Relationship among traits in individual environments
Under the main menu 4-Way, click Trait Association by Environment biplot - Associations among selected traits.
A trait selection form containing two list boxes will appear, allowing you select traits whose interrelationships are to be investigated.
GGEbiplot will first make a list of "relations" or 'Associations', i.e., pairs of selected traits. If N traits are selected, there will be N(N-1)/2 possible relations.
GGEbiplot will then generate a trait association by environment two-way table, which consists of correlation coefficients between each pair of traits in each of the environments.
A biplot based on this table, without any data transformation or centering, will appear. The following biplot is based on the 2003 Eastern oat screening trials, from which several agronomic traits were selected:
The biplot shows that
1) Seven relations (pairs of traits) (in blue) were significant at the 1% level in at least one of the five environments (in red). The relations with long vectors were stronger than those with shorter vectors. Thus, the relation between Days to Heading and Days to Maturity was strongest, as one would expect, followed by the relation between Days to Heading and Plant Height. These two relations are positive in all environments, as indicated by the angles between their vectors relative to those of the environments.
2) On the opposite, the relation between days to heading and yield seem to be negative in all environments.
3) Most interesting is the relation between plant height and yield, which was positive in HERBERT, NORMAND, and PRINCEWILLE, but negative in PEI and WOODSTOCK. This can be interpreted as that plant height was an important cause for the observed genotype by environment for oat yield.