METHODS FOR EVALUATING GENOTYPE-ENVIRONMENT INTERACTIONS ILLUSTRATED BY LAYING HENS

The relative efficiency of several methods of studying genotype-enviro nment interactions has been illustrated, considering some performance traits In laying hens as a model. The comparison involved methods of c lassifying, detecting the existence, and estimating the magnitude of g enotype-environment interactions. The environments consisted of warm ( 32 degrees C) and temperate (20 degrees C) climatic conditions. Classi fication and qualitative description of interactions is useful when ve ry few genotypes and environments are involved. The illustration with an example suggested that a classification based on comparison of rela tive magnitudes of average genotypic, environmental and interaction ef fects would be most meaningful. The interactions carry greater signifi cance if they exceed the average genotypic effects. A factorial analys is of variance followed by an F-test can be useful in detecting the ex istence of interactions, but statistical significance should not be ov eremphasized for biological relevance. Invariably, the magnitude of in teractions muse be estimated to derive useful conclusions. The seven m ethods of estimating this correlation mainly involved principles of in traclass correlation, rank correlation and product-moment correlation. An analysis of data revealed that the intraclass correlation methods, in general, yielded higher estimates compared to the rest of the meth ods. Among them, the formula given by DICKERSON (1962) was found more appropriate in mixed-model analysts with unbalanced data while the met hod given be YAMADA (1962) resulted in negative estimates when the int eraction variance was large. The least reliable among the methods were estimations directly utilizing the mean squares from factorial analys is of variance as suggested by ROBERTSON (1959). Rank correlations wer e similar for phenotypic as well as genetic rankings and also coincide d to some extent with the correlation among the breeding values, revea ling distinct changes in ranks of genotypes in those traits where the interactions were larger. Product-moment correlations between the bree ding values of sires in the two environments should be the most reliab le and suitable for predicting selection response when the sires are s elected in one environment and their progeny is required to perform un der different conditions. Ho wever, their expectations were lower than 1, depending upon the genetic foundation of the traits and effective progeny size.