Multi Environmental Trials

Abstract

Most field tests for plant breeding are replicated across different environments to measure the performance of breeding stocks across a range of environmental conditions to which a cultivar might be exposed. Multi-environment trials provide information about the adaptability of genotypes to specific environments or to sets of environments. The variance-covariance structures introduced in preceding chapters can be used to model genotype-by-environment interactions in multi-environmental trials. The number of parameters required to fit fully specified multi-environment trial models increases faster than the number of environments, so more parsimonious models are preferred when the number of environments is large. In this chapter we compare an unstructured matrix that involves separate parameters for genetic variance within each environment and for genetic correlations between each pair of environments to more parsimonious models, such as factor analytic structures, which require fewer parameters. Factor analytical structures can often efficiently capture the genotype-by-environment patterns without requiring extraordinary model complexity.