INCORPORATING ENVIRONMENTAL INFORMATION IN AN ANALYSIS OF GENOTYPE BYENVIRONMENT INTERACTION FOR SEED YIELD IN PERENNIAL RYEGRASS

Seed yield in perennial ryegrass was analysed for cultivar by environm ent interaction. Nine cultivars were evaluated in 12 trials at two loc ations over a 3-year period. Earlier attempts to describe the signific ant cultivar by environment interaction using a regression on the envi ronmental mean or relationships with year, soil type, harvest method, or crop age, were unsuccessful. In this paper, therefore, meteorologic al data were introduced as explanatory variables. Three types of analy sis were used. First, residuals from the cultivar by environment two-w ay table corrected for main effects were regressed on the explanatory variables for each cultivar separately. Secondly, the explanatory vari ables were used as concomitant variables for the environmental factor in a two-way analysis of variance of genotypes by environments. Finall y, the matrix of residuals from additivity was subjected to a singular value decomposition, after which environmental scores were related to values of the explanatory variables using regression and a recently d eveloped method to calculate confidence intervals for scores. All meth ods led to comparable conclusions about the importance of different va riables in the interaction. Of equal importance were minimum temperatu re in the period before ear emergence, temperature sum in the period f rom the beginning of anthesis until peak anthesis, and mean and maximu m temperature in the period from the end of anthesis until harvest. Th e major component of interaction was identified as a contrast between early and late cultivars. A minor component was due to cultivars that performed relatively well in the worst environment and relatively badl y in the best environment. The usefulness of so-called AMMI models is discussed and compared with that of the more traditional regression on the environmental mean model.