Sources of variation for yield, protein content and hectolitre mass of spring wheat (Triticum aestivum L.) cultivars of the Western and Southern Cape
In the Western and Southern Cape the quality of wheat varies annually due to variable climatic conditions. This holds a commercial risk to the milling and baking industries in delivering the refined products to their respective clients. It is, therefore, important to classify cultivars and localities according to their ability to produce high quality bread wheat grain. In this study, similar production techniques were used to grow seven spring wheat cultivars at nine localities for the period 1992 to 1995. AMMI analyses were used to describe the effect of genotype, environment and their interaction on grain yield, kernel protein content and hectolitre mass. Environment was found to be by far the most important parameter of variance. No significant genotype x environment interaction was found for grain yield. Although cultivars differed in their yield potential, genotype as a main effect contributed only 1.3% to the variation in yield when compared to 90.7% for environment. Significant genotype x environment interactions were found for grain protein content and hectolitre mass. Cultivars such as Palmiet, Nantes, SST16 and to a lesser extent Adam Tas, showed considerable sensitivity to both high and low protein areas, indicating a lack in stability for this parameter. Annual variation in rainfall during the grain filling period dominated environmental variation for hectolitre mass, making it almost impossible to classify cultivars and regions according to their ability to produce high hectolitre mass.