GERMPLASM ENHANCEMENT IN WINTER-WHEAT X TRITICUM-TAUSCHII BACKCROSS POPULATIONS

Backcross populations derived from direct hybrids between common wheat (Triticum aestivum L.) and the wild diploid T. tauschii (Coss.) Schmal. have utility for germplasm evaluation, but also can furnish genetic material directly into a germplasm-enhancement program. Three hundred ninety-one BC2F2-derived lines from winter wheat x T. tauschii crosses were selected on the basis of disease resistance and general phenotype from populations undergoing field evaluation to determine whether resistant lines agronomically similar or superior to their recurrent parents could be developed. The selected backcross lines were evaluated for yield and grain-quality traits under light to moderate infection by leaf rust (caused by Puccinia recondita f. sp. tritici Rob. ex Desm.) and heavy infection by wheat soilborne mosaic and spindle-streak mosaic viruses at two locations in 1991. Approximately 50% of the lines were selected for further field evaluation at two locations in 1992, and three lines were entered in advanced yield trials in a total of eight environments in 1992 and 1993. At all stages of selection, BC2F2-derived Lines were identified with disease resistance, grain yield, and grain quality superior to those of their recurrent parents. Lines differing from their recurrent parents in grain yield, either positively or negatively, occurred in both the disease-resistant and disease-susceptible classes. In advanced yield trials where leaf rust did not affect grain yield, leaf rust-resistant BC2F2-derived lines yielded similarly to their recurrent parents and to cultivars currently grown commercially over large areas. Despite the wide differences in phenotype between common wheat and T. tauschii, two backcrosses were sufficient to transfer resistance genes while almost the wheat parent's phenotype.