High-density mapping of a resistance gene to Ug99 from the Iranian landrace PI 626573
Managing wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is imperative for the preservation of global food security. The most effective strategy is pyramiding several resistance genes into adapted wheat cultivars. A search for new resistance sources to Pgt race TTKSK resistance identified a spring wheat landrace, accession PI 626573, as a potentially novel source of resistance. A cross was made between LMPG-6, a susceptible spring wheat line, and PI 626573 and used to develop a recombinant inbred population to map the resistance. Bulk segregant analysis (BSA) of LMPG-6/PI 626573 F2 progeny determined resistance was conferred by a single dominant gene given the provisional designation SrWLR. The BSA identified nine microsatellite (SSR) markers on the long arm of chromosome 2B associated with the resistant phenotype. Fifteen polymorphic SSRs, including the nine identified in the BSA, were used to produce a linkage map of chromosome 2B, positioning SrWLR in an 8.8 cM region between the SSRs GWM47 and WMC332. This region has been reported to contain the wheat stem rust resistance genes Sr9 and SrWeb, the latter conferring resistance to Pgt race TTKSK. The 9,000 marker Illumina Infinium iSelect SNP assay was used to further saturate the SrWLR region. The cosegregating SNP markers IWA6121, IWA6122, IWA7620, IWA8295, and IWA8362 further delimited the SrWLR region distally to a 1.9 cM region. The present study demonstrates the iSelect assay to be an efficient tool to delimit the region of a mapping population and establish syntenic relationships between closely related species.