GENOTYPE-X-ENVIRONMENT INFLUENCE ON CASSAVA PERFORMANCE

To study the relative influence of genotype, environment and genotype X environment (g X e) effects on six agronomic traits of importance, f ifteen morphologically diverse cassava genotypes were tested in 12 env ironments, comprising six locations over two seasons per location, The locations were representative of three major agro-ecological zones in Peninsular Malaysia, as well as of two major soil types: mineral and peat. Fresh root yield, commercial root number and root cyanide conten t were not associated with soil type, but high yield on peat might be related to high rainfall. Feat environments seemed to favour high harv est index except when there was a prolonged drier season, On mineral s oils, high soil P and K contents may explain high harvest indices. Low rainfall prior to harvest may increase root cyanide content. Root sta rch content may be associated with high pH on mineral soils. Dry matte r content in the roots was greatest when soil pH exceeded 4.6, except when rainfall was heavy just prior to harvest. Genotype effects were s trongest in controlling root cyanide content, harvest index and root d ry matter content, while environment was the main source of variation for commercial root number and fresh root yield. Location X season eff ects were the most prominent of the environment components. Season had a significant effect only in the expression of root dry matter conten t, but was nevertheless smaller in magnitude than the genotype effect. Genotype X environment (g X e) effects were significant for fresh roo t yield, commercial root number, harvest index, and for root starch an d cyanide contents. Except for fresh root yield and commercial root nu mber, these effects were smaller than the genotype effect. Only root c yanide content showed a linear g X e relationship with environment.