Mapping and Candidate Gene Analysis of an All-Stage Stem Rust Resistance Gene in Durum Wheat Landrace PI 94701

Puccinia graminis f. sp. tritici (Pgt), the causal agent of wheat stem rust, poses a significant threat to global wheat production. Genetic resistance offers a cost-effective and sustainable solution. The durum wheat landrace PI 94701 was previously hypothesized to carry two stem rust resistance (Sr) genes, but their chromosomal locations were unknown. In this study, we mapped and characterized an all-stage Sr gene in PI 94701, temporarily designated as SrPI94701. In seedling tests, SrPI94701 was effective against all six Pgt races tested. Using a large segregating population, we mapped SrPI94701 on chromosome arm 5BL within a 0.17-cM region flanked by markers pku69124 and pku69228, corresponding to 1.04 and 2.15 Mb genomic regions in the Svevo and Chinese Spring reference genomes. Within the candidate region, eight genes exhibited differential expression between the Pgt-inoculated resistant and susceptible plants. Among them, two nucleotide-binding leucine-rich repeat (NLR) genes, TraesCS5B03G1334700 and TraesCS5B03G1335100, showed high polymorphism between the parental lines and were upregulated in Pgt-inoculated resistant plants. However, the flanking and completely linked markers developed in this study could not accurately predict the presence of SrPI94701 in a survey of 104 wheat accessions. SrPI94701 is a promising resource for enhancing stem rust resistance in wheat breeding programs.