Nearly 50 percent of the 1988 advanced breeding lines of the CIMMYT bread wheat breeding program possess the lB/lR homozygous translocation. Hence, a trial was conducted to estimate the effect of lB/lR chromosome translocation on the yield potential of some of our high-yielding spring wheats, where non-limiting levels of fertility, moisture, preventive pest and disease programs were used. In conclusing the lB/lR lines seemed to have increased their above-ground biomass yield, number of spikes per meter"^, 1000-grain weight and test weight. They also exhibited a slight advantage over the IB homozygous lines on grain yield. The observed difference, however, was non-significant, as was the plant height difference observed among the two groups. Varietal comparisons indicated that the IB/ IR group headed later than the IB group.

Comparisons involving 28 random F2-derived F5 wheat {Triticum aestivum L.) lines from the cross, 'Nacozari'/'Seri 82', suggested that advanced derivatives with the 1BL/1RS chromosome translocation possess superior agronomic performance in both full and reduced irrigation conditions when compared with IB derivatives. This performance advantage was attributed to high grain yield, above-ground biomass at maturity, grains/spike, 1000-grain weight and test weight. The lBL/lRS hnes were shorter with delayed flowering and maturity. The superiority of the lBL/lRS translocation group on grains/m^ was expressed only under the full irrigation environment. Higher harvest index, longer spike-length and grain-filling period were detected only under reduced irrigation conditions. A significant grain yield relationship with test weight was detected only among the lBL/lRS genotypes, indicating that they possess heavier and plumper grains than the IB genotypes.Key words: Secale cereale -Triticum translocation -yield components aestivum -1 BL/1 RS The lBL/lRS chromosome translocation containing the IRS arm from rye has been incorporated globally into many hexaploid wheat (Triticum aestivum L.; 2n = 6X = 42; AABBDD) cultivars (Jahan et al. 1990, Lukaszewski 1990, Mettin et al. 1973, Zeller 1973, and to a limited extent in durum wheat {T. turgidum L.) 2n = 4X = 28, AABB (Friebe et al. 1987). In addition to protection of high-yield potential by resistance genes on the rye arm (McIntosh 1983), some researchers have perceived a yield increase associated with the lBL/lRS translocation (Rajaram et al. 1983).1 rials conducted in Mexico comparing 10 high-yielding spring wheats, five with the 1BL/1 RS translocation, and five with the normal IB chromosome, demonstrated that genotypes with the lBL/lRS chromosome translocation had higher aboveground biomass at maturity, 1000-grain weight, test weight and number of spikes/m^. Although the lBL/lRS cultivars appeared to have a slight advantage in grain yield, the observed difference was not significant (Villareal et al. 1991(Villareal et al. , 1994. In a similar study using F3-derived ¥(, and F7 winter wheat lines from the 'Siouxland'/'Ram' cross, comparisons showed a 9% yield increase of lBL/lRS genotypes over IB genotypes (MorenoSevilla 1994). They attributed this trend to postanthesis stress tolerance of the lBL/lRS genotypes which resulted in increased kernel weight. Recently, Carver and Rayburn (1994) reported 9-10% higher grain yield, 11-12% more aerial biomass, and 4-6% increase in kernel weight in lBL/lRS over IB near-isoUnes derived from two hard red winter-wheat populations.Demonstration of the yield advantage of lBL/lRS translocation in winter wheats has not been reported in spring wheats by evaluation of a stringent germplasm set. As about 50% of CIMMYT advanced high-yielding bread wheat lines possess the lBL/lRS translocation, it is imperative that further investigations be conducted to verify this grain yield advantage of the lBL/lRS germplasm. This study was conducted to determine t...

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