Genotype x environment interaction and yield stability was evaluated for root yield for 28 sweetpotato breeding lines in South Africa using the Additive Main Effects and Multiplicative Interaction (AMMI) stability parameter. Genotype x environment interactions showed the inconsistency of the performance of the breeding lines over environments and seasons. The analysis of variance showed that the genotype x environment interaction were significant for root yield. The stability parameter used in this study identifies cultivar Monate as high yielding and stable across locations. The first two interaction principal component axes (IPCA) of the AMMI model accounted for 82.81% of the total genotype x environment interaction sum of squares for root yield. The AMMI biplot depicted the breeding lines on the bases of their adaptation patterns. Breeding lines Monate x 1999-9-4 and Khano x 1999-9-4 were found to be best adapted at Roodeplaat (A) environment while parental lines Ndou and 1999-9-4 as well as the breeding lines Monate x Khano, Khano x 1999-5-1 and 1999-9-4 x Khano were found to be the highest yielding at Fort Cox (D) environment. They were therefore recommended for cultivation in those environments.

Key words: Additive main effects and multiplicative interaction (AMMI) model, breeding lines, genotype by environment interaction, stability; sweet potato.