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.