Genotype × Environment Interaction
The genotypic value of some candidate was defined to be equal to the expected phenotypic value at given macro-environmental conditions. This means that the genotypic value of a given candidate depends on the macro-environmental growing conditions. It also means that differences between candidates depend on the macro-environmental conditions. This phenomenon is called genotype by environment interaction (g x e interaction). It may even mean that ranking of candidates according to their genotypic value depends on the macroenvironmental growing conditions. The latter is a disturbance to breeders, who generally want to select candidates performing, under diverse conditions, in a superior way. The phenomenon is also disturbing when testing varieties developed for hopefully a wide range of conditions. This chapter elaborates some relevant aspects of g x e interaction.