Genetic mapping of a major gene for leaf rust resistance in soft red winter wheat cultivar AGS 2000

Abstract

Leaf rust (LR), caused by Puccinia triticina (Pt), is a major disease of wheat worldwide. Genetic resistance is the most effective, economic, and environmentally safe method to reduce losses caused by LR. Seventy-nine LR resistance genes have been identified so far; however, only a few of them are still effective due to the constant evolution of new Pt races. The objectives of this study were to characterize the genetic basis of LR resistance in the soft red winter wheat (SRWW) cultivar AGS 2000 at seedling stage, and identify markers for marker-assisted selection (MAS). A mapping population of 175 recombinant inbred lines (RILs) was developed from a cross between the susceptible cultivar Pioneer® variety 26R61 (26R61) and AGS 2000. Two out of four Pt races (MBTNB, MFGKG, TCRKG, and MCTNB) showed segregating reactions for the parental lines and RIL population at the seedling stage. Whole genome QTL analysis detected a single common QTL for resistance to both Pt races (MFGKG and MBTNB) on chromosome 2BS. The gene was flanked by wPt-666389 and wPt-2600 markers and explained up to 75.3% of phenotypic variation for Pt race MBTNB, and is therefore a Mendelian factor. LR resistance genes, Lr13, Lr16, Lr23, Lr48, and Lr73, were all detected on 2BS; however, based on their physical and genetic positions, the gene was distinct and therefore temporarily designated as LrA2K. The closely linked marker Xwmc770 to LrA2K has been validated on a set of wheat cultivars and can be used in MAS for LR resistance.