Synergistic application of plant growth-promoting rhizobacteria and iron oxide nanoparticles enhances agro-physiological traits, antioxidant properties, and essential oil production in Satureja khuzistanica Jamzad: A sustainable biofortification approach

Satureja khuzistanica Jamzad, a medicinal plant endemic to Iran, struggles with micronutrient deficiencies, especially iron, in alkaline soils, limiting its growth and essential oil production. This study aimed to investigate the interaction impact of plant growth-promoting rhizobacteria (PGPR) ( Curtobacterium plantarum and Pseudomonas brassicacearum ) and Fe 2 O 3 in both nano and bulk forms, applied at concentrations of 0, 100, and 200 mg L −1 , on the yield, photosynthetic pigments, antioxidant activity, and essential oil of S. khuzistanica . The experiment was arranged as a factorial combination in a completely randomized design under greenhouse conditions. PGPR inoculation significantly improved root growth, absolute growth rate, leaf dry weight, relative water content, chlorophyll, flavonoid, essential oil content, yield, and iron content. Foliar application of Fe 2 O 3 enhanced the activity of phenylalanine ammonia lyase in the non-inoculated plants. Additionally, antioxidant activity was increased with the foliar spray of 200 mg L −1 Fe 2 O 3 , with notable improvements observed in the activities of catalase and ascorbate peroxidase. However, the combination of PGPR inoculation and Fe 2 O 3 significantly enhanced yield-related traits, relative water content, chlorophyll content, essential oil content, and Fe levels. Notably, the carvacrol percentage was markedly higher in non-inoculated plants treated with Fe 2 O 3 . The highest yield of essential oil was recorded with PGPR inoculation and 100 mg L −1 Fe 2 O 3 NPs. These findings provide the first evidence that integrating PGPR with Fe 2 O 3 NPs can sustainably enhance essential oil biosynthesis and agronomic traits in S. khuzistanica . This integrated biofortification strategy offers a promising, eco-friendly approach to improve growth and phytochemical quality in nutrient-deficient soils, with significant implications for the sustainable cultivation of high-value medicinal plants. • Combined PGPR and Fe 2 O 3 NPs improved yield, chlorophyll, RWC, and essential oil. • Fe 2 O 3 increased antioxidant enzymes, especially CAT and APX activity. • PGPR inoculation led to a significant increase in flavonoid levels. • Highest essential oil observed with PGPR and 100 mg/L Fe 2 O 3 NPs. • Fe 2 O 3 foliar application enhanced PAL activity in non-inoculated plants.