Additive main effect and multiplicative interaction analysis of national turfgrass performance trials: I. Interpretation of genotype X environment interaction

The additive main effect and multiplicative interaction (AMMI) analysis has been shown to be effective in understanding complex genotype X environment (GE) interactions typical of National Turfgrass Evaluation Program (NTEP) variety trials. Interactions in such complex data sets are difficult to understand with ordinary analysis of variance (ANOVA). NTEP relies on ANOVA procedures (the basis of which is an additive model that does not sub-partition the interaction) for analysis of turf quality data. As a result, interactions have been largely ignored in turfgrass evaluation programs. The objective of this research was to target GE interactions with AMMI and NTEP data in order to understand why genotypes interact with environments. The 1990 Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.) variety trials were analyzed. Interaction patterns revealed by AMMI biplots indicated Kentucky bluegrass and perennial ryegrass genotypes are narrowly adapted because no genotype has superior performance in all environments (broad adaptability). In both trials, GE interactions could be explained in biologically meaningful terms in part by cultural intensity level (mowing height and nitrogen level) and disease resistance (leaf spot or brown patch). Some NTEP locations (Ames, IA; Beltsville, MD; East Lansing, MI; and Martinsville, NJ) were highly predictable in year-to-year interaction with genotypes (making cultivar recommendations more predictable), other locations were less predictable (Carbondale, IL; Lexington, KY; Post Falls, ID; and North Brunswick, NJ). NTEP locations were consistent in their interaction with genotypes across species. Environments interacted with genotypes according to a cultural intensity gradient (mowing height and fertilizer nitrogen). Climatic factors were not important in explaining GE interactions. Results suggest the potential to subdivide bluegrass and ryegrass growing regions into homogenous subregions (having similar interaction patterns and cultivar recommendations) that can be altered by cultural practices.