Effect of Red-to-Blue Supplemental Light Ratio on Flower Biomass, Essential Oil Production, and Anti-Inflammatory Activity in Chrysanthemum indicum L.

This study evaluated the effects of supplemental LED lighting on the photomorphogenesis and phytochemical characteristics of flowers of Chrysanthemum indicum L. Four lighting treatments were applied, including three red and blue LED spectral ratios (30:70, 55:45, and 78:22) under 6 h of daily supplemental lighting (F2–F4) and a natural sunlight control (F1). Supplemental photosynthetic photon flux density was maintained at 100 µmol·m−2·s−1. The highest average flower number (196.2 flowers·plant−1) was obtained under F1, whereas the greatest average fresh flower biomass (55.5 g·plant−1), dry flower biomass (7.4 g·plant−1), essential oil content (0.695%, DW), and essential oil yield (10.01 kg·ha−1) were achieved under F4 (R:B = 78:22). These parameters gradually declined with decreasing red light proportions. Gas chromatography revealed that the flower essential oil—derived from three pooled samples of each lighting treatment—was dominated by 2,2,6-trimethyl-3-keto-6-vinyl tetrahydropyran, with the highest relative abundance under F3 (R:B = 55:45; 39.9%) and the lowest under F2 (32.5%). The strongest anti-inflammatory activity was detected under F3, but no clear trend was evident regarding antimicrobial activity. These findings provide a foundation for further in-depth research aimed at optimizing supplemental LED spectra to maximize flower productivity, essential oil quality, and value of C. indicum in cultivation systems.