The adaptation and performance of CIMMYT's bread wheat germplasm (Triticum aestivum> L.) under conditions of low N fertility have been questioned because they were developed under medium‐high levels of N fertility. The objectives of this research were to (i) compare the performance of a set of tall vs. semidwarf cultivars developed by CIMMYT that were widely grown by farmers in the Yaqui Valley of Mexico at low and high N fertility, (ii) measure the genetic progress in grain yield and N use efficiency (NUE), and (iii) evaluate the contribution of N uptake efficiency (UPE) and utilization efficiency (UTE) to NUE. Ten wheat cultivars, two tall and eight semidwarf, produced by CIMMYT and released in the Yaqui Valley of Sonora, by the Mexican government from 1950 to 1985 were grown with 0, 75, 150, or 300 kg N ha−1 in a 3‐yr field study at Ciudad Obregon, Sonora, Mexico. Genetic gains in both grain yield and NUE during 1950 to 1985 were 1.1, 1.0, 1.2, and 1.9% yr−1 on a relative basis or 32, 43, 59, and 89 kg ha−1 yr−1 on an absolute basis, when provided 0, 75,150, and 300 kg ha−1 N, respectively. Progress in NUE resulted in an improvement of both UPE and UTE. However, the relative importance of these two components was affected by the level of applied N. These results contradict the belief that modern semidwarf cultivars require more N than older cultivars. Instead, they respond more to N, which translates into higher economic rates and higher returns when N fertilizer is available.
Germplasm from the spring wheat (Triticum aestivura L.) breeding program at the International Center for Improvement of Maize and Wheat (CIMMYT) has had a major impact on the yield of irrigated spring wheats in most developing countries in the past 30 yr. The rate and nature of yield potential progress in this germplasm was measured comparing eight outstanding short cultivars released in northwest Mexico between 1962 and 1988. They were grown under irrigation and optimal management, including disease and lodging protection, in each of six winter growing seasons (1989-1990 to 1994-1995) at the CIANO (Centro de Investigaciones Agricolas del Noroeste) experiment station in Sonora, Mexico. There were highly significant effects of cultivar on grain yield, and, although cultivar × year interaction was significant, there were few significant crossover interactions between pairs of genotypes and years in the grain yield data set. Yield averaged across the 6 yr increased linearly from 6680 kg ha-~ for the earliest cultivar, Pitic 62, to 8475 kg ha-~ for Bacanora 88, the latest. The rate of progress against year of release was 67 kg ha-~ yr-1 (r = 0.99, P < 0.001), or 0.88% per year. Grain yield progress was correlated with kernel number per square meter (r = 0.84, P < 0.01) and harvest index (r = 0.81, P < 0.02), but not with total biomass production, kernel weight, days to anthesis, spikes per square meter, or kernels per spike. Thus linear progress in yield within short germplasm has continued at least until the late 1980s, and the yield components studied did not indicate any clear direction for future progress, apart from that suggested by the strong relationships between grain yield and harvest index and grain yield and kernels per square meter, as has been seen in most studies of yield progress in cereals.
