Molecular Mapping of YrSP and Its Relationship with Other Genes for Stripe Rust Resistance in Wheat Chromosome 2BL

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is an important disease of wheat worldwide. Resistance is the best way to control the disease. YrSP, a gene originally from ‘Spaldings Prolific’ wheat and providing resistance to a broad spectrum of races, is used for differentiating P. striiformis f. sp. tritici races but its chromosomal location is not clear. To map YrSP, a near-isogenic line (AvSYrSPNIL) was backcrossed to the recurrent parent, Avocet S. Genetic analysis of the BC₇F₁, BC₈, BC₇F₂, and BC₇F₃ progenies confirmed a single dominant gene for resistance. In total, 182 BC₇F₂ plants and their derived BC₇F₃ lines were phenotyped with an avirulent P. striiformis f. sp. tritici race and genotyped with simple-sequence repeat (SSR), single-nucleotide polymorphism (SNP), and sequence-tagged site (STS) markers. A linkage map was constructed with 3 SSR, 17 SNP, and 3 STS markers covering 23.3 centimorgans (cM). Markers IWA638 and dp269 were 0.6 cM proximal and 1.5 cM distal, respectively, to YrSP. The gene was mapped in chromosome bin 2BL-C-0.5, physically within the proximal 50% of the chromosome 2BL arm. Allelism tests based on F₂ phenotypes indicated that YrSP is closely linked to but not allelic with genes Yr5, Yr7, Yr43, Yr44, and Yr53. Infection type data from tests with 10 historical and currently predominant P. striiformis f. sp. tritici races in the United States also demonstrated differences in specificity between YrSP and the other genes. The specificity of YrSP is useful in differentiating P. striiformis f. sp. tritici races and studying the plant–pathogen interactions, and the information of chromosomal location of the gene and its tightly linked markers should be useful in developing resistant cultivars when combined with other genes for resistance to stripe rust.