Fine mapping of a powdery mildew resistance gene MlIW39 derived from wild emmer wheat (Triticum turgidum ssp. dicoccoides)

Key message Powdery mildew resistance gene MlIW39, originated from wild emmer wheat accession IW39, was mapped to a 460.3 kb genomic interval on wheat chromosome arm 2BS. Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is destructive disease and a significant threat to wheat production globally. The most effective way to control this disease is genetic resistance. However, when resistance genes become widely deployed in agriculture, their effectiveness is compromised by virulent variants that were previously minor components of the pathogen population or that arise from mutation. This necessitates continual search for new sources of resistance in both wheat and its near relatives. In this study, we produced a common wheat line 8D49 (87-1/IW39//2*87-1), which has all-stage immunity to Bgt isolate E09 and many other Chinese Bgt isolates, by transferring powdery mildew resistance from Israeli wild emmer wheat (WEW) accession IW39 to the susceptible common wheat line 87-1. Genetic analysis indicated that the powdery mildew resistance in 8D49 was controlled by a single dominant gene, temporarily designated MlIW39. Genetic linkage analyses with molecular markers showed that MlIW39 was located in a 0.7 cm genetic region between markers QB-3-16 and 7Seq546 on the short arm of chromosome 2B. Fine mapping using three large F-2 populations delimited MlIW39 to a physical interval of approximately 460.3 kb region in the WEW reference genome (Zavitan v1.0) that contained six annotated protein-coding genes, four of which had gene structures similar to known disease resistance genes. This provides a foundation for map-based cloning of MlIW39. Markers 7Seq622 and 7Seq727 co-segregating with MlIW39 can be utilized for marker-assisted selection in further genetic studies and wheat breeding.

Automated summary

In this study, the powdery mildew resistance gene MlIW39 was transferred from Israeli wild emmer wheat accession IW39 to a susceptible common wheat line 87-1, resulting in the development of a powdery mildew-resistant common wheat line 8D49. Genetic analysis showed that the resistance in 8D49 was controlled by a single dominant gene, MlIW39, located on chromosome 2B in a 460.3 kb genomic interval. Fine mapping and annotation of neighboring genes provided a foundation for map-based cloning of MlIW39, with potential marker-assisted selection using co-segregating markers 7Seq622 and 7Seq727.