Submitted to: Yield Gains in Major U.S. Field Crops
Publication Type: Book / Chapter
Publication Acceptance Date: October 17, 2013
Publication Date: June 1, 2014
Citation: Graybosch, R.A., Bockelman, H., Garland-Campbell, K., Garvin, D.F., Regassa, T. 2014. Wheat. In: Smith, S., Diers, B., Specht, J., Carver, B., editors. Yield Gains in Major U.S. Field Crops. CSSA Special Publications 33. Madison, WI: American Society of Agronomy, Inc., Crop Science Society of America, Inc., and Soil Science Society of America, Inc. p. 459-487. Interpretive Summary: Malthusian theory held that human population growth would one-day outstrip agricultural production. Due, in part, however, to the outstanding accomplishments of the Green Revolution, the vision of Malthus remains unfulfilled. Wheat grain yields in the 20th Century, due both to improved agronomic practices and plant breeding, rose at a steady rate. This paper reports on the rate at which wheat grain yield in the US increased in the years since 1980, and the contribution of genetic improvement (wheat breeding) to this increase. Using data from long-term USDA-ARS coordinated regional breeding trials, and data from the University of Nebraska fall-sown winter wheat breeding trials, it was demonstrated that wheat breeders have achieved average increases in grain yield potential of approximately 0.8% per year. This average rate of improvement is slightly less than that achieved by US wheat breeders in the time period 1958-1980. Using identical statistical procedures, previous reports had estimated the rate for the earlier time period at 1.2%. The rate of 0.8% achieved by US breeders was found to be identical to that achieved, on average, in wheat breeding programs across the globe. In two of the analyzed trials, evidence of a yield plateau was revealed. Meeting future world demand for wheat likely will require implementation of an array of techniques for genetic improvement beyond those of classical wheat breeding.
Technical Abstract: Increases in wheat grain yield (kg harvested per hectare) over time derive from improved agronomic practices, and from enhanced genetic potential 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 previous investigations 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. Future prospects for enhanced genetic potential for grain yield in wheat might very well depend upon the application of the tools of genetic engineering, if the exploitable genetic variation for grain yield already has been utilized.