Application of silicon coupled with sulfate improve the drought tolerance in sunflower via modulating the morpho-physiological and antioxidants defense mechanisms

Abstract Background ​Sunflower (Helianthus annuus L.) is one of the main oilseed crops as an essential dietary component used for human and animal feed. Due to changing climate scenarios, severe drought conditions adversely affect growth and productivity of sunflower. The current study was planned to investigate the potential of sole and combined application of silicon (Si) and sulfate (SO4) to improve sunflowers' morpho-physiological, yield and yield traits under water deficit conditions. Methods There were two factors in the experimental treatments; i) two levels of irrigation regimes, 80% water holding capacity (WHC) and 40% WHC and ii) control (Ck), water spray, 4.0 mM Si, 4.0 mM SO4 and Si + SO4 (4.0 mM + 4.0 mM). Drought stress was imposed at the 50% heading stage of sunflower. Results Drought stress reduced leaf chlorophyll pigments and relative water contents. In contrast, it diminished the growth and production of sunflower by reducing plant height, stem girth, head diameter, leaf area index, numbers of achene per head, 100-achene weight, biological yield and achene yield per plant. Results of the study indicated that Chl a, b, and a + b and relative water contents significantly increased with sole and combined application of Si and SO4 under drought stress condition. Moreover; remarkably improved antioxidant activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) was recorded along with the accumulation of soluble proline and protein with the combined application of Si and SO4 under drought stress. The combined application of Si and SO4 improved the sunflower growth by enhancing plant height (17%), stem girth (17.66%), head diameter (18.15%), leaf area index (17.80%), number of achene per head (19.46%), 100- achene weight (10.70%), biological yield (17.12%) and achene yield per plant (17.21%). Conclusions The combined application of Si and SO4 is the best option to alleviate the adversities of drought stress for the growth and development of sunflower.