Improvement in the Yield Potential of Bread Wheat Adapted to Northwest Mexico1

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Abstract
Two trials were conducted at the Mexican National Institute of Agricultural Research (INIA) experimental station, Yaqui Valley, Sonora, Mexico, to determine the genetic yield potential of bread wheat (Triticum aestivum L.) cultivars released in northwest Mexico over the period from 1950 to 1982, with emphasis on progress since 1970. Nonlimiting levels of fertility and moisture, a preventative pest and disease program, and netting to prevent lodging were used. Grain yield, yield components, and rates of phytomass production and grain filling were determined. Yield data on selected genotypes grown in 4 yrs of the International Spring Wheat Yield Nursery (ISWYN) at the same station were also examined. The grain yield potential of cultivars, successively released since 1950, has risen at an estimated (from a regression slope) average of 59 kg/ha/yr of release, or about 1.1%/yr. Although yield potential may have plateaued in the early 1970s, cultivars released since 1979, i.e., modern genotypes (e.g., ‘Ciano 79’, ‘Genaro 81’, ‘Glennson 81’, and ‘Seri 82’) have improved yield potential at an estimated rate similar to that prior to 1970. Improvements in grain yield were associated with increases in grain number per unit area (r = 0.74, P < 0.01), which has risen by about 34% in modern genotypes compared to pre‐1970 cultivars, and grain number per spike (r = 0.51, Pr = −0.76, P2) and greater C assimilation during a longer preanthesis phase.