Purpose: This study aimed to examine the effects of the exogenous application of ascorbic acid (ASA) on the growth and pigment content of Calendula officinalis L. flower heads under salinity stress. Methods: A pot experiment performed as a 5 × 3 × 4 factorial based on a completely randomized design (CRD) to evaluate the response of marigold to ASA foliar application (0, 3, and 6 mM) under five salinity levels (0, 25, 50, 75, and 100 mM NaCl). ASA foliar application on plant growth parameters, carotenoid, total phenolic, total flavonoids, flavonol content, the antioxidant activity of the flower heads, proline content of leaves, cell membrane injury, and water content under salinity stress investigated. Results: The results indicated that ASA and NaCl levels had significant effects on all studied characteristics, and ASA application was practical to mitigate the adverse effect of NaCl stress. By increasing NaCl levels, the growth, dry matter, carotenoid, flavonoid, and flavonol contents of marigold flowers were decreased; these characteristics increased by ASA application (especially 6 mM). While by increasing NaCl, the proline and total phenolic contents, antioxidant activity, and cell membrane injury increased, and these traits decreased by using ASA. At the highest NaCl concentration (100 mM), application of 6 mM ASA increased total dry biomass, dry matter of flower, carotenoid, total phenolic, and flavonoid content of the flower by 51.11%, 2.71%, 1.63%, 31.5%, and 1.65%, respectively. Whereas by using 6 mM ASA at 100 mM NaCl concentration, antioxidant activity, proline content, and cell membrane injury decreased by 2.51%, 33.34%, and 6.17%, respectively. Therefore, using 6 mM, ASA had more effective influences than 3 mM. Conclusion: Foliar ASA spraying enhanced secondary metabolites of marigold. Also, ASA application helped the plants resistant to salt stress by several mechanisms, including increasing proline and cell membrane stability.

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