Refereed Paper Components of Genotype by Environment Interaction among Sasri Regional Breeding and Selection Programmes and Their Implications

Genotype by environment interaction (GxE) influences and complicates the selection of superior genotypes in trials by confounding the determination of true genetic values. Trials therefore need to be planted over several locations and seasons. The South African Sugarcane Research Institute (SASRI) operates seven regional breeding programmes representing the major agro-climatic regions of the sugar belt. The objective of this study was to determine the variance components of GxE and evaluate their relative importance and implications in the breeding programmes. Data were analysed using the mixed procedure of the Statistical Analysis System (SAS) to estimate variance components and test their significance. There was significant genotype by location in the irrigated and coastal long cycle than the coastal short cycle and Midlands programmes, indicating the importance of identifying and characterising sites used for variety trials. The genotype by crop-year variance component was more significant for the rainfed than irrigated programmes indicating that breeding and selecting for ratooning ability was critical in rainfed regions. Genotype by location by crop-year interaction was more significant for yield than sucrose content, highlighting the complexity associated with breeding and selecting for yield. The variance components also showed that the coastal long cycle and hinterland programmes were the most complex and were generally characterised by large GxE. Programmes with crop cycles of more than 12 months produced more complex variance components indicating the difficulty of making genetic gains.