Fine Mapping of the Stripe Rust Resistance Gene YrG303 Derived from Wild Emmer Wheat

Stripe rust, caused by the fungus Puccinia striiformis f.s. tritici (Pst), is one of the most destructive diseases of wheat globally. Breeding of resistant varieties is the most sustainable and cost-effective method to control this disease. Depletion of effective resistance to Pst in cultivated wheat has led to search for new genes among wild progenitors of wheat. Recently, we have identified a major dominant gene, designated YrG303, derived from wild emmer wheat, Triticum dicoccoides, which we have mapped to chromosome arm 1BS. The main objective of our project was to clone YrG303 using the positional cloning approach. Fine mapping of YrG303 was achieved based on graphical genotyping of a large hexaploid mapping population produced by composite crosses of the donor T. dicoccoides accession G303, first to bread wheat variety Vaskar and then to Avocet. This mapping population is segregating for a T. dicoccoides chromosome segment carrying YrG303. We have developed a physical map of the YrG303 gene region by anchoring the genetic markers to the physical map of chromosome 1BS constructed by our group (Raats et al. 2013; Genome Biology) and various wheat genomic sequences available in the public databases. The results of high density mapping showed that YrG303 was assigned to the same location as Yr15, derived from T. dicoccoides accession G25. Therefore, we hypothesized that YrG303 is allelic to the well-known dominant gene Yr15, which confers resistance to a broad spectrum of stripe rust races. Further work is under way to validate the function of this gene.