Minimum detectable differences for cane yield, sucrose content and sugar yield among the Midlands and Coastal Short Cycle sugarcane breeding programmes in South Africa

Abstract

Minimum detectable differences (MDD) are the smallest difference between two genotypes that can be determined accurately at a given statistical significance threshold. The effect of genotype by environment interaction reduces accuracy of determining genetic values, increases MDD and reduces selection efficiency. The objective of this study was to determine the trends in MDD and their implications on cultivar development for the Midlands and Coastal Short Cycle sugarcane breeding programmes in South Africa. Data derived from 30 genotypes planted in six advanced cultivar trials in each programme were analysed to generate variance components used to estimate the MDD. The MDD decreased from planted to second ratoon crops, indicating lower efficiency associated with selecting in the planted crops. The lower MDD with a simulated fourth replication indicated the need to increase the number of replications in cultivar trials. The higher MDD for sugar yield compared with those for sucrose content suggested a low efficiency when selecting for sugar yield. Selecting for sugar yield using the components cane yield and sucrose content may increase efficiency. The Midlands programme was more efficient and produced smaller MDD than the Coastal Short Cycle programme. The MDD will be used to benchmark minimum gains at time of release.

Keywords: minimum detectable differences, selection efficiency, sugar yield, variance components