Reaction of a Group of Related Wheat Species (AABB Genome and an AABBDD) to Stem Rust

Abstract

Accessions of spring habit Triticum spp. with genomes AABB and T. sphaerococcum Percival (genomes AABBDD) were surveyed characterize their reaction to stem rust (Puccinia graminis Pets.: Pers. f. sp. tritici Eriks. & Henn.). Because of the dearth of information in the literature on the reaction of these species to stem rust, the objectives of this study were to screen the accessions for possible new sources of resistance to stem rust, and to postulate the identity of known genes and the minimum number of unknown genes for resistance to stem rust among accessions of each species. Infection‐type data from seedlings of 164 introductions of the USDA National Small Grains Collection artificially infected with 35 isolates of P. graminis tritici were categorized as either low or high infection type. A boxing program based on the gene‐for‐gene concept was used to identify corresponding resistance/avirulence gene pairs. In the combined AABB genomic groups, only 2 of a possible 28 known Sr genes, Sr9f and SrMCN, were among the 35 distinct Sr genes postulated. The other 33 Sr genes were associated with reaction patterns not previously identified. Six accessions were resistant to all isolates and several accessions were resistant to the present prevalent races of the stem rust pathogen in North America. Based on the accessions evaluated, T. sphaerococcum is a poor source of Sr genes for resistance to stem rust.