Molecular Mapping of Yr85 and Comparison with Other Genes for Resistance to Stripe Rust on Wheat Chromosome 1B

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most serious plant diseases worldwide. Resistant cultivars are the most effective way to control the disease. YrTr1 is an important stripe rust resistance gene that has been used in wheat breeding programs and is represented in the host differential set to identify P. striiformis f. sp. tritici races in the United States. To map YrTr1, AvSYrTr1NIL was backcrossed to its recurrent parent Avocet S (AvS). Seedlings of BC₇F₂, BC₇F₃, and BC₈F₁ populations were tested with YrTr1-avirulent races under controlled conditions, and BC₇F₂ plants were genotyped using simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers. YrTr1 was mapped to the short arm of chromosome 1B using four SSR and seven SNP markers. The genetic distances of YrTr1 from the nearest flanking markers IWA2583 and IWA7480 were 1.8 and 1.3 centimorgans (cM), respectively. DNA amplification of a set of 21 Chinese Spring (CS) nulli-tetrasomic lines and seven CS 1B deletion lines with three SSR markers confirmed the chromosome arm location and further placed the gene in chromosomal bin region 1BS18 (0.5). The gene was determined to be about 7.4 cM proximal to Yr10. Based on multirace response array and chromosomal location, YrTr1 was determined to be different from other permanently named stripe rust resistance genes in chromosome arm 1BS and was named Yr85.