Discovery of the New Leaf Rust Resistance Gene in Wheat: Molecular Mapping and Marker Development.

Breeding for leaf rust resistance has been successful worldwide and is underpinned by the discovery and characterisation of genetically diverse sources of resistance. An English scientist, Arthur Watkins, collected pre-Green Revolution wheat genotypes from 33 locations worldwide in the early part of the 20th Century and this collection is now referred to as the 'Watkins Collection'. A common wheat genotype, Aus27352 from Yugoslavia, showed resistance to currently predominating Australian pathotypes of the wheat leaf rust pathogen. We crossed Aus27352 with a leaf rust susceptible wheat selection Avocet S and a recombinant inbred line (RIL) F population of 200 lines was generated. Initial screening at F generation showed monogenic segregation for seedling response to leaf rust in Aus27352. These results were confirmed by screening the Aus27352/Avocet S RIL population. The underlying locus was temporarily named . Bulked segregant analysis using the 90K Infinium SNP array located in the long arm of chromosome 2B. Tests with molecular markers linked to two leaf rust resistance genes, and , previously located in chromosome 2B, indicated the uniqueness of and it was formally designated . Kompetitive allele-specific polymerase chain reaction assays were developed for -linked SNPs. mapped 0.8 cM proximal to and was placed 1.2 cM distal to this locus. showed 91% polymorphism among a set of 89 Australian wheat cultivars. We recommend the use of for marker assisted pyramiding of in breeding programs following polymorphism check on parents.