PRECISE MAPPING OF HESSIAN FLY AND STRIPE RUST RESISTANCE LOCI IN PACIFIC NORTHWEST WHEAT GERMPLASM (TRITICUM AESTIVUM L.)

Abstract

Hessian fly and stripe rust are major pests of spring wheat in the Pacific Northwest and cultivar resistance is a primary breeding goal. Hessian fly (HF) infestations continue to cause significant yield losses in spring wheat in the Pacific Northwest. In wheat, resistance to Hessian fly is usually controlled in a gene for gene manner, similar to other pathosystems. Hessian fly resistance genes in wheat have been failing as a result to the rapid evolutionary pace of the insect. Stripe rust (denoted by Yr) is a destructive foliar disease of wheat casing damage on an annual basis. Most of the Yr named resistance genes have been overcome as a result of the continuing emergence of new virulence races. Genetic resistance remains the most effective and economical approach to minimize yield losses and respond to pathogen evolution. A doubled haploid (DH) mapping population was generated from a cross between two elite spring wheat lines; ‘WA8076’, and ‘HT080158LU’. The DH population was genotyped with 90K SNP markers using the Illumina Infinium platform. Phenotypic assessment was carried out on the DH population for both Hessian fly and stripe rust response. The genotyping efforts resulted in a total 15,236 polymorphic SNP markers used to establish a high-density genetic map. A single Hessian fly resistance gene (HFR) derived from ‘WA8076’ was detected on the distal region of chromosome 6BS, flanked by two SNP markers IWB71431 and IWB61175 at a distance of 2.6 cM. In addition, a total of 13 genes/QTL were found to be associated with stripe rust resistance. The adapted superior lines with Yr resistance will be directly incorporated in subsequent breeding efforts as a durable source of resistance. The closely linked SNP markers to the resistance loci, identified in this study, will provide an effective tool to accurately identify, select, and integrate the HF and Yr resistance genes into existing wheat cultivars. The highly dense SNP-based genetic map provides useful information for fine mapping and finding candidate genes underlying QTLs as well as marker-assisted breeding. Furthermore, a genome-wide association study (GWAS) we performed for both seedling and adult plant response in a diverse population of winter wheat germplasm. The population was genotyped with the 90K iSelect wheat single nucleotide polymorphism (SNP) array. Our GWAS study identified a total of 26 loci, comprising a range of existing and novel loci associated with stripe rust resistance. Resistance loci in the winter wheat germplasm can be exploited in the development of broadly-effective disease-resistant commercial wheat cultivars.