Molecular mapping of a recessive powdery mildew resistance gene in spelt wheat cultivar Hubel

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most important wheat diseases worldwide. The basis for wheat powdery mildew resistance breeding consists of screening diversified host genetic resources with a range of races of the powdery mildew pathogen. Spelt wheat (Triticum aestivum ssp. spelta 2n = 6x = 42, AABBDD) is a close relative of common wheat (T. aestivum ssp. aestivum) and contains several known disease resistance genes, including Pm1d, Yr5, and Lr65. Here, we report the identification and mapping of a powdery mildew resistance gene in spelt wheat cultivar Hubel, which was introduced to China from Europe and is resistant to Chinese Bgt isolate E09 at the seedling stage. Genetic analysis of a recombinant inbred line population derived from a cross of Hubel and a susceptible early maturing mutant line indicated that Hubel possessed a recessive powdery mildew resistance gene (temporarily designated MlHubel). Markers linked to MlHubel were identified using bulked segregant analysis, simple sequence repeat, and expressed sequence tag-derived sequence tagged site methods. The linked markers were physically located on wheat chromosome 2D. Comparative genomic analysis indicated that the genetic interval covering MlHubel in wheat is highly colinear with the corresponding regions on Brachypodium distachyon chromosome 5 and Oryza sativa chromosome 4. Accordingly, the genetic map of MlHubel was established in comparison with B. distachyon 5L and O. sativa 4L, with the closest marker Xgwm265 being 0.4 cM from MlHubel. The identification of the recessive powdery mildew gene in spelt wheat suggests the potential of this accession along with its closely linked markers in breeding for resistance to powdery mildew.