Identification and validation of a functional allele of the powdery mildew resistance gene Pm68 derived from the wild emmer wheat introgression line R53M

Powdery mildew caused by the fungus Blumeria graminis f. sp. tritici ( Bgt ) is a prevalent disease that restricts wheat ( Triticum aestivum ) production globally. Diverse Bgt resistance genes and alleles are continually needed for wheat disease resistance breeding. We identified a wild emmer wheat ( Triticum dicoccoides , WEW) introgression line, R53M, with effective resistance to Bgt isolate E09 starting at the two-leaf stage, during powdery mildew resistance assays in the greenhouse. Genetic analysis indicated that R53M carries a dominant powdery mildew ( Pm ) resistance gene, designated as PmR53M . We mapped PmR53M to the short arm of chromosome 2B, at the same approximate location as the resistance loci Pm68 / MlIW39 / PmWR183 from WEW. Sequence analysis revealed that the genetic interval containing the PmR53M locus includes Pm68d , an allelic variant of Pm68 . We confirmed the resistance conferred by the PmR53M / Pm68d using virus-induced gene silencing (VIGS) and transgenic assays. This resistance results from the combined effect of two complementary nucleotide-binding and leucine-rich repeat (NLR) genes. In contrast to the all-stage resistance observed with Pm68 and MlIW39 , PmR53M only conferred complete resistance to powdery mildew starting at the two-leaf stage, similar to PmWR183 , which provides resistance at the three- and four-leaf stages. We developed co-segregating gene-based markers for the identification of PmR53M . The discovery of PmR53M enriches the Pm gene pool in wheat and should facilitate the genetic improvement of powdery mildew resistance