Genetic mapping of the wheat leaf rust resistance gene Lr19 and development of translocation lines to break the linkage with PSY-E1

Abstract The Lr19 locus, which was transferred to wheat from the wheat relative Thinopyrum ponticum in 1966, still confers broad resistance to most known leaf rust isolates worldwide. However, this gene has not been fine mapped to day, and its tight linkage with the yellow pigment gene PSY-E1 has limited the deployment of Lr19 in bread wheat breeding. In this paper, we genetically mapped Lr19 using a bi-parental population obtained by crossing two wheat- Th. ponticum substitution lines, 7E1(7D) (carrying Lr19 ) and 7E2(7D) (susceptible to leaf rust). Genetic analysis of the F 2 population and F 2:3 families showed that Lr19 is a single dominant gene, and it was successfully mapped within a 0.3 cM interval on the long arm of the Th. ponticum chromosome 7E1, flanked by markers XsdauK3734 and XsdauK2839 . To reduce the size of the Th. ponticum chromosome segment carrying Lr19 , the Chinese Spring Ph1b mutant was employed to promote recombination between the homoeologous chromosomes of the wheat chromosome 7D and 7E1. Two translocation lines with short Th. ponticum chromosome fragments carrying Lr19 were identified using markers closely linked to Lr19 , and in one of the lines the linkage between Lr19 and PSY-E1 was broken. Both translocation lines were resistant to 16 Pt isolates collected from China. Thus, the Lr19 linkage markers and translocation lines developed in this study can be used for marker-assisted selection in common wheat breeding programs.