Date of this Version
Crop Science, Vol. 52, March–April 2012; doi: 10.2135/cropsci2011.08.0412
A previous investigation, using region-wide data from Great Plains wheat (Triticum aestivum L.) breeding trials, indicated a possible plateau in the rate of genetically determined yield potential. Data from the same USDA- Agricultural Research Service (ARS) coordinated long-term regional performance nurseries was used to further examine the rate of genetic improvement of Great Plains winter wheats in specific agroecological or production zones over the time period 1987 to 2010. The absolute grain yield of all entries and of the top fi ve most productive entries increased in the majority of production zones over this time period. The relative rate of genetic improvement, obtained by comparing grain yields to those of the long-term control cultivar Kharkof, ranged from not significantly different from zero to 1.98% yr–1. This rate of change, however, was statistically significant (α = 0.05) in only two of the 12 zones evaluated. Variance components identified production zone and locations within production zone as being the largest sources of variation in grain yields. Variance due to either genotype or genotype × environmental factors remained both constant over the 24-yr time period and small, relative to the environmental variances. Genetic progress for enhanced wheat yield in the region might be limited by the magnitude of these environmental variances and by constraints arising from continuous evolution of pest and pathogen populations.