Sugarcane cultivar x time of harvest interactions in South Africa

The adaptability of new sugarcane (Saccharum spp.) cultivars to time of harvest (TOH), and reasons for yield variability between harvest times are currently unclear in South Africa. The objectives of this study were to evaluate the adaptability of commercial cultivars to TOH and to identify environmental factors responsible for differential cultivar responses. Two field trials consisting of the same set of seven commercial cultivars were established on adjacent fields and harvested either early (April/May) or late (October/November) in the season for six ratoons. Climatic data were summarized within individual growth stages (establishment, elongation, and ripening) and used to create environmental covariates for thermal time (TT), rainfall (RAIN), radiation (RAD), and a water stress index (WSI). Additive main effects and multiplicative interaction (AMMI) analysis, principal components analysis (PCA), factorial regression, and covariate-effect biplot analysis were used to analyse and interpret the genotype x environment (G x E) interaction for three commercial variables. The G x E interactions were significant (P