Fine mapping of PmG3M, a powdery mildew resistance gene derived from wild emmer wheat

Powdery mildew, caused by the parasitic fungus Blumeria graminis f.sp. tritici (Bgt) is one of the most destructive diseases of wheat. Wild emmer wheat (WEW, Triticum turgidum ssp. dicoccoides), the tetraploid progenitor of cultivated wheat, is a valuable source for novel disease resistance genes. PmG3M is a novel dominant gene, derived from WEW, that confers a broad-spectrum resistance to many Bgt isolates from around the globe. PmG3M was genetically mapped on the distal side of chromosome arm 6BL of wheat using segregating mapping populations produced by crossing the resistant WEW accession G305-3M with the susceptible T. turgidum ssp. durum (cv. Langdon). In the current study we saturated the PmG3M gene region with 33 new DNA markers (STSs, EST-SSRs, SSRs, CAPSs and KASPs) developed based on T. aestivum cv. Chinese Spring IWGSC RefSeq assembly v1.0 and WEW Zavitan WEWSeq v.1.0. The PmG3M locus was delimited by two flanking markers that reside 0.18 cM proximal and 0.23 cM distal to PmG3M. Based on the annotated reference genome sequences, several candidate genes were predicted to reside within the target gene region. Microscopic observations revealed a post-haustorial resistance mechanism, since the development of fungal haustoria is blocked at the haustorial bulb stage in the resistant G305-3M. We transferred PmG3M into four Israeli bread wheat cultivars by marker-assisted selection (MAS) and obtained highly resistant BC3F3 lines that can be used for wheat resistance breeding. These studies emphasize the importance of WEW gene pool for improvement of cultivated wheat.