Jasmonic Acid Modulates the Morphological, Yield, and Phytochemical Responses of Roselle ( <i>Hibiscus sabdariffa</i> L.) Under Drought Stress

Roselle (<i>Hibiscus sabdariffa</i> L.) is a tropical and subtropical annual plant valued for its nutritional and therapeutic uses, including sour beverages, jams, and traditional medicines. Drought stress is a major abiotic factor limiting plant growth, yield, and quality. Jasmonic acid (JA), a key signaling molecule, plays a vital role in enhancing plant tolerance to environmental stress by supporting growth, nutrient uptake, photosynthesis, and biochemical defense. This study aimed to assess drought stress effects on roselle growth and productivity and evaluate JA's role in mitigating drought-induced damages. A field experiment was conducted with four irrigation levels (100%, 70%, 40%, and 25% field capacity (FC)) and foliar JA applications (0, 10, 30, and 60 mg L^-1). JA positively influenced morpho-physiological and yield traits. The tallest plants (233.67 cm and 231.67 cm) were recorded under 70% FC with 30 and 60 mg L^-1 JA. The highest biomass (27,060 kg/ha) was under full irrigation without JA. The greatest seed yield (1116.2 g/plant) and calyx yield (1081 kg/ha) occurred under 70% FC with 60 and 30 mg L^-1 JA, respectively. JA improved chlorophyll content under severe drought (25% FCs) by up to 28.87%, and phenol content under well-watered conditions by 22.73%. The highest ascorbic acid (19.04%) was observed under 25% FC + 10 mg L^-1 JA. These results highlight the multifaceted role of JA in enhancing roselle drought tolerance and productivity, particularly under moderate water-deficit conditions.