Genetic Improvement in Winter Wheat Yields in the Great Plains of North America, 1959-2008

Data from USDA-coordinated winter wheat (Triticum aestivum L.) regional performance nurseries collected over the time period 1959 to 2008 were used to estimate genetic gain (loss) in grain yield, grain volume weight, days to heading, and plant height in winter wheats adapted to the Great Plains of North America. In both the Southern Regional (SRPN) and Northern Regional Performance Nurseries (NRPN), linear regression revealed significant positive relationships between relative grain yields of advanced breeding lines and calendar year of the nursery trial. The estimated genetic gain in grain yield potential since 1959 was approximately 1.1% (of the control cultivar Kharkof) yr(-1) for all entries in the SRPN, and 1.3% yr(-1) if only the most productive entry was considered. For the NRPN, the estimates of genetic gain in grain yield were 0.79% yr(-1) for all entries, and also 0.79% yr(-1) for the most productive entry. Linear regressions of relative grain yields vs. year over the time period 1984 to 2008, however, showed no statistically significant trend in the SRPN. For the same time period in the NRPN, a statistically significant positive slope of 0.83 was observed, though the coefficient of determination (R-2) was only 0.28. Relative grain yields of Great Plains hard winter wheats may have peaked in the early to mid-1990s, and further improvement in the genetic potential for grain yield awaits some new technological or biological advance.