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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Synthetic hexaploids (SH) developed at the International Maize and Wheat Improvement Center (CIM-MYT), involving four Triticum turgidum and nine T. tauschii parents, were evaluated for resistance to Karnal bunt (KB) (Tilletia indica Mitra) during three crop seasons over three years at Ciudad Obregon, Sonora, Mexico. Ten tillers of each SH at boot stage, taken at random, were injected with a suspension of sporidia in water (10,000 spores/ml of water). At maturity the inoculated spikes were threshed individually and evaluated for the percentage KB-infected grains. Based on the mean KB score of each entry for three seasons, 49 % of the SH were immune (0 % infection) to KB. Highly resistant expressions characterized the SH which appeared to be influenced by the resistance of their T. turgidum and/or T. tauschii parents. The overall mean infection of the SH wheats was 0.24 % compared to 56.14 % in the susceptible bread wheat check cultivat 'WL711'. Transfer of KB resistance genes from SH wheats into bread wheat is currently underway at CIMMYT.

The effect of the 1AL/IRS chromosome translocation on grain yield and other agronomic characteristics of 85 random F2-derived F6 bulks from three lAL IRS x 1A bread wheat crosses was determined under optimum and reduced irrigation conditions at CIANO, Yaqui Valley, Sonora, Mexico, during the 1991-1992 and 1992-1993 crop production cycles . Harvest plots of 5 .0 m2 were arranged in an alpha lattice design with three replications . The IAL/1 RS translocation increased grain yield, above-ground biomass, spikes/m 2 , and test weight under both irrigated and dryland conditions . Homozygous chromosome 1A lines, on the other hand, possessed longer spikes with more grains . The 1AL/1RS cultivars had an advantage in 1000-grain weight, which was detected only under optimum irrigation . The translocation lines showed later maturity and longer grainfilling period than the 1A genotypes under one irrigation treatment . A significant relationship between grain yield and test weight was detected only among the IAL/1RS genotypes, indicating that they possess heavier and plumper grains than the IA genotypes . These results encourage the continued use of the 1AL/1RS translocation in wheat improvement .

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