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.
Bibliographical noteFunding Information:
This research was supported by U.S. Department of Agriculture, Agricultural Research Service Non-Assistance Cooperative Agreements ?Developing Northwest-Adapted Barleys With Resistance to Stem Rust? award 58-2072-5-037 and ?Screening Barley Germplasm to Discover Genes Conferring Durable Resistance to Barley Stripe Rust? award 58-2050-6-005. We thank Shiaoman Chao (retired; U.S. Department of Agriculture Agricultural Research Service, Fargo, ND) for Illumina 9K genotyping and allele calling, Rick Gadzinski and Sean Tracey at Functional Biosciences for genotyping and resequencing related to Rpg1 and Rpg5, Austin Case for excellent technical assistance and phenotyping for TTKSK in the Biosafety Level-3 Containment Facility at the University of Minnesota in St. Paul, and the funding received from Comisi?n Nacional de Investigaci?n Cient?fica y Tecnol?gica (CONICYT) Becas-Chile 72160554.
Funding: This research was supported by U.S. Department of Agriculture, Agricultural Research Service Non-Assistance Cooperative Agreements “Developing Northwest-Adapted Barleys With Resistance to Stem Rust” award 58-2072-5-037 and “Screening Barley Germplasm to Discover Genes Conferring Durable Resistance to Barley Stripe Rust” award 58-2050-6-005.