Combining ability, indirect and correlated response to selection for oil yield in sunflower (Helianthus annuus) under contrasting moisture environments

• Selection using secondary traits has potential to indirectly improve oil yield under drought conditions.
• Genetic correlation based on narrow sense heritability was studied in managed and random stress environments.
• The indirect selection efficiency for oil yield via stay green characteristic in sunflower is feasible.
• Type B genetic correlation was studied.
• Indirect selection for oil yield in the managed stress environments was as effective as direct selection for oil yield in the random stress environments.

Sunflower (Helianthus annuus L.) production in South Africa depends on natural rainfall which is variable and unpredictable, hence the need to develop drought tolerant sunflower genotypes to stabilise production under random stress environments. An exploratory research study was undertaken to determine the effectiveness of using moisture stress selection environments and three secondary traits, head diameter (HD), stem diameter (SD) and stay green canopy (SG) in developing drought tolerant sunflower cultivars with high oil yield (OY) in the presence of drought stress. A total of 84 testcross hybrids (TCHs) developed by crossing two testers to 42 female cytoplasmic male sterile (CMS) inbred lines were evaluated in nine environments for oil yield and other agronomic traits. The environments were classified as random drought stress environments (RSE), managed drought stress environments (MSE) and non-stress environments (NSE). Type A and type B genetic correlations based on broad sense heritability (H2) and narrow sense heritability (h2), respectively were estimated to quantify indirect selection efficiency. Type A genetic correlations indicated that SG had the potential to be used as a secondary trait to indirectly improve OY. The indirect selection efficiency (ISE) for OY via SG using genetic correlation based on H2 were 0.79, 0.82 and 0.78 in the RSE, MSE and NSE, respectively and genetic correlation based on h2 were 0.67, 0.98, and 0.93 in the RSE, MSE and NSE, respectively. In both cases, selection in the MSE had the highest ISE. Estimates of indirect selection based on type B genetic correlation indicated that indirect selection for OY in the MSE and NSE for the RSE was as effective as direct selection for OY in the RSE based on the additive genetic correlations of 0.96 obtained in both selection environments. Overall, the results from this exploratory study should inform the development of breeding strategies to improve the drought tolerance of sunflower cultivars grown in South Africa and associated environments.