Powdery mildew disease resistance and marker-assisted screening at the Pm60 locus in wild diploid wheat Triticum urartu

Triticum urartu, a diploid wild wheat and progenitor of the A genome of bread wheat, is an important resource for resistance to powdery mildew fungus caused by Blumeria graminis f. sp. tritici (Bgt). In the present study we systematically characterized the interaction between the Bgt fungus and T. urartu at the microscopic level. We also tested 227 T. urartu accessions for reaction to Bgt isolate E09 and discovered previously uncategorized powdery mildew resistance in this collection. Pm60 is a CC-NB-LRR type powdery mildew resistance gene that has at least three functional alleles, Pm60, Pm60a, and Pm60b. A marker-assisted screen targeting the Pm60 locus identified a non-functional allele of Pm60a, designated as Pm60a′. A sequence comparison of Pm60a′ and Pm60a revealed that they differed by 58 SNPs and one 3-nucleotide deletion. Based on the sequence variations two molecular markers were developed to differentiate the functional Pm60a allele from the non-functional Pm60a′. Our screen revealed the presence of a previously uncharacterized powdery mildew resistance in T. urartu and provides new insights into the Pm60 locus. We believe that the two molecular markers developed here and new T. urartu resistant accessions will facilitate further identification of novel powdery mildew resistance genes and benefit breeding for powdery mildew resistance.