Classification of Genotype-Environmental Interactions
It is important at the very outset to classify the outward manifestations
of interactions between genotype and environment. The
problem of classification is complex but, as was pointed out by
Haldane (10), certain facts about it are so simple they are usually
not stated. Assume 2 genetically different populations, A and B,
and 2 environments, X and Y. Further assume that measurements
are made on some character (say yield) and that significant differences
are obtained such that the 4 genotype-environment combinations
can be placed in rank order 1 to 4. Twenty-four interaction
types are possible among which 6 are shown in Figure 1. Some
of the points to note about these particular interaction types is
whether genotype A does better than B in each environment (as
in type 1), whether A is superior to B in one environment and
inferior to the other (as in type 4), and whether the change in
environment affects the 2 genotypes in opposite directions (as in
type 3). Each of these interactions represents a type well known
to plant breeders. For example, in types 1 and 3, genotype A can
be taken as the universal variety; in type 6, A and X can be