Breeding investigations into the gene action and agronomic performance of sunflower traits based on F1 top-cross hybrids

Information on the performance and gene action of sunflower traits is still scarce in southern Africa despite the crop’s increasing importance and the growing demand for adapted cultivars. To generate this information, 30 malesterile lines were cross-bred to a restorer line generating 30 experimental hybrids. The hybrids and three check varieties were evaluated in South Africa, Zambia and Zimbabwe. Data was analysed using REML procedure in Gen- Stat(R). Significant differences (P is less than 0.05) were observed for grain yield traits, oil content and days to 50% flowering. Grain yield ranged between 1700 kg/ha and 4278 kg/ha, 1000-seeds weight between 59.4 g and 89.3 g, oil content between 36.6% and 44.6%, and days to 50% flowering between 55.5 and 68.0 for the hybrids but going up to 70 for the control varieties. Five hybrids were ranked above the highest performing check variety for grain yield. Two hybrids, HV9120 and HV9132, significantly outperformed the highest check variety by up to 19.6% and the lowest check variety by up to 91.6%. Oil content showed similar trends with eight hybrids having up to 6.8% yield advantage over the highest check variety and 19.3% over the lowest check variety. The high yields were attributed to heterosis and indicated the high potential for grain yield and oil content from the current germplasm set. The presence of high yielding hybrids with shorter days to 50% flowering, such as HV9132, HV9127, HV9128 and HV9135, showed that it was possible to breed for the short growing season, characteristics of most southern African areas, without compromising grain yield. General combining ability (GCA) effects were significant for all the traits indicating the importance of additive gene action for the traits. Parental lines KP1235, KP1304 and KP1290 that showed desirable GCA effects for at least three of the important traits, were selected for inclusion in the breeding programme for cultivars adapted to the region.