Fine mapping of the stripe rust resistance gene, YrH52 derived from wild emmer wheat

Stripe rust of wheat, caused by the fungus Puccinia striiformis, is one of the most destructive diseases of wheat. The resistance gene YrH52, derived from wild emmer wheat, Triticum dicoccoides, confers broad spectrum resistance to wheat stripe rust. YrH52 was previously mapped on chromosome 1BS of wheat. The aim of the current study is to refine the genetic map of YrH52 and develop sub-cM map suitable for physical mapping and positional cloning of YrH52. A large mapping population segregating for YrH52 was developed by crossing of a resistant T. dicoccoides accession with a susceptible T. durum cultivar Langdon (LDN). F₂ recombinants were identified by screening of 2600 individuals using YrH52 flanking markers. The flanking markers, XNor1B and Xwmc406 were used as anchors to assign YrH52 to chromosome deletion bin 1BS Sat0.31 on chromosome 1BS. Four CAPS markers were developed based on wheat ESTs mapped to this deletion bin. To further delimit the location of YrH52, we have exploited the synteny between rice, brachypodium, sorghum and wheat. EST-based markers were used to anchor the YrH52 region to the colinear region on brachypodium chromosome 2, rice chromosome 5 and sorghum chromosome 9. Using this comparative genomics approach we were able to refine the genetic map location of YrH52 to 1.3 cM between the closest markers. The flanking markers were used to screen a 1BS BAC library. BAC contigs covering 19.2 Mb were identified in the YrH52 gene region. Further work is underway to complete the physical map and positional cloning of YrH52.