Sources of variation in spring wheat (Triticum aestivum L.) cultivars of the Western and Southern Cape. I. Milling and dough development characteristics
Approximately 90% of the annual wheat crop produced in the Republic of South Africa is milled into flour for bread-baking purposes. The percentage of flour extracted, as well as the dough development properties, determine the milling and dough mixing characteristics. In an increasingly deregulated market environment, these quality characteristics largely determine the price of the wheat. The ability of cultivars and localities to produce high quality wheat grain must, therefore, be classified. Seven spring wheat cultivars were grown at nine localities for the period 1992 to 1995. Similar production practices were followed at all localities. AMMI (Additive Main Effects and Multiplicative Interaction) analyses were used to describe the effect of cultivar, environment and their interaction on flour extraction yield, Falling Number, gluten, as well as Mixograph dough development time, peak height and band width. Environment was found to be the most important contributor to variance for all characteristics determined. No significant cultivar x environment interaction was found for flour extraction yield. Cultivar as a main effect contributed only 2.5% to the variation in flour extraction, while that of environment was 68.7%. Significant cultivar x environment interactions were found for Falling Number, gluten content, dough development time, peak height and band width. Interactions were particularly strong for cultivars such as Palmiet and Adam Tas in the case of Falling Number and gluten content, indicating a lack in stability in these properties. Nantes, SST 55 and to a lesser extent SST 16 and SST 66, showed considerable sensitivity with regard to dough development time, peak height and band width. Cultivar reaction over years may, therefore, vary considerably at the same locality. It is thus almost impossible to classify cultivars and localities according to these characteristics.