Genetic dissection of quantitative powdery mildew resistance loci in tetraploid wheat

Durum wheat, Triticum turgidum ssp. durum Desf., is an important crop particularly in the Mediterranean basin. Powdery mildew, caused by the pathogen Blumeria graminis f. sp. tritici (Bgt), is a major disease of wheat that results in significant yield losses worldwide. A recombinant inbred line (RIL) population, derived from a cross between durum wheat and wild emmer wheat, T. turgidum ssp. dicoccoides, was used for genomic dissection of quantitative and qualitative resistance loci against wheat powdery mildew based on a genomic map of > 600 markers, evenly distributed across the A and B genomes of tetraploid wheat. The genetic analysis of the phenotypic reactions of the RIL population to two Bgt isolates revealed two different resistance mechanisms. The first is monogenic: a wild emmer wheat allele in a single locus conferring complete resistance to Bgt#15, previously designated as PmG16. The second one is polygenic: a set of durum wheat alleles, in five independent QTLs that control partial resistance to Bgt#66 in the RIL population, with a LOD score range of 3.4-19.8. One of them is a major quantitative resistance locus (QRL) that was mapped on chromosome 1A and explains 26.4 % of the variance. In most of the detected QRLs, the durum wheat alleles conferred resistance to powdery mildew. These findings are exceptional in the sense that, so far, only a few Pm alleles originated from a durum wheat background. Therefore, our results emphasize the high potential of exploiting the wide genetic diversity of tetraploid wheat germplasm for wheat breeding using modern wheat genomics tools.