A Thinopyrum intermedium chromosome in bread wheat cultivars as a source of genes conferring resistance to fungal diseases

Wheatgrass Thinopyrum intermedium (Host), or Agropyron intermedium (Host) (2n = 42; genome formula, EEE(st)E(st)StSt) is one of the most valuable sources of highly effective resistance genes in wheat breeding. Bread wheat cultivars Tulaikovskaya 5, Tulaikovskaya 10, and Tulaikovskaya 100 derived from wheat-Thinopyrum crosses are highly resistant to leaf rust and powdery mildew, and moderately resistant to stem and yellow rust. C-banding, in situ hybridization, and assays with PLUG and SSR markers have demonstrated that wheat chromosome 6D in all three cultivars is substituted by the Th. intermedium homoeologous chromosome, 6Ai. This chromosome was designated 6Ai#2, because it differs from the earlier described homoeologous chromosome 6Ai#1. In situ hybridization with Pseudoroegneria spicata and Dasypyrum villosum genomic DNAs has allowed chromosome 6Ai#2 to be assigned to the E (=J) subgenome. Chromosome 6Ai#2 remained intact over long-term breeding efforts. Tests of leaf rust resistance of in F-2 and F-3 populations from a cross of a leaf rust-susceptible cultivar with Tulaikovskaya 10 has demonstrated that chromosome 6Ai#2 carries at least one gene locus for leaf rust resistance. This locus was designated Lr6Ai#2. It must be different from the known gene locus Lr38, located on the long arm of chromosome 7Ai#2 and now present in many translocation variants in bread wheat. The effect of a chromosome from the Th. intermedium subgenome E on resistance to powdery mildew, stem and yellow rust in Tulaikovskaya 5, Tulaikovskaya 10, and Tulaikovskaya 100 is discussed.