Document Type : Research Article
Authors
Department of Horticultural Sciences and Engineering, Faculty of Crop Sciences, Sari Agricultural Sciences and Natural Resources University, Sari, Iran
Abstract
Introduction
Basil (Ocimum basilicum L.), a warm-season herbaceous plant from the Lamiaceae family, is a valuable medicinal and culinary herb widely used in pharmaceutical, cosmetic, and food industries. Its aromatic leaves and mucilaginous seeds, beneficial for soothing sore throats, make it a significant crop in West Asia and the Middle East. As global populations grow, greenhouse and urban farming, such as vertical farming systems, have gained prominence to ensure year-round production (Massa, 2006). However, basil’s growth and productivity are often limited during low-light conditions, particularly in colder seasons. To address this, artificial lighting, particularly light-emitting diodes (LEDs), has emerged as a powerful tool due to their ability to deliver specific wavelengths, high photoelectric conversion efficiency, and optimal photosynthetically active radiation (PAR) efficiency (80–100%) (Darko et al., 2014). LEDs allow precise control over light quality and intensity, enhancing plant biomass and secondary metabolite production. Additionally, ascorbic acid, a potent antioxidant, plays a critical role in detoxifying reactive oxygen species (ROS) and improving plant growth under stress conditions (Shigeoka et al., 2002). Previous studies have shown that specific light spectra, particularly red and blue combinations, enhance terpenoid and phenolic content in basil (Rihan et al., 2020; Rafiei et al., 2023). Similarly, foliar application of ascorbic acid has been reported to improve growth and mitigate environmental stresses in various plants (Yadollahi et al., 2016; Esmailpour et al., 2023). This study investigates the combined effects of LED light spectra and ascorbic acid foliar application on the morphophysiological and phytochemical traits of basil under controlled conditions, aiming to optimize its production in low-light environments.
Materials and Methods
The experiment was conducted in the summer of 2024 at the Horticulture Laboratory of the University of Agricultural Sciences and Natural Resources, Sari, Iran. A split-plot design based on a randomized complete block with three replications was employed. The main factor consisted of four LED light treatments: three blue-to-red ratios (75:25 [BBBR], 50:50 [BBRR], 25:75 [BRRR]) and full-spectrum white light (FFFF). Red light was set at 660 nm, and blue light at 440 nm, with a photoperiod of 16 hours light and 8 hours darkness daily. The sub-factor included two levels of ascorbic acid foliar application (0.5 g.L-1 weekly and no application). Basil seeds were sown in plastic pots filled with a 1:1 mixture of perlite and cocopeat and fertilized using Hoagland’s solution via fertigation. Morphophysiological traits, including stem diameter, number of lateral branches, leaf count, fresh and dry shoot weight, root fresh and dry weight, and root volume, were measured. Phytochemical traits, such as antioxidant activity (DPPH method, measured at 517 nm), total phenolic content (Folin-Ciocalteu method, measured at 765 nm), and flavonoid content (aluminum chloride method, measured at 415 nm), were assessed using a spectrophotometer (UV-1800PC, Shimadzu, Japan). Data were analyzed using analysis of variance (ANOVA), and means were compared using appropriate statistical tests.
Results and Discussion
The results demonstrated that the red-blue (75:25) light treatment significantly enhanced several morphophysiological traits compared to full-spectrum light, increasing stem diameter by 8%, lateral branches by 26%, leaf count by 15%, fresh leaf weight by 39%, and dry shoot weight by 25%. Foliar application of ascorbic acid further amplified these traits, with increases of 23%, 21%, 20%, 44%, and 31%, respectively. The combination of red-blue (75:25) light and ascorbic acid resulted in the highest stem height, root dry weight, and root volume, indicating a synergistic effect. These findings align with previous research showing that red light promotes stem elongation and biomass accumulation through gibberellin synthesis, while blue light regulates cellular expansion via cryptochromes (Hosseini et al., 2019; Kaiser et al., 2019). Ascorbic acid likely enhanced growth by acting as a coenzyme in photosynthesis and hormone biosynthesis, increasing carbohydrate production and nutrient uptake (Barkosky and Einhellig, 2003). For phytochemical traits, the red-blue (50:50) light without ascorbic acid yielded the highest antioxidant activity, suggesting that balanced light spectra stimulate defense mechanisms. The red-blue (75:25) light increased phenolic content by 12% and flavonoid content by 28% compared to full-spectrum light, consistent with studies showing that blue light enhances phenylpropanoid biosynthesis via phenylalanine ammonia-lyase (PAL) activation (Rafiei et al., 2023). However, ascorbic acid did not significantly increase flavonoid content, possibly due to metabolic saturation or suppression of defense responses at high antioxidant levels (Azoz et al., 2016). These results highlight the importance of tailored light spectra and nutritional interventions for optimizing basil’s growth and secondary metabolite production.
Conclusion
This study confirms that LED light spectra, particularly the red-blue (75:25) combination, significantly improve basil’s morphophysiological traits, including stem diameter, leaf count, and biomass, under low-light conditions. Foliar application of ascorbic acid enhances these effects, promoting root development and overall plant growth. While specific light spectra alone can boost antioxidant activity and phenolic content, ascorbic acid’s influence is more pronounced on growth than on flavonoid accumulation. These findings provide a practical framework for optimizing basil production in controlled environments, such as greenhouses and vertical farms, by integrating light quality management with ascorbic acid supplementation. This approach offers a cost-effective strategy to enhance both the quantity and quality of basil, supporting sustainable agricultural practices.
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