Development of urtica dioica-functionalized tragacanth hydrogels for improving early growth, physiological performance, and drought tolerance in basil (Ocimum basilicum)

Drought stress is one of the major environmental factors limiting plant growth and productivity. In this study, tragacanth-based hydrogels functionalized with Urtica dioica extract (p(Tragacanth-co-Urtica)) were synthesized and evaluated for their potential to improve drought tolerance in basil ( Ocimum basilicum L.) under different irrigation regimes (100%, 60%, and 40% of full irrigation). Plant growth parameters, physiological traits, antioxidant enzyme activities (catalase, superoxide dismutase, and ascorbate peroxidase), non-enzymatic antioxidants (total phenolic content and FRAP), and oxidative stress markers (malondialdehyde and proline) were analyzed. In addition, hydrogel swelling behavior, FTIR characteristics, and multivariate relationships among biochemical parameters were investigated. The developed p(Tragacanth-co-Urtica) hydrogel exhibited enhanced swelling stability and water-retention properties compared with the unmodified hydrogel. Drought stress significantly reduced growth and altered biochemical responses in basil plants, whereas hydrogel application mitigated these adverse effects. In particular, p(Tragacanth-co-Urtica) improved shoot and root growth, reduced oxidative damage, and promoted more balanced antioxidant responses under deficit-irrigation conditions. Principal component analysis explained 74.7% of the total variance and revealed treatment-dependent differences in biochemical responses. A positive but statistically non-significant relationship was observed between total phenolic content and FRAP activity ( r = 0.50, p = 0.167). Overall, the results demonstrate that functionalization of tragacanth-based hydrogels with Urtica dioica extract provides a multifunctional bio-based material that combines water-retention capacity with biologically relevant plant-supporting effects. The developed hydrogel showed promise for improving early-stage growth and physiological performance of basil under water-limited conditions.