Bread Wheat Cultivars with 6D(6Ai) Substitution as a Source of Genes Conferring Resistance to Leaf and Stem Rust

Wheatgrass Thinopyrum intermedium (Host), or Agropyron intermedium (Host) (2n = 42; genome formula, EEE^stE^stStSt) 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 carry wheatgrass genetic material. C-banding, in situ hybridization, and SSR analyses have demonstrated that in all three wheat cultivars the chromosome 6D is substituted by a chromosome of Th. intermedium, which was designated 6Ai#2 to discriminate it from the earlier described wheatgrass chromosome 6Ai#1. Chromosome 6Ai#2 remained intact over long-term breeding efforts. MAS of F₂ and F₃ populations from a cross of a leaf rust–susceptible cultivar with Tulaikovskaya 10 has demonstrated that the chromosome 6Ai#2 carried new gene for leaf rust resistance, designated Lr6Ai#2. This gene was shown to be different from already known Lr38, mapped to the long arm of chromosome 7Ai#2, translocated to wheat chromosome 7DL; this translocation variant was detected in many modern cultivars of bread wheat.

One hundred sixty five wheat lines from Kazakhstan, Siberia and Volga region were tested to U99 stem rust resistance in Kenya. According to the results of PCR with markers specific to 6Ai#2 42 of these lines had the wheatgrass chromosome. Their screening with the original race Ug99 (TTKSK) has demonstrated that 50% lines carrying Sr6Ai#2 gene and 100% lines carrying two genes (Sr6Ai#2+Sr25) showed high to moderate resistance to Ug99.

The work of EAS, AIS, INL, IGA was supported by Federal Targeted Program of the Russian Federation (agreement no. 14.604.21.0106).