Characterization and identification of sources of rust resistance in Triticum militinae derivatives.

Triticum militinae (2n = 4X = 28, AtAtGG), belonging to the secondary gene pool of wheat, is known to carry resistance to many diseases. Though some disease resistance genes were reported from T. timopheevii, the closest wild relative of T. militinae, there are no reports from T. militinae. Twenty-one T. militinae Derivatives (TMD lines) developed at the Division of Genetics, IARI, New Delhi, were evaluated for leaf and stripe rusts at seedling and adult plant stages. Eight TMD lines (6-4, 6-5, 11-6, 12-4, 12-8, 12-12, 13-7 and 13-9) showed seedling resistance to both leaf and stripe rusts while six TMD lines (7-5, 7-6, 11-5, 13-1, 13-3 and 13-4) showed seedling resistance to leaf rust but adult plant resistance to stripe rust and three TMD lines (9-1, 9-2 and 15) showed seedling resistance to leaf rust but susceptibility to stripe rust. Three TMD lines (2-7, 2-8 and 6-1) with adult plant resistance to leaf and stripe rusts were found to carry the known gene Lr34/Yr18. Ten TMD lines (7-5, 7-6, 9-1, 9-2, 11-5, 11-6, 12-12, 12-4, 12-8, and 15) with seedling resistance to leaf rust, showing absence of known genes Lr18 and Lr50 with linked markers requires further confirmation by the test of allelism studies. As not a single stripe rust resistance gene has been reported from T. militinae or its close relative T. timpopheevii, all the 8 TMD lines (6-4, 6-5, 11-6,12-4, 12-8, 12-12, 13-7 and 13-9) identified of carrying seedling resistance to stripe rust and 3 TMD lines (13-1, 13-3 and 13-4) identified of carrying adult plant resistance to stripe rust are expected to carry unknown genes. Also, all the TMD lines were found to be cytologically stable and thus can be used in inheritance and mapping studies.

Marker-assisted transfer of leaf and stripe rust resistance from Triticum turgidum var. durum cv. Trinakria to wheat variety HD2932.

A marker-assisted backcrossing program initiated to transfer leaf rust resistance gene LrTrk from Triticum turgidum cv. Trinakria to hexaploid wheat variety HD2932 cotransferred a stripe rust resistance gene, YrTrk, along with LrTrk. The cross of hexaploid recurrent parent HD2932 with tetraploid donor parent Trinakria produced pentaploid F1 plants. F1s were backcrossed with recurrent parent HD2932 to produce BC1F1 generation. Foreground and background selection was conducted in each backcross generation to identify plants for backcrossing or selfing. While foreground selection for LrTrk was carried out with linked and validated molecular marker Xgwm234, for background selection, 86 polymorphic SSR markers from the A and B genomes were used. Single selected plants from BC1F1 and BC2F1 generations backcrossed and selfed to produce BC2F1and BC2F2 generations, respectively. Background selection resulted in 83.72%, 91.86%, and 98.25% of RPG recovery in BC1F1, BC2F1, and BC2F2 generations, respectively. A total of 27 plants with LrTrk in homozygous state were identified in BC2F2 generation and selfed to produce 27 BC2F3 NILs. All the NILs were tested for leaf and stripe rust resistance at the seedling stage using seven Puccinia triticina and one Puccinia striiformis f.sp. tritici rust pathotypes. All the 27 NILs were found to be resistant to both leaf and stripe rust pathotypes. So, these NILs are designated to carry leaf and stripe rust resistance genes LrTrk/YrTrk.

Marker-Assisted Improvement of Bread Wheat Variety HD2967 for Leaf and Stripe Rust Resistance.

The mega wheat variety HD2967 was improved for leaf and stripe rust resistance by marker-assisted backcross breeding. After its release in 2011, HD2967 became susceptible to stripe rust and moderately susceptible to leaf rust. The leaf rust resistance gene LrTrk was transferred into HD2967 from the durum wheat genotype Trinakria. Then, HD2967 was crossed with Trinakria to produce F1 plant foreground selection for LrTrk and background selection for the recurrent parent genotype was carried out in BC1F1, BC2F1 and BC2F2 generations. Foreground selection was carried out with the linked marker Xgwm234, while polymorphic SSR markers between parents were used for background selection. Background selection resulted in the rapid recovery of the recurrent parent genome. A morphological evaluation of 6 near isogenic lines (NILs)-2 resistant to leaf and stripe rust, and 4 resistant to leaf rust only-showed no significant differences in yields among NILs and the recurrent parent HD2967. All of the 6 NILs showed the presence of 2NS/2AS translocation, carrying the linked genes Lr37/Sr38/Yr17 present in HD2967 and the targeted leaf rust resistance gene LrTrk. Two NILs also showed additional resistance to stripe rust. Therefore, these NILs with rust resistance and an at par yielding ability of H2967 can replace the susceptible cultivar HD2967 to reduce yield losses due to disease.