Marker-assisted development and characterization of a set of Triticum aestivum lines carrying different introgressions from the T. timopheevii genome

A set of common wheat introgression lines carrying one or two introgressions from Triticum timopheevii was produced by means of marker-assisted backcross selection. The starting material consisted of two BC1F20 (T. aestivum*2/T. timopheevii) lines with resistance to leaf rust, stem rust, powdery mildew, spot blotch, and loose smut and containing multiple 1Aᵗ, 2Aᵗ, 2G, 3AᵗL, 3GL, 4GL, 5AᵗL, 5GL, and 6G T. timopheevii chromosome fragments. The two lines were crossed with, and backcrossed three times to common wheat cultivar Saratovskaya 29. In total, 275 BC2F1 and BC3F2 plants were characterized by microsatellite markers and in situ hybridization. Molecular and cytological analyses revealed 38 plants with a single introgression from chromosomes 2G, 5GL, or 6G of T. timopheevii and 72 plants, each with two introgressions, among them three plants carrying a T. timopheevii translocation involving the D genome (2DS.2GL). It was observed that the lengths of fragments introgressed from the Aᵗ genome were more than halved in the BC2 generation, while the lengths of 2G and 5GL introgressed fragments were only slightly reduced after the third backcross. The introgression lines were tested for resistance to the native Puccinia triticina population of the Western Siberian region of Russia. Lines with a single introgressed 5GL region carrying the major leaf rust resistance locus, QLr.icg-5B, were completely resistant. The presence of two minor resistance loci, QLr.icg-2A and QLr.icg-1A, suppressed disease development and reduced the number of urediniospores by up to 25 % but did not lead to a hypersensitive response. The introgression lines therefore constitute promising sources of new resistance to Puccinia triticina.