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

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, P<0.05). The 1000-grain weight, was reduced slightly in the modern high grain number cultivars (r = –0.76, P<0.01). Harvest indices for modern genotypes were lower than those of the landmark cultivar ‘Yecora 70’, but the modern genotypes had, on average, 16% greater phytomass than pre-1970 cultivars. However, only 43% of the variation in grain yield was attributable to phytomass. The improvements in yield potential are mainly the result of empirical selection for grain yield. Indications were that rates of grain filling and phytomass production in modern genotypes were similar to those in Yecora 70. The higher grain yield and phytomass in modern genotypes compared to Yecora 70 was probably due to the formation and survival of a larger grain sink (more grains/m²) and greater C assimilation during a longer preanthesis phase.

Key Words: International Spring Wheat Yield Nursery (ISWYN) • Grain yield • Grain-filling rate • Harvest index • Phytomass • Triticum aestivum L. • Yield components

² Former postdoctoral fellow (now regional agronomist, CIMMYT Maize Program, P.O. Box MP163, Mount Pleasant, Harare, Zimbabwe); former agronomist (now regional agronomist, CIMMYT Maize Program, P.O. Box 25171, Nairobi, Kenya); and associate scientist and agronomist (present address, CIMMYT Wheat Program, 3rd Floor, Dep. of Agric., Bangkhen, Bangkok 10900, Thailand) respectively, CIMMYT Wheat Program, Mexico.

Received for publication January 25, 1985.

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