Microsatellite markers linked to the Stb2 and Stb3 genes for resistance to septoria tritici blotch in wheat

dSeptoria tritici blotch (STB) of wheat (Triticum aestivum L.), caused by the fungal pathogen Mycosphaerella graminicola (Fuckel) J. Schrdt. in Cohn (anamorph: Septoria tritici Roberge in Desmaz.), occurs naturally in all wheat production areas around the world. Two genes for resistance to this disease, Stb2 and Stb3, have been identified in wheat germplasm and together confer resistance to the most prevalent strains of M. graminicola in Australia and the USA. However, so far neither gene has been mapped in the wheat genome and their linkage relationships to other markers are not known. The objectives of this study were to identify molecular markers linked to the STB resistance genes Stb2 and Stb3 and to map these genes in the wheat genome. Genetic families of doubled-haploid populations segregating for Stb2 and Stb3 were evaluated in the greenhouse for STB reaction during the spring and fall seasons of 2002 and 2003. Genomic DNA isolated from each segregating population was analyzed with microsatellite or simple-sequence repeat (SSR) markers in bulked-segregant analysis to identify those that cosegregated with the STB phenotypes. Linkage analysis identified rive SSR markers near the Stb2 gene on the distal region of the short arm of chromosome 3B. Loci Xgwm389 and Xgwm533.1 were approximately 1 cM distal to Stb2, which itself was 3.7 cM distal to Xgwm493. In addition to Stb2, this genomic region contains multiple genes conferring resistance to taxonomically diverse fungal pathogens of wheat, including a major quantitative trait locus for resistance to Fusarium head blight (caused by Fusarium graminearum Schwabe). The SSR marker Xgdm132 was linked to the Stb3 gene at a distance of approximately 3 cM on the short arm of chromosome 6D. The microsatellite markers identified in this study should facilitate marker-assisted selection and pyramiding of Stb2 and Stb3 with other STB resistance genes for more durably resistant wheat.