr26 gene.