Magnesium Nanoparticles Improve Grain Yield, Oil Percentage, Physiological, and Biochemical Traits of Sunflower (Helianthus annuus L.) under Drought Stress

Sunflower (Helianthus annuus L.) is an oil grain crop of subtropical and tropical areas with arid to semi-arid climate and its production is affected by drought at the grain filling and flowering stages. Given the key role of Magnesium (Mg) in many key metabolic processes, it seems that Mg Nanoparticles (NPs) can improve the sunflower performance in drought stress. This study was carried out as a split-split plot in a randomized complete block design with three factors, including irrigation regimes (drought and normal), cultivars (Barzagar, Farokh, Ghasem, and Shams), and Mg NPs application (0.25 g L-1), and time (flowering and grain filling stages), in three replications in the field during 2017-19 seasons. Several physio-biochemical traits along with grain yield and oil percentage were measured. Based on the results, Mg NPs spraying increased the relative water content, chlorophyll and carotenoid, soluble carbohydrates, and antioxidant enzymes activity under drought. Moreover, Mg NPs spraying decreased electrolyte leakage and malondialdehyde content in the stressed plants and slightly increased grain yield and oil percentage. Overall, our findings suggest that Mg NPs can improve sunflower performance under drought by several mechanisms including improved antioxidant system, enhanced photosynthetic pigments, and increased primary metabolites.