Fine mapping of the stripe rust resistance gene Yr85 in wheat

Breeding resistant wheat (Triticum aestivum) cultivars is the most efficient way to manage wheat stripe rust, a highly destructive disease caused by the fungal pathogen Puccinia striiformis f. sp. tritici (Pst). Therefore, the exploration of new resistance genes is ongoing. The resistance gene Yr85 confers protection against predominant Pst races in China at all stages of plant development. Here, we fine-mapped Yr85 to a 0.12 cM interval between allele-specific quantitative PCR markers XK1B-61 and XK1B-65, corresponding to a 1.76 Mb region on chromosome 1BS in the IWGSC RefSeq v2.1 reference genome (wheat cultivar Chinese Spring), using 5507 F₅ plants derived from heterozygous F₄ plants, themselves descendants of an AvS × AvSYr85NIL cross. Haplotype analysis and whole-genome resequencing suggested that Yr85 may be from a distant source. Moreover, agronomic trait evaluation indicated that Yr85 is located in a chromosomal region lacking linkage drag. Genotyping of 309 Chinese wheat cultivars and lines with a marker that cosegregated with Yr85 during fine mapping identified one cultivar possibly carrying the resistance gene. Our findings indicate that Yr85 has potential for use in wheat-breeding programs in China. This study lays the foundation for map-based cloning and marker-assisted selection of Yr85.