Theoretical Aspects of Selection for Yield in Stress and Non-Stress Environment
The question of choice of selection criterion when lines are grown in stress and non-stress environments is examined from a theoretical standpoint in this paper. Tolerance to stress is defined as the difference in yield between stress and non-stress environments, while mean productivity is the average yield in stress and non-stress environments. Equations are developed for the genetic correlations of tolerance and mean productivity with one another and with yields in stress and non-stress environments in terms of the ratio of genetic variances and the genetic correlations between yields in stress and non-stress environments. These equations show that selection for tolerance to stress will generally result in a reduced mean yield in non-stress environments and a decrease in mean productivity. Selection for mean productivity will generally increase mean yields in both stress and non-stress environments. Tolerance and mean productivity show negative genetic correlations whent he genetic variance in stress environmentsi s less than the genetic variance in non-stress environments. This result provides an explanation for the positive correlations often reported between regression coefficient stability and mean productivity; a line with high tolerance to stress normally would have a low regression coefficient stability and genetic variances in stress environments are generally lower than in non-stress enviornments.
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