Origin of host-specificity resistance genes of common wheat against non-adapted pathotypes of Pyricularia oryzae inferred from D-genome diversity in synthetic hexaploid wheat lines

Abstract

Wheat resistance genes Rwt3 and Rwt4 constitute a host-specificity barrier against non-wheat pathotypes of the blast fungus, Pyricularia oryzae. To understand the origin of these host-specificity resistance genes, we examined their distribution in Aegilops tauschii, a wild wheat progenitor species with the D genome, using synthetic hexaploid lines derived from crosses between Triticum turgidum cv. Langdon and 54 Ae. tauschii accessions, which cover the native ranges and lineages of the species. Infection assays with transformants carrying their corresponding avirulence genes (PWT3 and PWT4) revealed different distribution patterns of the two resistance genes. Rwt3 was present in the TauL1 and TauL2 lineages with wider geographic distribution, while Rwt4 was mainly present in the TauL2 and TauL3 lineages with narrow geographic distribution. Rwt3 and Rwt4 co-occurred exclusively in a TauL2 sublineage that has been suggested to be a probable donor of the D genome to common wheat. This result suggests that Rwt3 and Rwt4 in common wheat is likely to have been derived from Ae. tauschii individual(s) carrying both genes and that the common ancestor of common wheat had both genes when it was established through amphidiploidization.