Introduction: Medicinal plants, including Iranian borage (Echium amoenum Fisch. & Mey.), represent significant sources of therapeutic compounds and widely utilized in traditional medicine. The present study evaluates the effects of biofertilizers comprising arbuscular mycorrhizal fungi, plant growth-promoting rhizobacteria (PGPR), and seaweed extract on the quantitative and qualitative performance of Iranian borage. These biofertilizers enhance nutrient uptake, increase chlorophyll content, protein levels, and phytochemical concentrations, while also improving tolerance to environmental stresses, thereby promoting overall plant growth and quality in medicinal species. Given the environmental and health hazards associated with chemical fertilizers, the adoption of biofertilizers offers a sustainable alternative for the production of Iranian borage.

Materials and Methods: This field experiment was conducted in 2023 at an agricultural site in Kalaleh County, Golestan Province, Iran. The study employed a factorial arrangement based on a randomized complete block design with two factors, 20 treatment combinations, and three replications under field conditions. The first factor involved seed inoculation prior to planting at five levels: no inoculation (control, I₀), two species of arbuscular mycorrhizal fungi [Funneliformis mosseae (I₁) and Rhizophagus intraradices (I₂)], and two PGPR strains [Azotobacter chroococcum (I₃) and Azospirillum brasilense (I₄)]. The second factor consisted of foliar application of seaweed extract at four concentrations: 0 (S₀, control), 0.5 (S₁), 1 (S₂), and 2 (S₃) mL L⁻¹. Foliar sprays were applied starting at the 4–6 leaf stage in three stages at two-week intervals.

Results and Discussion: The results indicated that the interaction between seed inoculation and foliar application significantly affected all evaluated traits except plant height. Biofertilizer treatments led to significant improvements in morphological and physiological characteristics of Iranian borage. The combined application of Azotobacter chroococcum inoculation and 0.5 mL L⁻¹ seaweed extract (I₃S₁) significantly enhanced flower number and dry flower yield, increasing them from 808 flowers and 739.24 kg ha⁻¹ in the control treatment to 1268 flowers and 991 kg ha⁻¹, respectively. These improvements correspond to increases of 56.93% in flower number and 34.05% in dry flower yield compared to the control.Compared to the control, treatments involving Azospirillum brasilense and 1 mL L⁻¹ seaweed extract enhanced plant height by 10.58% and 39.93%, respectively. Foliar application of 1 mL L⁻¹ seaweed extract exerted the strongest influence on total phenolic, total flavonoid, anthocyanin, and soluble sugar contents. The highest total phenolic content (79.36 mg gallic acid equivalent g⁻¹ dry weight of flowers) and soluble sugars (30.37 mg g⁻¹ dry weight) were recorded under Azospirillum brasilense 1 mL L⁻¹ seaweed extract (I₄S₂). The maximum total flavonoid content (255.76 mg quercetin equivalent g⁻¹ dry weight) and anthocyanin content (6.1 mg quercetin equivalent g⁻¹ dry weight) were observed in Azotobacter chroococcum + 1 mL L⁻¹ seaweed extract (I₃S₂) and Rhizophagus intraradices + 1 mL L⁻¹ seaweed extract (I₂S₂), respectively. Furthermore, the highest mucilage content (10.95%) was achieved with I₄S₂. Plants treated with I₄S₁, I₂S₂, and I₃S₃ exhibited the highest nitrogen (1.43%), phosphorus (0.27%), and potassium (7.41 ppm) concentrations, respectively.

Conclusion: The findings of this study demonstrate that biofertilizers can substantially influence both quantitative and qualitative attributes of Iranian borage, although the magnitude and optimal application rates vary across traits. Based on the results, seed inoculation with mycorrhizal fungi—particularly PGPR strains—combined with foliar application of seaweed extract at 0.5–1 mL L⁻¹ is recommended to enhance flower yield and quality. Therefore, substituting chemical fertilizers with biofertilizers not only improves the agronomic and phytochemical performance of Iranian borage but also contributes to reduced environmental pollution and the advancement of sustainable agriculture.