Homoeologous recombination-based transfer and cytological mapping of the novel powdery mildew resistance gene Pm7C from Aegilops caudata.

Key message: A novel powdery mildew resistance gene Pm7C from Aegilops caudata was introgressed into common wheat through ph1b-induced homoeologous recombination and mapped to the 7CL bin FL 0.90-0.96 on chromosome 7C. Wheat powdery mildew poses a significant threat to wheat grain yield and quality. Developing resistant wheat varieties through the deployment of resistance genes is the most effective, economically feasible, and environmentally sustainable strategy to combat this disease. Aegilops caudata (2n = 2x = 14, CC), a wild relative of common wheat, has been identified as a valuable genetic resource harboring novel resistance loci. Specifically, chromosome 7C of Ae. caudata carries a novel broad-spectrum resistance gene, tentatively designated as Pm7C. However, the structural variations in chromosome 7C, coupled with the unavailability of a reference genome for Ae. caudata, have hindered the introgression of this resistance gene into common wheat and its mapping. In this study, we report the development of wheat-Ae. caudata 7C recombinants via ph1b-induced homoeologous recombination and the cytological mapping of the resistance gene Pm7C. By integrating the analysis of 69 7C-specific markers with breakpoint mapping of 7C recombinants using in situ hybridization, we characterized 35 wheat-Ae. caudata 7C recombinants, categorizing them into 10 distinct types. This enabled the construction of a physical map of 7C, comprising nine chromosomal bins defined by 69 specific markers. Subsequent evaluation of powdery mildew resistance in these recombinants mapped Pm7C to the long arm of 7C within the interval of FL 0.90-0.96. Additionally, terminal recombinant 7CT1 (T7DL.7DS-7CL) and intercalary recombinant 7CT4 (Ti7DL.7DS-7CL-7DS) were identified as containing small 7CL segments that harbor Pm7C. These resources are expected to facilitate wheat disease-resistant breeding and further efforts in cloning and elucidating the resistance mechanism of Pm7C.