Molecular Mapping of the Stripe Rust Resistance Gene Yr69 on Wheat Chromosome 2AS

Wheat is one of the major food crops in the world. Stripe rust, caused by Puccinia striiformis f. sp. tritici, is an economically important disease that affects wheat worldwide. The discovery of novel resistance genes and the deployment of effectively resistant cultivars are important for the ongoing control of wheat stripe rust and the maintenance of the agricultural productivity of wheat. CH7086, a new stripe rust-resistant wheat introgression line, was selected by crossing susceptible cultivars with the resistant Thinopyrum ponticum-derived partial amphiploid Xiaoyan 7430. The resistance of CH7086 is effective against all current Chinese P. striiformis f. sp. tritici races. CH7086 was crossed with the stripe rust-susceptible cultivars to develop F₁, F₂, F₃, and BC₁ populations for genetic analysis. Segregation in the F₂ and BC₁ populations and F_2:3 lines were tested for resistance against the P. striiformis f. sp. tritici race CYR32. This test showed that CH7086 carries a single dominant gene for stripe rust resistance, which was temporarily designated YrCH86. The closest of the eight simple sequence repeat (SSR) and expressed sequence tag-SSR markers flanking the locus were X2AS33, which is 1.9 cM distal, and Xmag3807, which is 3.1 cM proximal. The resistance gene and its polymorphic markers were placed in deletion bin 2AS-0.78-1.00 using the 'Chinese Spring' nullisomic-tetrasomic, ditelosomic, and deletion lines. The tests of both allelism and resistance specificity suggested that the resistance gene found in CH7086 was not Yr17, which was the only current formally named Yr gene on chromosome 2AS. Thus, YrCH86 appeared to be a new locus and was permanently designated Yr69.