Fine Mapping of the Wheat Leaf Rust Resistance Gene Lr2a

Leaf rust (Puccinia triticina) is a major foliar disease of wheat causing economic losses greater than $80 million per year. The exploitation of resistance genes has long been considered the most effective and sustainable method to minimize the losses caused by this disease. The seedling leaf rust resistance gene Lr2a confers effective resistance when paired with the adult plant resistance gene Lr34. The Lr2 locus is an allelic series consisting of the alleles Lr2a, Lr2b, Lr2c, and Lr2d. Previously, Lr2a has been mapped on the chromosome arm 2DS in spring wheat cultivar Superb linked to Kompetitive Allele-Specific PCR (KASP) marker, kwh740. In this study, Lr2a was further fine-mapped in hexaploid wheat using a large F2 population obtained from a cross of the Chinese Spring/RL6016 (Lr2a carrier) to a 1.5 cM genetic interval flanked by markers kwm1618 and kwm1623. The 1.5 cM Lr2a region physically corresponds to a 305.3 kb genomic region on chromosome 2D based on the Chinese Spring reference genome (RefSeqv2.1) and is located on 11.88 Mbp contig in the whole-genome RL6016 assembly. The Lr2a flanking markers kwm1618 and kwm1623 identified 79 recombinant individuals from 2,428 F2 plants. Seventeen new SNP markers generated from RL6016 RNAseq data have been incorporated into a high-resolution genetic linkage map, which placed Lr2a in a 42 kb genomic region on the RL6016 reference assembly. The constructed high-resolution genetic linkage map will facilitate the map-based cloning of Lr2a and its marker-assisted selection. Work is ongoing to clone and further characterize the Lr2a candidate genes.