Fine Mapping of Wheat Stripe Rust Resistance Gene Yr26 Based on Collinearity of Wheat with Brachypodium distachyon and Rice

The Yr26 gene, conferring resistance to all currently important races of Puccinia striiformis f. sp. tritici (Pst) in China, was previously mapped to wheat chromosome deletion bin C-1BL-6-0.32 with low-density markers. In this study, collinearity of wheat to Brachypodium distachyon and rice was used to develop markers to saturate the chromosomal region containing the Yr26 locus, and a total of 2,341 F2 plants and 551 F2:3 progenies derived from Avocet S×92R137 were used to develop a fine map of Yr26. Wheat expressed sequence tags (ESTs) located in deletion bin C-1BL-6-0.32 were used to develop sequence tagged site (STS) markers. The EST-STS markers flanking Yr26 were used to identify collinear regions of the rice and B. distachyon genomes. Wheat ESTs with significant similarities in the two collinear regions were selected to develop conserved markers for fine mapping of Yr26. Thirty-one markers were mapped to the Yr26 region, and six of them cosegregated with the resistance gene. Marker orders were highly conserved between rice and B. distachyon, but some rearrangements were observed between rice and wheat. Two flanking markers (CON-4 and CON-12) further narrowed the genomic region containing Yr26 to a 1.92 Mb region in B. distachyon chromosome 3 and a 1.17 Mb region in rice chromosome 10, and two putative resistance gene analogs were identified in the collinear region of B. distachyon. The markers developed in this study provide a potential target site for further map-based cloning of Yr26 and should be useful in marker assisted selection for pyramiding the gene with other resistance genes.