A PROCEDURE TO ASSESS THE RELATIVE MERIT OF CLASSIFICATION STRATEGIESFOR GROUPING ENVIRONMENTS TO ASSIST SELECTION IN PLANT-BREEDING REGIONAL EVALUATION TRIALS
M. Cooper et al., A PROCEDURE TO ASSESS THE RELATIVE MERIT OF CLASSIFICATION STRATEGIESFOR GROUPING ENVIRONMENTS TO ASSIST SELECTION IN PLANT-BREEDING REGIONAL EVALUATION TRIALS, Field crops research, 35(1), 1993, pp. 63-74
Classification methodology is widely used by plant breeders to group e
nvironments on the results of regional evaluation trials to assist in
selection among genotypes. To be effective, this strategy must be inte
grated with the theory of indirect selection. Environments which group
together should reflect commonality of genotypic discrimination and t
herefore give rise to similar selection among genotypes. Four strategi
es for classifying environments were compared. These were based on unt
ransformed and three forms of transformed data (coded, standardised an
d rank). Th comparison assessed how effectively the groups of environm
ents formed by using each transformation maximised the opportunity for
exploiting indirect selection between environments within the same gr
oup relative to environments in other groups. The objective in this st
udy was to identify groups of international environments, used by CIMM
YT in its international nursery program, which gave high indirect resp
onse to selection for grain yield in six Australian environments. Gene
rally the four classification strategies identified subsets of interna
tional environments for which selection gave a greater indirect respon
se than that for selection on average performance across all of the in
ternational environments (35% to 94% on average over all Australian en
vironments). Environmental classifications based on the standardised a
nd rank transformations were generally superior to those based on the
untransformed and coded transformations (46% on average over all Austr
alian environments). The magnitude of this advantage differed between
the Australian environments but was substantial for the two environmen
ts which expressed the greatest opportunity for exploiting indirect se
lection. These results have obvious and large implications for the use
of classification methodology to structure regional testing regimes f
or plant breeding programs.