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Abstract

The present study investigated the effect of saline stress and salicylic acid (SA) treatment on growth, flowering, biochemical attributes, antioxidant properties, and antibacterial activity of Calendula officinalis. Plants were treated under two salinity levels (0 and 60 mM NaCl) and four SA concentrations (0, 0.01, 0.05, and 0.10 mM). Salinity caused a significant reduction in vegetative growth, flowering performance, carbohydrate accumulation, mineral content, and chlorophyll concentration. Salt-stressed plants showed reduced plant height, biomass production, flower yield, potassium, calcium, and total carbohydrate contents as compared to non-stressed plants. Conversely, salinity increased proline accumulation, total phenolic content, antioxidant activity, and antibacterial properties of leaf extracts. Foliar application of SA decreased the adverse effects of salinity and improved the plant performance under saline and non-saline conditions. Among the concentrations used, 0.05 mM SA produced the highest increases in growth, flower production, antioxidant activity, and biochemical constituents. SA application enhanced total phenolic content, DPPH scavenging activity, and the inhibition of β-carotene-linoleic acid and maintained higher chlorophyll and mineral contents under salinity. The strongest antibacterial activity of leaf extracts against the tested bacterial strains was observed under salinity and 0.05 mM SA treatments. Gram-positive bacteria were more sensitive to the extracts than Gram-negative bacteria. The results demonstrated that exogenous SA could alleviate the salt stress and improve the medicinal quality and biological activity of C. officinalis under saline conditions

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