Volatile oil concentration and growth of thyme (Thymus vulgaris L.) plants responded to red to blue light ratios

The objective of this study was to evaluate the growth and volatile oil concentrations of thyme (Thymus vulgaris L.) plants under different red to blue light ratios of 4:1 (R4B1), 2:1 (R2B1), 1:1 (R1B1), and 1:2 (R1B2) with light-emitting diodes (LEDs) and fluorescent light (FL) in a plant factory. Thyme plants were sampled at 3 intervals of 12, 24, and 36 days after treatment. The results showed that the growth and medicinal components accumulation of thyme plants were significantly affected by different light qualities. The significant higher biomass, leaf area, and volatile oil concentrations of thyme plants were obtained under treatment R4B1 compared with treatment FL, regardless of the cultivation period. When analyzing the volatile oil constituents of thyme plants, thymol, γ-terpinene, p-cymene and α-terpinene were detected as the main constituents. However, the response of these different constituents varied with different light qualities. The above results indicated that the targeted constituent concentrations could be manipulated by employing different light qualities according to various purposes. Based on the above results, R4B1 can be considered as the optimal light treatment for thyme plants growth and volatile oil production in a closed production system with LEDs.