Abstract

Stem rust (incited by Puccinia graminis f.sp tritici) is a major disease of wheat and barley. Race TTKSK of stem rust is of particular concern because most cultivars are susceptible. In order to prepare for the possible arrival of stem rust race TTKSK in North America, we crossed a range of barley germplasm - representing different growth habits and end-uses - with donors of Rpg1 and rpg4/Rpg5. The former confers resistance to prevalent races of stem rust in North America and the latter confers resistance to race TTKSK. Using doubled haploids produced from these crosses, we determined allele type at the Rpg loci and haplotype at 9,000 SNP loci. The doubled haploids were phenotyped for TTKSK resistance at the seedling stage. Integration of genotype and phenotype data revealed that Rpg1 was not associated with TTKSK resistance, that rpg4/Rpg5 was necessary but not sufficient for resistance, and that specific haplotypes at two QTLs were required for rpg4/Rpg5 to confer resistance to TTKSK. Adult plant resistance to leaf rust and stripe rust (incited by P. hordei and P. striiformis f.sp. hordei, respectively) was also assessed on the doubled haploids in field trials at three locations in the USA over a two-year period. Adult plant resistance to TTKSK was assessed on a subset of the doubled haploids in Kenya. Doubled haploids were identified with resistance to all of the rusts, and this germplasm is available to the research and breeding communities.