Introgression of rpg4/Rpg5 Into Barley Germplasm Provides Insights Into the Genetics of Resistance to Puccinia graminis f. sp. tritici Race TTKSK and Resources for Developing Resistant Cultivars.

Stem rust (incited by Puccinia graminis f. sp. tritici) is a devastating disease of wheat and barley in many production areas. The widely virulent African P. graminis f. sp. tritici 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 Rpg1 and rpg4/Rpg5. The former confers resistance to prevalent races of P. graminis f. sp. tritici 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 Rpg 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) Rpg1 was not associated with TTKSK resistance, (ii) rpg4/Rpg5 was necessary but was not sufficient for resistance, and (iii) specific haplotypes at two quantitative trait loci were required for rpg4/Rpg5 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 Puccinia hordei and Puccinia striiformis f. sp. hordei, 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.

FR-H3: a new QTL to assist in the development of fall-sown barley with superior low temperature tolerance.

Fall-sown barley will be increasingly important in the era of climate change due to higher yield potential and efficient use of water resources. Resistance/tolerance to abiotic stresses will be critical, and foremost among the abiotic stresses is low temperature. Simultaneous gene discovery and breeding will accelerate the development of agronomically relevant fall-sown barley germplasm with resistance to low temperature. We developed two doubled haploid mapping populations using two lines from the University of Nebraska (NE) and one line from Oregon State University (OR): NB3437f/OR71 (facultative × facultative) and NB713/OR71 (winter × facultative). Both were genotyped with a custom 384 oligonucleotide pool assay (OPA). QTL analyses were performed for low temperature tolerance (LTT) and vernalization sensitivity (VS). The role of VRN-H2 in VS was confirmed and a novel alternative winter allele at VRN-H3 was discovered in the Nebraska germplasm. FR-H2 was identified as a probable determinant of LTT and a new QTL, FR-H3, was discovered on chromosome 1H that accounted for up to 48 % of the phenotypic variation in field survival at St. Paul, MN, USA. The discovery of FR-H3 is a significant advancement in barley LTT genetics and will assist in developing the next generation of fall-sown varieties.