Genetic Contributions to Yield Gains in US Wheat, 1980-2010.

Increases in wheat grain yield (kg harvested per hectare) over time derive from improved agronomic practices, and from genetic improvement of wheat cultivars.  Estimation of the rate of genetic improvement over time is important as it allows prediction of whether future grain supplies will meet future demands of world population.    In this study, wheat grain yields relative to check cultivars in USDA-ARS coordinated regional performance trials were calculated for the time period 1980-2010, and regression analysis used to evaluate changes in relative grain yield potential versus year of the trial.  The results were compared to those of a previous investigation in which an identical approach was used for the time period 1958-1980.    Averaged across all trials, the genetic potential for grain yield increased from 1980 to 2010 at a rate of approximately 0.8% per year, lower than the value of 1.2% reported for the time period 1958 – 1980.  The observed rates of increase were statistically different (p=0.05) from zero for all USDA-ARS performance nurseries with the exception of the Southern Regional Performance Nursery and the Pacific Northwest  Soft Winter Wheat nursery.  These two trials represent the lowest, and highest yielding environments, suggesting that genetic progress has been difficult when either moisture is often limiting, or when wheat yields are approaching biological limits.  The average rate of improvement observed for US wheats (0.8% per year) was identical to that observed from a literature survey of experiments across the globe.