QTL mapping of stem rust resistance in a Bill Brown/Gage winter wheat population

The wheat (Triticum spp.) stem rust pathogen, Puccinia graminis f. sp. tritici Eriks. and E. Henn. (Pgt), has continued to be a devastating biotic stress in wheat production. Over previous decades, scientists have identified several resistance genes effective against Pgt. However, the ever-evolving Pgt and low availability of durable resistance necessitates continuous identification and wise deployment of resistance genes. To elucidate the identity of our previously reported stem rust resistance in hard red winter wheat cultivar Gage, we used recombinant inbred lines (RILs) developed from the cross of Bill Brown × Gage and evaluated them for 3 years for response to six different stem rust pathogen races individually at the seedling stage in the greenhouse and a mixture of these races in the field. Using molecular markers, we determined the genomic regions that affect stem rust resistance in Gage, which identified two quantitative trait loci (QTLs) at the seedling stage and one major QTL at the adult stage, giving insight into why Gage has superior stem rust resistance. The seedling stem rust resistance was from SrTmp and likely from an Sr7 allele. QTLs conferring adult plant resistance in Gage were mainly from Sr2, but molecular analysis suggested additional minor-effect QTLs were involved.