Characterization of Adult Plant Resistance to Predominant Chinese Races of <i>Puccinia graminis</i> f. sp. <i>tritici</i> and Stem Rust Resistance Genes in US Wheat Accessions

Wheat stem rust, caused by Puccinia graminis f. sp. tritici, is a devastating disease occurring in most wheat growing countries and regions, posing a severe threat to global wheat production and food security. The deployment of resistant wheat cultivars is widely recognized as the most economical, effective, and environmentally sustainable approach for controlling this disease. To identify novel and effective resistance resources, 105 wheat accessions introduced from the United States were evaluated for adult plant resistance against two predominant Chinese P. graminis f. sp. tritici races (21C3CTHQM and 34MKGQM) in field trials conducted during 2023 and 2024. Molecular marker detection was further performed to assess the presence of five known stem rust resistance genes (Sr24, Sr31, Sr25, Sr26, Sr38). Field results across two consecutive years demonstrated that more than 70% of the tested accessions exhibited high levels of resistance to the two P. graminis f. sp. tritici races. Molecular genotyping indicated that 13 accessions (12.4%) carried only the Sr24 resistance gene, two accessions (1.9%) carried only Sr31, and two accessions (1.9%) carried both Sr24 and Sr31. None of the tested resistance genes (Sr24, Sr31, Sr25, Sr26, Sr38) were detected in the remaining 89 accessions. Notably, although over 70% of the wheat accessions displayed stable and high resistance, only 16.2% carried the known resistance genes Sr24 or Sr31. The remaining resistant accessions (84.8%) likely harbor uncharacterized resistance genes, which can serve as valuable and novel genetic resources for wheat stem rust resistance breeding.