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.