Integrated Genetic Mapping and Transfer of Genes for Ug99 Wheat Stem Rust Resistance from the D Genome of Aegilops tauschii to Bread Wheat, Triticum aestivum

The diploid species Aegilops tauschii contributed the D genome of modern hexaploid wheat, Triticum aestivum, and has provided numerous genes for resistance to fungal pathogens and insect pests. Global wheat production is threatened by the highly virulent Ug99 races of the wheat stem rust fungus, Puccinia graminis f.sp. tritici. Screening a large set of Ae. tauschii germplasm for resistance to TTKSK (Ug99) identified potentially novel sources of resistance that can be transferred to hexaploid wheat. A direct hybridization protocol has been established integrating gene transfer, genetic mapping and introgression into one process. Direct hybridization of Ug99-resistant Ae. tauschii accessions with an elite winter wheat breeding line combines gene transfer and introgression of stem rust resistance genes into a genetic background suitable for breeding. Bulked segregant analysis using individuals from segregating BC₂F₁ populations identifies the chromosome locations of resistance genes facilitating genetic mapping and identification of linked molecular markers. Using this approach, three genes for resistance to TTKSK, located on chromosomes 1DS, 6DS and 7DS have been transferred from Ae. tauschii to T. aestivum and are present in genetic backgrounds suitable for stem rust resistance breeding.