A PROCEDURE TO ASSESS THE RELATIVE MERIT OF CLASSIFICATION STRATEGIESFOR GROUPING ENVIRONMENTS TO ASSIST SELECTION IN PLANT-BREEDING REGIONAL EVALUATION TRIALS

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.