Combining ability effects of some spring wheat cultivars at two different temperature levels

Yield losses due to high temperatures in the wheat growing season is a serious problem in South Africa. The aim of this study was to determine how the expression of general combining ability (GCA) and specific combining ability (SCA) was influenced by high temperatures in five commercial spring wheats. A full diallel cross was made with five spring wheat cultivars. One set of parents and their F1 hybrid progenies were grown under high temperatures and a second set under control temperatures. Additive gene action was predominant for all characteristics measured at both temperature levels. Additive gene action was significantly lower at the higher temperature conditions for most characteristics. Parents with the highest GCA effects at one set of temperatures tended to have the highest GCA effects for the other temperature level as well. SCA effects were expressed significantly different at the higher temperatures. High SCA effects for a characteristic at one temperature level were often paralleled by low or...