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Abstract

Water stress is one of the main environmental factors that limit the productivity and medicinal quality of ornamental and medicinal plants. The present research evaluated the effect of long term irrigation intervals and salicylic acid (SA) application on growth, biochemical composition, antioxidant activity and antimicrobial potential of Catharanthus roseus (L.) G. Don. (Apocynaceae). Plants were watered at two intervals namely 2 days (2DWI) and 6 days (6DWI) along with foliar application of SA at different concentration (0, 0.01, 0.05 and 0.10 mM). The prolonged irrigation interval significantly reduced vegetative growth and flowering attributes such as leaf number, leaf area, plant dry weight, plant height and flower number per plant. On the other hand, drought stress led to increased total carbohydrates, proline accumulation, antioxidant activity and total phenolic content. Activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) were also improved under water-stress conditions. Foliar application of SA significantly alleviated the negative impact of drought stress and improved all growth parameters studied in the two irrigation regimes. The highest concentration of SA (0.10 mM) showed the most favourable improvements in vegetative growth, chlorophyll content and flower production. Furthermore, SA treatment increased antioxidant capacity by decreasing DPPH and β-carotene-linoleic acid IC50 values and increasing phenolic accumulation. Leaf extracts of C. roseus showed considerable antibacterial and antifungal activities, which were improved further with longer irrigation intervals and SA application. In general, the strongest antimicrobial activity was observed under 6DWI combined with 0.10 mM SA. The results indicate that controlled water stress enhanced the accumulation of bioactive compounds in C. roseus. Exogenous SA application could effectively alleviate the inhibition of growth and improve the physiological performance, antioxidant defence and medicinal value under drought stress. SA application could serve as a sustainable agronomic strategy for maintaining medicinal plant productivity and improving phytochemical quality under water-limited conditions, thereby supporting sustainable cultivation practices in arid and semi-arid regions

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