Foliar application of chitosan and nano-magnesium fertilizers influence on seed yield, oil content, photosynthetic pigments, antioxidant enzyme activities of sesame (Sesamum indicum L.) under water-limited conditions

Abstract

Applying elicitors and nano-fertilizer has been recommended to enhance the growth and yield of secondary metabolites in herbs and medicinal plants under water-limited stress. However, less information is available on the effects of chitosan and nano-magnesium fertilizers on sesame seed yield, oil content, and physiological traits in the presence of nano-magnesium chelate (nano-Mg) under water-limited supply. In this regard, field experiments as a split-factorial experiment was performed based on randomized blocks in three replicates in Varamin city, south of Tehran, Iran, during 2015-2016 to evaluate the impact of chitosan and nano-Mg on physiological, seed, and oil traits of sesame. Irrigation cut-off based on BBCH scale was considered as the main factor including normal irrigation (I₁), irrigation cut-off in 75 (I₂), and 65 BBCH (I₃) stages. Secondary factors as the subplot included ‘Oltan’ (C1) and ‘Dashtestan-2’ (C2) sesame cultivars, and foliar application of nano-Mg (application and non-application) and chitosan (control (CH1), foliar application of 4.8 g L^-1 in 65 BBCH (CH2), and 6.4 g L^-1 in 75 BBCH stages (CH3)). Further, free proline content, total sugars, the activity of antioxidant enzymes including catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1), and ascorbate peroxidase (APX, EC 1.11.1.11), photosynthetic pigments content, seed yield, and oil content were evaluated in the next stage. Based on the results, irrigation cut-off in 65 BBCH stage (flowering) significantly increased free proline content, total sugars, and the activity of antioxidant enzymes, CAT, POD, and APX. However, chlorophyll a, b, and total contents, seed yield, oil percentage, and yield decreased under water stress. ‘Dashtestan-2’ cultivar had the highest seed yield and oil content, and more tolerant cultivar under water-limited stress. Interestingly, the production of proline content and total sugars increased while the activity of antioxidant enzymes, CAT, POD, and APX decreased under application of nano-Mg and CH2, which influenced both sesame response and seed attributes. As a result, the production of some physiological traits in sesame cultivars may be regulated by adjusting the irrigating practices. Finally, the co-application of nano-Mg and CH2 increased the seed yield and oil content of sesame under limited water supply in the arid and semi-arid region.