Gamma-irradiated sodium alginate enhances growth, antioxidant defense, and citral-rich essential oil in Dracocephalum kotschyi

Gamma-irradiated sodium alginate (I-SA), a low-molecular-weight oligosaccharide elicitor, holds promise as a sustainable biostimulant for enhancing both yield and phytochemical quality in medicinal plants. In this study sodium alginated irradiated using a 60 Co gamma source and the dose-dependent effects of foliar-applied I-SA (0, 50, 100, 150, and 200 mg L −1 ) were investigated on growth, photosynthetic pigments, antioxidant systems, and essential oil composition in Dracocephalum kotschyi . Results revealed that I-SA significantly improved plant height (up to +32.6 %), leaf area (+72.7 %), and shoot dry weight (+52.0 %), with biomass accumulation maximized at 150–200 mg L −1 . Photosynthetic capacity was enhanced through a 63.3 % increase in total chlorophyll (at 100 mg L −1 ) and a 41.5 % rise in the chlorophyll-to-carotenoid ratio (at 200 mg L −1 ), indicating improved light utilization and reduced oxidative pressure. Concurrently, I-SA activated the antioxidant defense system: peroxidase activity increased by 82.0 %, anthocyanin content by 30.4 %, total phenolics by 16.0 %, and flavonoids by 22.1 %, culminating in a 12.6 % enhancement in total antioxidant activity at 150 mg L −1 . Notably, the essential oil profile shifted toward higher-value compounds, with citral (neral+geranial) rising to 39.91 % (vs. 36.0 % in control) and geranyl acetate peaking at 9.25 % under 150 mg L −1 treatment. Critically, 150 mg L −1 I-SA emerged as the optimal concentration, harmonizing maximal biomass, antioxidant capacity, and bioactive metabolite production. These findings highlight I-SA as a promising, eco-friendly biostimulant for medicinal plant cultivation. Future studies should explore its efficacy across diverse species and field conditions, and integrate physicochemical characterization to refine structure–activity relationships. • Irradiated sodium alginate (I-SA) elicits oligosaccharide signaling, enhancing photosynthesis and biomass production in Dracocephalum kotschyi. • I-SA integrates primary and secondary metabolism, upregulating photosynthetic pigments and inducing antioxidant enzymes (peroxidase) and phenolic compounds in D. kotschyi. • Foliar I-SA at 150 mg L⁻¹ optimally enhances biomass, total antioxidant capacity, and high-value bioactive metabolite accumulation in D. kotschyi. • I-SA enriches essential oil with oxygenated monoterpenes (citral, geranyl acetate), sustainably tailoring oil profiles for pharmaceutical and industrial applications.