Interpretation of genotype X environment interactions for early maize hybrids over 12 years

Genotype X environment interaction was investigated for grain yield of earl y maize (Zea mays L.) hybrids. Data were obtained from the French Associati on Generale des Producteurs de Mais trial network and included 132 hybrids and 229 environments over 12 yr, following an unbalanced design. Analysis o f genotype X environment interaction was done for the 1-yr data sets, for t he two successive years data sets, and for the 12-yr data set. The magnitud e of genotype X environment interaction variance was equal to, or greater t han the genotypic variance. Interaction effect was modeled by factorial reg ression analysis using additional genotypic and environmental information. Genotypic covariates considered were the sum of growing day degrees (GDD) n ecessary from sowing to flowering and the GDD necessary from flowering to m aturity. Environmental covariates were the mean temperature from sowing to the 12 leaf stage, the mean temperature from the 12 leaf stage to the end o f the linear grain-filling stage, the water balance around flowering, and t he sum of solar radiation around flowering. These six covariates explained about 40% of the interaction effect in all analyses, with equal contributio n of genotypic variates (20%) and environmental variates (20%). Flowering e arliness of hybrids, water balance around flowering, and mean temperature f rom the 12 leaf stage to the end of the grain filling phase were determinan ts of genotype X environment interaction for grain yield in the considered area. A biological interpretation of the interaction was attempted through examination of the regression parameters.