RELATIONSHIPS AMONG ANALYTICAL METHODS USED TO STUDY GENOTYPIC VARIATION AND GENOTYPE-BY-ENVIRONMENT INTERACTION IN PLANT-BREEDING MULTI ENVIRONMENT EXPERIMENTS
M. Cooper et Ih. Delacy, RELATIONSHIPS AMONG ANALYTICAL METHODS USED TO STUDY GENOTYPIC VARIATION AND GENOTYPE-BY-ENVIRONMENT INTERACTION IN PLANT-BREEDING MULTI ENVIRONMENT EXPERIMENTS, Theoretical and Applied Genetics, 88(5), 1994, pp. 561-572
Following the recognition of the importance of dealing with the effect
s of genotype-by-environment (G x E) interaction in multi-environment
testing of genotypes in plant breeding programs, there has been substa
ntial development in the area of analytical methodology to quantify an
d describe these interactions. Three major areas where there have been
developments are the analysis of variance, indirect selection, and pa
ttern analysis methodologies. This has resulted in a wide range of ana
lytical methods each with their own advocates. There is little doubt t
hat the development of these methodologies has greatly contributed to
an enhanced understanding of the magnitude and form of G x E interacti
ons and our ability to quantify their presence in a multi-environment
experiment. However, our understanding of the environmental and physio
logical bases of the nature of G x E interactions in plant breeding ha
s not improved commensurably with the availability of these methodolog
ies. This may in part be due to concentration on the statistical aspec
ts of the analytical methodologies rather than on the complementary re
solution of the biological basis of the differences in genotypic adapt
ation observed in plant breeding experiments. There are clear relation
ships between many of the analytical methodologies used for studying g
enotypic variation and G x E interaction in plant breeding experiments
. However, from the numerous discussions on the relative merits of alt
ernative ways of analysing G x E interactions which can be found in th
e literature, these relationships do not appear to be widely appreciat
ed. This paper outlines the relevant theoretical relationships between
the analysis of variance, indirect selection and pattern analysis met
hodologies and their practical implications for the plant breeder inte
rested in assessing the effects of G x E interaction on the response t
o selection. The variance components estimated from the combined analy
sis of variance can be used to judge the relative magnitude of genotyp
ic and G x E interaction variance. Where concern is on the effect of l
ack of correlation among environments, the G x E interaction component
can be partitioned into a component due to heterogeneity of genotypic
variance among environments and another due to the lack of correlatio
n among environments. In addition, the pooled genetic correlation amon
g all environments can be estimated as the intraclass correlation from
the variance components of the combined analysis of variance. Where G
x E interaction accounts for a large proportion of the variation amon
g genotypes, the individual genetic correlations between environments
could be investigated rather than the pooled genetic correlation. Indi
rect selection theory can be applied to the case where the same charac
ter is measured on the same genotypes in different environments. Where
there are no correlations of error effects among environments, the ph
enotypic correlation between environments may be used to investigate i
ndirect response to selection. Pattern analysis (classification and or
dination) methods based on standardised data can be used to summarise
the relationships among environments in terms of the scope to exploit
indirect selection. With the availability of this range of analytical
methodology, it is now possible to investigate the results of more com
prehensive experiments which attempt to understand the nature of diffe
rences in genotypic adaptation. Hence a greater focus of interest on u
nderstanding the causes of the interaction can be achieved.