Characterization of Pm72, a new powdery mildew resistance gene on chromosome 6AL of Triticum boeoticum accession PI 427741

Triticum monococcum ssp. aegilopoides (syn. T. boeoticum) is a wild diploid species that harbors the A^bA^b genome containing many disease resistance genes useful for wheat improvement. Genetic analysis conducted on an F₂ population from a cross between T. boeoticum accessions PI 427741 and PI 427560, which are contrasting in powdery mildew responses, indicated that the resistance in PI 427741 was controlled by two dominant genes, PmNCA6 and another unknown gene. Bulked segregant exome capture sequencing (BSE-Seq) analysis of a segregating F₃ family without PmNCA6 demonstrated a new powdery mildew resistance gene, Pm72, on the long arm of chromosome 6A. Through linkage analysis, Pm72 was mapped to a 1.28-cM genetic interval defined by markers XTb6AL04 and XTb6AL06. According to the reference genome of T. boeoticum accession TA299, the Pm72 locus corresponded to a 940-kb physical region (Chr6A: 635,963,867–636,888,696), containing 21 nucleotide-binding leucine-rich repeat receptor (NLR)-like disease resistance genes. Phenotyping showed that Pm72 confers effective resistance to powdery mildew at both the seedling and the adult-plant stages in the hexaploid wheat background. The co-segregating marker XTb6AL05 was useful for marker-assisted selection of Pm72. The identification of the new powdery mildew resistance gene Pm72 will contribute to its positional cloning and breeding application in wheat.