Mapping Quantitative Trait Loci for Slow-Rusting Traits in Wheat

Slow rusting is important for durable resistance to leaf rust in wheat caused by Puccinia truticina and often expressed in the form of long latent period (LP), and low infection type (IT), low area under the disease progress curve (AUDPC), and low final severity (FS). Deployment of slow rusting resistance genes is an effective approach to improve durability of rust resistance. To identify chromosomal regions associated with slow-rusting traits in wheat, we developed a linkage map of 1792 genotyping-by-sequencing SNP (GBS-SNP) markers and 91 SSR markers. Composite interval mapping detected four genomic regions on chromosome 7B, 2B, 3B and 2D associated with slow rusting traits in a recombinant inbred line (RIL) population derived from CI13227 × Suwon 92. Quantitative trait loci (QTLs) for LP, AUDPC, and FS were identified on chromosome 7BL and 2B, IT on 2B in both field and greenhouse experiments, while QTLs for AUDPC and FS on 3B and 2D, LP and IT on 3B were significant in greenhouse experiment only.  The variation (R2) explained by these QTLs ranged from 9.7 to 17.8% for LP, 7.4 to 27.4% for AUDPC, 7.2-15.0% for FS and 7.2-25.3% for IT. Markers Xbarc182 and Xbarc1073 on chromosome 7BL, gwm501 and wmc332 on chromosome 2B, GBS-SNP markers GBSsnp479 and GBSsnp756 on chromosome 3B, GBS-SNP markers GBSsnp1510 and GBSsnp634 [GB1] on chromosome 2D were tightly linked markers for those QTLs. Among these QTLs, the QTLs on chromosomes 7BL and 2B were validated in a different population of double haploids (DHs) derived from CI 13227 × Lakin mapped using 6423 SNPs derived from iSelect 90,000 SNP wheat chip. These SNPs closely linked to the QTLs have been converted to KASP SNP markers and will be used in marker-assisted selection for slow rusting traits from CI13227 in further breeding.