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Abstract

Salinity is one of the common environmental stressors that negatively affect the plant growth, physiological processes and bioactive compounds production in medicinal and ornamental plants. Tagetes erecta L. (African marigold) is an important medicinal and ornamental plant, recognized for its antioxidant, antimicrobial and pharmaceutical activities primarily due to its phenolic and flavonoid constituents. The present study investigated the effect of salinity stress (0 and 60 mM NaCl) and foliar application of salicylic acid (SA; 0, 0.01, 0.05 and 0.10 mM) on growth, flowering, biochemical traits, antioxidant activity and antibacterial properties of T. erecta. Salinity significantly reduced vegetative growth, flowering performance, carbohydrate accumulation, mineral nutrient content, and chlorophyll concentration, but increased proline accumulation and phenolic biosynthesis. Foliar application of SA alleviated salinity-induced adverse effects and improved plant performance under saline and non-saline conditions. The 0.05 mM SA treatment showed the maximum plant height, biomass production, flower yield, carbohydrate content, potassium and calcium concentrations, total phenolics, DPPH radical scavenging activity, and β-carotene–linoleic acid antioxidant activity. Moreover, leaf extracts of plants treated with 60 mM NaCl and 0.05 mM SA exhibited the highest antibacterial activity against Gram-positive and Gram-negative bacteria, with the lowest MIC and MBC values. The results showed that moderate salinity could induce the accumulation of bioactive compounds in T. erecta, and exogenous SA further improved stress tolerance and medicinal value by improving antioxidant capacity, phenolic metabolism and antimicrobial activity. The present results highlight the potential use of SA as an efficient biostimulant to improve the commercial and pharmaceutical quality of marigold grown under saline conditions

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