Characterization of Two Adult-Plant Stripe Rust Resistance Genes on Chromosomes 3BS and 4BL in Soft Red Winter Wheat

Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Erikss. (Pst), is an important foliar disease of soft red winter wheat (SRWW) (Triticum aestivum L.) in the eastern United States. However, very few resistance genes have been characterized in the SRWW germplasm pool. The SRWW line VA96W-270 is known to be resistant to stripe rust race PST-100, which was the predominant race in the United States from 2003 to 2006. To elucidate the genetic basis of resistance, a recombinant inbred line (RIL) population developed from a cross between VA96W-270 and the susceptible cultivar Coker 9835 was evaluated for response to stripe rust infection in inoculated field nurseries over a 3-yr period. The RIL population was then genotyped with stripe rust-linked simple sequence repeat (SSR) markers and 90K single-nucleotide polymorphism (SNP) markers. Two major quantitative trait loci (QTL) were identified, located on chromosomes 3BS and 4BL, both contributed by VA96W-270. The 3BS and 4BL QTL explained up to 28 and 25% of the phenotypic variation for area under disease pressure curve (AUDPC), respectively. Recombinant inbred lines containing both QTL had average disease severity of 6%, compared with 38 to 45% for lines containing one of the two QTL and 69% for those containing neither QTL. Based on susceptibility of VA96W-270 to infection at the seedling stage, the two genes appear to be associated with adult-plant resistance. Markers associated with the two QTL were polymorphic in various wheat genotypes, suggesting they could be useful in marker-assisted selection (MAS) to develop wheat cultivars with improved stripe rust resistance.