COMPARISON OF 2 CROSSING AND 4 SELECTION SCHEMES FOR YIELD, YIELD TRAITS, AND SLOW RUSTING RESISTANCE TO LEAF RUST IN WHEAT (REPRINTED FROMWHEAT - PROSPECTS FOR GLOBAL IMPROVEMENT, 1998)

The most important breeding objectives in crop improvement are improvi ng grain yield, grain quality, and resistances to various biotic and a biotic stresses. The objectives of our study were to compare two cross ing and four selection schemes for grain yield, yield traits, and slow rusting resistance to leaf rust (Puccinia recondita) based on additiv e genes in wheat (Triticum aestivum), and to identify the most efficie nt crossing and selection methodologies in terms of genetic gains and cost efficiency. Segregating populations were derived from 18 simple c rosses and the same number of top (three-way) crosses. Half of the cro sses were derived from Yecora 70 and the other half from Veery #10 as the common leaf rust susceptible parents. The four selection schemes w ere: pedigree, modified bulk (F-2 and F-1-top as pedigree, selected li nes in F-3, F-4, F-2-top, F-3-top as bulk, and pedigree in F-5 and F-4 -top populations), selected bulk (selected plants in F-2, F-3, F-4, F- 1-top, F-2-top and F-3-top as bulk; and pedigree in F-5 and F-4-top po pulations), and nonselected bulk (bulk in F-2, F-3, F-4, F-1-top, F-2- top and F-3-top; and pedigree in F-5 and F-4-top populations). A total of 320 progeny lines, parents and checks were tested for grain yield, other agronomic traits and leaf rust resistance during the 1992/93 an d 1993/94 seasons in Ciudad Obregon (Sonora State, Mexico) which repre sents a typical high yielding irrigated site. The influence of the typ e of cross and the selection scheme on the mean grain yield and other traits of the progenies was minimal. The selection of parents was the most important feature in imparting yield potential and other favourab le agronomic traits. Moreover, the highest yielding lines were distrib uted equally. Progeny lines derived from Veery #10 crosses had signifi cantly higher mean grain yield compared to those derived from the Yeco ra 70 crosses. Furthermore, a large proportion of the highest yielding lines also originated from Veery #10 crosses. Mean leaf rust severity of the top cross progenies was lower than that of the simple cross pr ogenies possibly because two parents contributed resistance to top cro ss progenies. Mean leaf rust severity of the nonselected bulk derivati ves was twice that of lines derived from the other three schemes. Sele cted bulk appears to be the most attractive selection scheme in terms of genetic gains and cost efficiency.