Cytological mapping of a powdery mildew resistance locus PmRc1 based on wheat-Roegneria ciliaris structural rearrangement library.

Key message: A powdery mildew (Pm) resistance locus PmRc1 was identified and transferred from Roegneria ciliaris into wheat. Two compensative translocation lines carrying PmRc1 were developed. Powdery mildew (Pm), caused by the biotrophic fungal pathogen Blumeria graminis f.sp. tritici (Bgt), is a global destructive disease of bread wheat (Triticum aestivum L.). Identifying and utilizing new Pm resistance gene(s) is the most fundamental work for disease control. Roegneria ciliaris (2n = 4 x= 28, genome S^cS^cY^cY^c) is a wild relative species of cultivated wheat. In this work, we evaluated wheat-R. ciliaris disomic chromosome addition lines for Pm resistance in multiple years. The introduction of R. ciliaris chromosome 1S^c into wheat enhanced resistance. The resistance locus on 1S^c was designated as PmRc1. To cytologically map PmRc1, we induced structural rearrangements using ion irradiation and increasing homoeologous chromosomal recombination. The identified 43 1S^c translocation or deletion lines were used to construct 1S^c cytological bin map by marker analysis using 111 molecular markers. Based on the Pm resistance of the characterized structural rearrangement lines, the PmRc1 locus was cytologically mapped to bin 1S^cS-8 of 1S^c short arm, flanked by markers CMH93-2 and CMH114-1. Two compensatory chromosomal translocation lines (T1S^cS $·$ 1BL and T1S^cS-1AS $·$ 1AL) carrying PmRc1 were developed and assessed for their agronomic traits. Translocation chromosome T1S^cS $·$ 1BL had enhanced Pm resistance accompanied by negative effects on grain number and single plant yield. Translocation chromosome T1S^cS-1AS $·$ 1AL had enhanced Pm resistance and increased spikelet number per spike, without any obvious negative effect on other tested traits. Thus, T1S^cS-1AS $·$ 1AL is recommended preferentially used in wheat breeding for Pm resistance.