GENOTYPE × ENVIRONMENT INTERACTION IN CACTUS PEAR (OPUNTIA SPP.), ADDITIVE MAIN EFFECTS AND MULTIPLICATIVE INTERACTION ANALYSIS OF FRUIT YIELD

More than 70 cactus pear cultivars are available in South Africa, but few are planted for commercial fruit production. Empirical cultivar recommendations are available for cactus pear growing in the diverse agro-climatic areas of the country. Regular reports of good vegetative growth but poor fruiting in some cultivars indicate possible Genotype x Environment (GxE) interaction. Eleven cultivars with commercial potential were planted in three agro-climatic zones of Limpopo Province to determine GxE interaction for fruit yield. This information will assist in identifying adapted and superior cultivars for future cultivation and breeding, and to determine if the Additive Main Effects and Multiplicative Interaction (AMMI) statistical model is suitable to elucidate the multivariate response of cactus pear genotypes to different environments. Highly significant differences (P< 0.001) were found for genotype, environment and GxE interaction. These results indicate a strong influence of environment on fruit yield of cactus pear genotypes. Different genotypes, and specifically different species, tend to be adapted to different agro-climatic zones. Plant morphology was not useful to predict environmental adaptation. The highest fruit yields were obtained at 1100 m.a.s.l., an area characterized by warm summers and cool winters. Broad genotype adaptation was found in ‘Zastron’, and to a lesser extent ‘Nudosa’ and ‘Algerian’, while all others showed strong GxE interaction. The AMMI model was useful to summarize relationships between genotypes and environments as well as to assess yield stability, allowing ranking of genotypes for each environment.