Identification of Stripe Rust Resistance Loci in US Spring Wheat Cultivars and Breeding Lines Using Genome-Wide Association Mapping and Yr Gene Markers

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), poses a major threat to wheat production worldwide, especially in the United States. To identify loci for effective stripe rust resistance in U.S. wheat, a genomewide association study (GWAS) was conducted using a panel of 616 spring wheat cultivars and breeding lines. The accessions in this panel were phenotyped for stripe rust response in the greenhouse at seedling stage with five predominant and highly virulent races of Pst and in different field environments at adult-plant stage in 2017 and 2018. In total, 2,029 single-nucleotide polymorphism markers that cover the whole genome were generated with genotyping by multiplexed sequencing and used in GWAS. In addition, 23 markers of previously reported resistance genes or quantitative trait loci (QTLs) were used to genotype the population. This spring panel was grouped into three subpopulations based on principal component analysis. A total of 37 genes or QTLs including 10 potentially new QTLs for resistance to stripe rust were detected by GWAS and linked marker tests. The frequencies of the resistance genes or QTLs in various nurseries were determined, indicating different intensities of these genes or QTLs used in breeding programs of different regions. These resistance loci and the information on their markers, effectiveness, and distributions should be useful for improving stripe rust resistance in wheat cultivars.