Molecular characterization of a new wheat-Thinopyrum ponticum translocation line with resistance to stripe rust

Stripe rust (Puccinia striiformis f. sp. tritici) is a globally devastating foliar disease affecting common wheat. The development of new wheat varieties with novel and durable stripe rust resistance through wide hybridization represents a sustainable and cost-effective strategy for controlling the disease. Thinopyrum ponticum (Podp.) Barkworth & D.R. Dewey, a polyploid species in the tertiary genetic pool of wheat, harbors multiple disease resistance genes, and has been widely utilized for wheat improvement. We previously identified a wheat-Th. ponticum 6J^S (6B) substitution line X005 with novel stripe rust resistance, which was derived from the wheat-Th. ponticum partial amphiploid Xiaoyan7430. In the present study, the chromosome compositions of Xiaoyan7430 and X005 were precisely characterized using non-denaturing - fluorescence in situ hybridization (ND-FISH) and Oligo-FISH painting. Notably, chromosome 6J^S in X005 displayed distinctly different ND-FISH patterns compared to other reported Th. ponticum-derived 6Ae chromosomes introduced into various wheat backgrounds. To physically localize the 6J^S-derived stripe rust resistance gene from X005, we isolated a set of wheat-6J^S deletion and translocation lines after extensive screening of the progenies of crosses between X005 and susceptible wheat cultivars. Using 75 molecular markers, we established a cytological bin map for chromosome 6J^S of X005. Resistance evaluation combined with molecular mapping revealed that the critical resistance locus resides in bin 6J^SS-2 (FL 0.53-0.67) on the 6J^S short arm, corresponding to the 74.51-135.61 Mb genome region of Th. elongatum chromosome 6E. This locus confers stripe rust resistance at both the seedling and adult-plant stages. Translocation T6J^SS·6BL had enhanced Yr resistance and increased tiller numbers without any obvious negative effect on agronomic traits. Thus, the newly developed wheat-Th. ponticum 6J^S translocation lines represent novel germplasm resources for the breeding of disease-resistant wheat cultivars.