Family x environment and genotype x environment interactions for sugarcane across two contrasting marginal environments in Mauritius

Land resources are scarce in Mauritius and to fulfil the export quota sugarcane (Saccharum hybrids has to be grown in marginal areas which are not conducive to optimal growth. In order to increase overall productivity there is a need to breed and select sugarcane varieties specifically adapted to the extremely dry and extremely wet areas. In this study, 154 genotypes representing four families were planted in a randomized complete block design at two sites. The genotypes were replicated at the two sites and evaluated in the plant cane and first ratoon crops. Family x environment and genotype x environment interactions were determined using the mixed model analysis of variance. Significant differences between families, genotypes and environments were found in stalk height, stalk diameter, industrial recoverable sucrose % cane (IRSC) and cane yield per hectare in tonnes (TCH). The genotype x environment interaction was significant for stalk height, stalk number, stalk diameter, sucrose content, TCH, tonnes sugar per hectare (TSH) and kilobrix (parameter used for selection in the preliminary phase of the selection programme at the Mauritius Sugar Industry Research Institute) in both plant cane and first ratoon crops indicating that the relative performance of the genotypes is not consistent across the environments for these characters. The family x environment interaction was found to be significant for cane and sugar yields whereas it was not significant for field Brix in either the plant cane or the ratoon crops. This showed that, for the parameter Brix, the relative performance of the families is similar in both environments and there is no need to replicate in more than one environment. The environmental sensitivities measured with respect to sugar yield showed that families and genotypes with nearly equal means over all environments displayed inconsistent performances. Differences in the sensitivities of the different families and genotypes were observed and some of the family x environment and genotype x environment interactions could be ascribed to them. The results also suggest that mass selection could be more effective than family selection and selection for each specific environment is advisable.