progress is presented here. While a full understanding of the physiological and genetic basis of yield is still Global demand for wheat (Triticum aestivum L.) is growing faster incomplete, progress has been made in developing selecthan gains in genetic yield potential are being realized, currently a little under 1% per year in most regions. Improvement in yield of tion technologies that may improve the efficiency of semidwarf wheat has generally been associated with increased harvest empirical breeding. Their potential application in breedindex (HI) and grain per square meter. For CIMMYT (International ing to improve the probability of identifying higher-Maize and Wheat Improvement Center) varieties released between yielding genotypes is discussed.1962 and 1988, yield increase was also associated with higher flagleaf photosynthetic rate and related traits, but not higher biomass. Trends in YieldPotential 1966 to Present, Nevertheless, significantly higher biomass has been reported in more and Future Demand recent CIMMYT lines. Improved HI is associated with higher N use efficiency (yield per unit of available N) and improved yield of semi-Though comprehensive studies quantifying genetic dwarf lines is expressed at high and low levels of N input. Where gains in yield potential under irrigated conditions have interplant competition for light and soil factors are manipulated, yield been conducted in relatively few locations, these studies improvement is associated with adaptation to high plant density. Studsuggest steady rates of gains of a little under 1% per ies have confirmed that the juvenile spike growth phase is critical in year since the mid 1960s, for example in India (Kulshresdetermining both grain number and kernel weight (sink) potential. tha and Jain, 1982) and Mexico (Waddington et al., Improving assimilate availability during this stage, perhaps by length-1986, 1987; Sayre et al., 1997). Similar results have been ening its relative duration, may be one way to improve yield potential.shown in studies employing irrigation in high-yielding Traits that could potentially be exploited for improving assimilate (source) capacity include early vigor, stay-green, leaf-angle, and remo-environments such as Italy (Canevara et al., 1994) and bilization of stem reserves. Use of alien chromatin is a successful Argentina (Calderini et al., 1995). Some studies suggest approach for introducing yield-enhancing genes into elite genetic that on-farm wheat yields may have reached a plateau backgrounds. Examples include the 1B/1R chromosome translocation in recent years (Sayre, 1996;. from rye (Secale cereale L.), and more recently the LR19 segment However, the reasons for this can be quite complex, from tall wheatgrass [Agropyron elongatum (Host) P. Beauv.] Iminvolving agronomic and economic factors, and should proving the efficiency of early-generation selection may be another not be confused with the issue of obtaining further gains strategy for raising yield potential by increasing the probability of in genetic yield pot...
Multilocation trials are important for the CIMMYT Bread Wheat Program in producing high-yielding, adapted lines for a wide range of environments. This study investigated procedures for improving predictive success of a yield trial, grouping environments and genotypes into homogeneous subsets, and determining the yield stability of 18 CIMMYT bread wheats evaluated at 25 locations. Additive Main effects and Multiplicative Interaction (AMMI) analysis gave more precise estimates of genotypic yields within locations than means across replicates. This precision facilitated formation by cluster analysis of more cohesive groups of genotypes and locations for biological interpretation of interactions than occurred with unadjusted means. Locations were clustered into two subsets for which genotypes with positive interactions manifested in high, stable yields were identified. The analyses highlighted superior selections with both broad and specific adaptation.
In hexaploid wheat (Triticum aestivum L.) disease resistance genes transferred from alien sources are often associated wilh undesirable traits. Replicated trials using near-isogenic lines of spring wheat 'Seri 82' were conducted for 2 yr under non-moisture stress and simulated moisture stress conditions to determine the effects of the 7DL.7Ag and 1BL.1RS translocations [from Agropyron elongatum (Host) Beauv. and Secale cereale L., respectively] on grain yield and related traits. Mean grain yield of the 1B lines was significantly higher (3.2%) than that of the 1BL.1RS translocation lines in non-moisture stress trials, but not significantly higher in the moisture stress trials. The mean grain yields of the five highest yielding reconstituted Seri 82 genotypes (1BL.1RS) were significantly lower than that of the genotypes without the 1BL.1RS translocation in non-moisture stress (3.2%) and moisture stress (5.2%) conditions. Incorporation of the 7DL.7Ag translocation caused a significant increase (9%) in biomass at harvest in non-moisture stress trials. The mean grain yields of the five highest yielding 7DL.7Ag lines were significantly higher (8.2%) than the reconstituted Seri 82 genotypes in non-moisture stress conditions and more than 16% lower under moisture stress. Lower grain yields of the 7DL.7Ag lines under moisture stress could be due to their excessive pre-heading biomass production. Several yield-related traits of the near-isogenic genotypes varied significantly. Presence of each translocation caused lateness and, when present together, the 1BL.1RS and 7DL.7Ag translocations delayed heading and maturity by 7 and 5 d, respectively. The genetic background of the recipient wheat can affect the utility of a translocation.
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