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Trends in Winter Wheat Performance as Measured in International Trials¹

Multiple-year testing periods of an International Winter Wheat Performance Nursery (IWWPN) were compared to identify a yield trend for modern winter wheats and to assess the genetic contribution to any predicted yield gain. Average grain protein concentration, plant height, and 1000-kernel weight values of the most productive cultivar in each trial were examined to determine whether simultaneous trends for these traits could be established and/or correlated with yield performance. Data from a uniform set of sites over 12 test periods from 1970 to 1983 indicated yield advancement from 4075 to 5946 kg ha^–1 for the most productive wheat (Triticum aestivum L.) cultivars. Of this gain, 57% was attributable to improvements in cultural techniques whereas 43% was due to genetic improvements. When data from all reporting test sites were used, predicted yields advanced from 4022 to 5326 kg ha^–1 with 55% of the gain attributable to genetic improvement. A slowing in the rate of yield increase was not detected among the most productive wheat cultivars in this study. Generally, increased grain production levels are associated with reductions in grain protein concentration. However, the increased grain yields in the IWWPN were not associated with significant reductions in grain protein concentration. Relative to the long-term check, ‘Bezostaya 1’, grain yields of the most productive cultivars in the IWWPN showed a significant increase from 1970 to 1983, while the grain protein concentration of these cultivars remained essentially constant. Since high yielding semi-dwarf wheats succeeded many of the older standard-height cultivars during the 1970s it was of interest to determine whether a correlated response between higher yields and reduced height would be apparent among the IWWPN cultivars. Plant height of the most productive cultivars was variable and not closely associated with grain yield per se. Although a trend toward shorter height of these cultivars was not apparent, more of the recently tested cultivars in the IWWPN have been short in stature. The average height of the three most productive cultivars per trial has shown a significant decline from 1970 to 1983. Kernel weight values were variable and not closely correlated with advances in grain yield.

Key Words: Triticum aestivum L. • Yield trends • Genetic gain

² Research geneticist, leader wheat research, and research agronomist, respectively, USDA-ARS, Lincoln, NE; and professor, Univ. of Nebraska-Lincoln, Lincoln, NE 68583.

Received for publication December 17, 1984.