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An interspecific barberry hybrid enables genetic dissection of non-host resistance to the wheat stem rust pathogen

Radhika Bartaula: University of New Hampshire

<div>Stem rust, caused by <em>Puccinia graminis </em>(<em>Pg</em>), is one of the most destructive diseases of wheat worldwide; and the threat of <em>Pg</em> to global food security is enhanced by its ability to rapidly evolve new forms of virulence. The emergence of the highly virulent wheat stem rust races, most notably the <em>Ug99</em> family of stem rust races radiating out of East Africa, underscores the need for durable mechanisms of genetic resistance to <em>Pg</em>. Due to its intrinsic durability, non-host resistance (NHR) presents a compelling vision; but NHR to <em>Pg</em> remains largely unexplored as a protection strategy in wheat, in part due to the challenge of developing a genetically tractable system in which <em>Pg</em>-NHR segregates. In this study, we approached the question of <em>Pg</em>-NHR through the pathogen's sexual host, barberry (<em>Berberis</em> spp.). Using an interspecific mapping population derived from a cross between <em>Pg</em>-susceptible <em>B. vulgaris</em> and <em>Pg</em>-resistant <em>B</em>. <em>thunbergii</em>, we have begun to dissect the genetics of the <em>Pg</em>-NHR exhibited by <em>B</em>. <em>thunbergii</em>. Building on our 1.3 Gb genome for <em>B</em>. <em>thunbergii </em>and genetic linkage maps for both parental species, QTL analysis identified a single QTL for <em>Pg</em>-NHR, spanning ~7 cM (~1.74 Mbp; LOD = 33.16). Candidate genes are prioritized for follow-up study based on both differential expression under <em>Pg</em> challenge and function-related <em>Bv</em>-<em>Bt</em> sequence variation. With this study, we demonstrate for the first time the feasibility of dissecting the genetics of a source of <em>Pg</em>-NHR, which may contribute insight into possible novel mechanisms of durable rust resistance in wheat.</div>

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