Molecular mapping re-locates the Stb2 gene for resistance to Septoria tritici blotch derived from cultivar Veranopolis on wheat chromosome 1BS

Septoria tritici blotch (STB) is one of the most destructive foliar diseases in many of the wheat (Triticum aestivum) growing regions of the world. Gene Stb2, derived from cultivar ‘Veranopolis’, provides effective resistance against STB. In our attempts to refine the map location of this resistance gene we could not confirm a previous report that Stb2 is on wheat chromosome 3BS. Instead, based on characterization of the same doubled-haploid population used for the original mapping derived from a cross between Veranopolis and susceptible line RAC875-2, and linkage analysis of the resistance phenotype to previously mapped SSR loci, we report that Stb2 is located on the short arm of wheat chromosome 1B, flanked by microsatellite loci Xwmc406 and Xbarc008 (with Xwmc230 closely located) at map distances of 6 and 5 cM, respectively. Presence of the markers on chromosome arm 1BS was confirmed by analysis of nullisomic-tetrasomic lines. These three co-dominant markers can be used in wheat breeding programs to facilitate combining Stb2 with genes of interest. Other STB resistance genes, including Stb11, have been reported on wheat chromosome arm 1BS, with locus Xbarc008 as a diagnostic marker. Whether Stb2, Stb11 and the previously identified Stb11-like genes are the same, allelic, or different but closely linked has not been determined. In addition to STB, numerous genes for resistance to many other fungal pathogens have been reported on wheat chromosome arm 1BS, including those for yellow (or stripe) rust, leaf rust and common bunt. The approximate locations for all of these genes were added onto the Stb2 map based on published distances from common markers to provide a rough guide for future wheat improvement.