Identification of a Pm4 Allele as a Powdery Mildew Resistance Gene in Wheat Line Xiaomaomai

Powdery mildew, caused by f. sp. ( ), is one of the most destructive foliar diseases of wheat. In this study, we combined the bulked segregant RNA sequencing (BSR-seq) and comparative genomics analysis to localize the powdery mildew resistance gene in Chinese landrace Xiaomaomai. Genetic analysis of F plants from a crossing of Xiaomaomai × Lumai23 and the derived F population suggests that a single recessive gene, designated as , confers the resistance in this germplasm. A genetic linkage map was constructed using the newly developed SNP markers and was mapped to the distal end of chromosome 2AL. The two flanking markers and were closely linked to at the genetic distance of 3.9 cM and 1.4 cM, respectively. Using the diagnostic primers of , we confirmed that Xiaomaomai carries a allele and the gene function was further validated by the virus-induced gene silencing (VIGS). In addition, we systematically analyzed in comparison with the other alleles. The results suggest that is identical to and at sequence level. is also not different from according to their genome/amino acid sequences. Only a few nucleotide variances were detected between and , which indicate the haplotype variation of the gene.