Alleviating Salt-Induced Effects in Stevia rebaudiana Via Exogenous Supply of Titanium Dioxide Nanoparticles and Putrescine

Salinity poses a serious challenge for stevia cultivation to meet growing demand. This study investigates protective supplements for stevia grown under saline conditions. Seedlings were subjected to titanium dioxide nanoparticles (0, 150, and 300 ppm), putrescine (0 and 1 mM), and salt (0, 75, and 150 mM) in a factorial design. Morphological traits (plant height, leaf dry and fresh weight), photosynthetic pigments (chlorophyll a, b, total), proline content, soluble and glycoside sugars (rebaudioside A and stevioside), and antioxidant enzyme activity (catalase and peroxidase) were measured. Higher salt concentrations (150 mM NaCl) reduced plant height, leaf dry and fresh weight, and chlorophyll but increased proline, soluble and glycoside sugars, and antioxidant enzyme activity. Foliar applications of putrescine (1 mM) and TiO2 nanoparticles (150 and 300 ppm) mitigated salt stress by improving growth and physiological properties. Simultaneous application of putrescine (1 mM) and TiO2 nanoparticles (300 ppm) was most effective at enhancing secondary metabolite production, important for the pharmaceutical industry. This study demonstrates protective roles of putrescine and TiO2 nanoparticles for stevia cultivation under saline conditions.