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Additive Main Effect and Multiplicative Interaction Analysis of National Turfgrass Performance Trials

I. Interpretation of Genotype x Environment Interaction

^a Dep. of Plant and Soil Sciences, 12F Stockbridge Hall, Univ. of Massachusetts, Amherst, MA 01003
^b Soil, Crop, and Atmospheric Sciences, 1021 Bradfield Hall, Cornell Univ., Ithaca, NY 14853

View larger version (29K): [in a new window]   Fig. 1. AMMI-1 plot of 69 environments (location-year combinations) from the 1990 NTEP Kentucky bluegrass variety trial and 60 environments from the 1990 perennial ryegrass variety trial. 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 environment. Displacement along the horizontal axis indicates differences in environment main effects. Dash lines show year-to-year variation within individual locations.

View larger version (35K): [in a new window]   Fig. 2. AMMI-1 plot of 125 genotypes from the 1990 NTEP Kentucky bluegrass variety trial identified by individual genotype and category type (from Murphy, 1994, see text for explanation). 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. Displacement along the horizontal axis indicates differences in genotype main effects.

View larger version (26K): [in a new window]   Fig. 3. AMMI-1 plot of 123 genotypes from the 1990 NTEP perennial ryegrass variety trial. 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. Displacement along the horizontal axis indicates differences in genotype main effects.

View larger version (37K): [in a new window]   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.