The incidence of epistasis in normal and extreme environments

Abstract

To account for the genotype-environmental interactions which occur between families derived from crosses between the true-breeding varieties 1 and 5 and 2 and 42 of Nicotiana rustica and the environmental variables, sowing date and planting density, it is necessary to include interaction between epistatic gene action and these environmental variables for most characters. In general the epistatic component of the family means is greatest in one or both extremes of the environmental range and is smallest in the other extreme or in the average environments. The change in magnitude and sign of the epistatic component over environments in some but not in all cases is linearly related to biological or physical measures of the differences between the environments. The same character may, therefore, display two or more distinct kinds of genetical architecture in different parts of the environmental range. In average environments most characters display the architecture of a character with an intermediate optimum which has been subjected to stabilizing selection while in optimum at one extreme of the phenotypic range which has been subjected the type of selection to which a phenotype, which deviates from the optimum as defined in an genotype in an environment or an average genotype in an extreme environment. © 1973 The Genetical Society of Great Britain.