Phenotypic Plasticity of Growing Degree-Days to Heading and of Grain Yield in a Multi-Environment Trial of Winter Wheat.

A single plant genotype may produce a range of different phenotypes under varying environmental conditions. The flexibility of a phenotype under these different conditions is known as plasticity for that trait. Plasticity is unique to the germplasm, environments, and trait evaluated. We characterized variability in grain yield and growing degree-days to heading (GDD) in a panel of 299 hard winter wheat (Triticum aestivum L.) genotypes that were grown at 11 different U.S. Great Plains environments in 2012 and 2013.  Phenotypic plasticity of GDD (GDDP) and grain yield for each genotype was estimated as the slope obtained by regressing the genotype mean on the environmental mean. The extent of plasticity was 0.68 to 1.41 for GDD and 0.64 to 1.37 for grain yield, indicating a broad range of responsiveness among the genotypes to environmental conditions. Plasticity of GDD was negatively associated with grain yield, indicating high values of plasticity were detrimental among the germplasm and environments evaluated. High GDD plasticity was especially detrimental in the lowest-yielding environments. High values of yield plasticity were positively associated with both lowest and highest yields, indicating high levels of yield plasticity were beneficial. High values of yield plasticity were especially beneficial under favorable conditions. More than a century of wheat breeding in this region suggests GDDP has declined and yield plasticity has increased at similar rates. Changes in plasticity over time suggest these traits are responding to indirect selection. Yield plasticity and GDD plasticity are inversely related, which suggests the favorable traits (high yield plasticity, low GDD plasticity) could be directly selected for simultaneously.