Benzoic acid versus salicylic acid efficacy in regulating growth, accumulation of secondary metabolites and NO3 content of Swiss chard (Beta vulgaris L. var. cicla)

Abstract Purpose Salicylic acid (SA) and benzoic acid (BA) are important phenolic regulators involved in plant growth and defense; however, their comparative roles in modulating growth and secondary metabolites production in leafy vegetables remain unclear. Therefore, this study aimed to investigate the influence of exogenous SA and BA on growth, mineral composition, and bioactive compound accumulation in Swiss chard ( Beta vulgaris L. var. cicla ). Methods Field experiments were conducted over two successive seasons of 2023/24 and 2024/25 to assess the influence of SA and BA on Swiss chard cv. Ruby Red. Plants were treated with SA and BA at 1, 2, and 3 mM, each alongside an untreated control. Treatments were arranged in a randomized complete block design with three replicates. Beside the agronomic attributes, photosynthetic pigments, total phenols, total flavonoids, total antioxidant activity, total indoles, anthocyanin, nitrate, and mineral content were assayed. Results Both SA and BA significantly improved growth parameters, mineral content, and secondary metabolites accumulation compared to the control. SA at 1 mM or BA 1 mM were the most effective treatments, showing the highest significant values of vegetative parameters, photosynthetic pigments, total phenolics, total flavonoids, total antioxidant activity, total indoles, anthocyanin, and mineral content. Further, BA 1 mM was the potent treatment for lowering leaf nitrate content, showing the lowest nitrate content, which was significantly lower than SA at 2 and 3 mM. Correlation analysis revealed strong positive relationships between growth parameters and secondary metabolites. Conclusion BA behaves influence similar to SA for enhancing leaves yield with higher efficacy in reducing nitrate content via enhancing the efficiency of photosynthetic pigments and regulating various secondary metabolites. Herein, BA at low concentration (1 mM) is a promising rate to be applied to obtain high yield with good quality.