Introgression of / Into Barley Germplasm Provides Insights Into the Genetics of Resistance to f. sp. Race TTKSK and Resources for Developing Resistant Cultivars.

Stem rust (incited by f. sp. ) is a devastating disease of wheat and barley in many production areas. The widely virulent African f. sp. race TTKSK is of particular concern, because most cultivars are susceptible. To prepare for the possible arrival of race TTKSK in North America, we crossed a range of barley germplasm-representing different growth habits and end uses-with donors of stem rust resistance genes and . The former confers resistance to prevalent races of f. sp. in North America, and the latter confers resistance to TTKSK and other closely related races from Africa. We produced doubled haploids from these crosses and determined their allele type at the loci and haplotype at 7,864 single-nucleotide polymorphism loci. The doubled haploids were phenotyped for TTKSK resistance at the seedling stage. Integration of genotype and phenotype data revealed that (i) was not associated with TTKSK resistance, (ii) was necessary but was not sufficient for resistance, and (iii) specific haplotypes at two quantitative trait loci were required for to confer resistance to TTKSK. To confirm whether lines found resistant to TTKSK at the seedling resistance were also resistant at the adult plant stage, a subset of doubled haploids was evaluated in Kenya. Additionally, adult plant resistance to leaf rust and stripe rust (incited by and f. sp. , respectively) was also assessed on the doubled haploids in field trials at three locations in the United States over a 2-year period. Doubled haploids were identified with adult plant resistance to all three rusts, and this germplasm is available to the research and breeding communities.