Fig. 4. AMMI-1 biplot showing both genotype and environment (location-year combinations) from the 1990 NTEP Kentucky bluegrass and perennial ryegrass variety trials. IAS-1 = interaction scores for the first interaction axis, IAS-1 scores close to zero indicate little or no interaction (IAS-1 scale in units equivalent to the square root of turfgrass quality). Displacement along the vertical axis indicates interaction differences between genotype or environment. Displacement along the horizontal axis indicates differences in genotype or environment main effects. Estimate of the GE interaction for a given genotype x environment combination is the product of their corresponding IAS-1 scores.