Evaluation of varieties: Genotypes, environments and genotype-environment interactions

One of the popular models for variety performance evaluation is the Additive Main Effects and Multiplicative Interaction (AMMI) model. The observed data of a trait such as yield recorded for ith genotype tested in jth environment is analyzed by the model:(main effect of ith genotype)+(main effect of jth environment)+(sum of multiplicative terms of genotypic and environmental effects). Another model used in the present study is the PATH model which uses the developmental sequence of yield components [no. stems/plant (X) to no. tubers/stem (Y) to tuber size (Z)] for the formation of yield (W=XYZ) to formulate the model composed of (main effect of ith genotype)+(three multiplicative terms of genotypic and environmental effects). Data of yield and yield components were collected from a group of genotypes tested over a series of replicated trials conducted in New Brunswick in 1998 and 1999. Analyses were carried out by both AMMI and PATH models. Both models describe the differential responses of genotypes to the environment effects. The PATH model further revealed the patterns of plasticity of the genotype to the environments during growth.