The relation between hybrid vigour and genotype-environment interactions.

Consideration was given to the response curves and response surfaces that are obtained when genotypes are grown at various levels of environmental factors. These curves and surfaces were used to illustrate genotype-environment interactions and possible relations between two parents and their F 1.When a hybrid had a response exactly intermediate between its parents, the metric values for the hybrid were not intermediate but varied with the environment, exhibiting different degrees of dominance including overdominance (hybrid vigour). A range in dominance for the metric also was found when the response of the hybrid was more similar to one parent than the other.A hybrid with an intermediate response has a lower phenotypic variance across environments than the mean variance of its parents. In some situations the hybrid's variance is less than that of either parent.A component of the error variation for a genotype was shown to vary with the environment having a minimal value when the environment was optimal.An algebraic treatment of response curves and surfaces was presented. In some instances the metric values for two parents and their F 1 in a range of environments may be related in the form of a multiple regression.