GROWTH AND ACCUMULATION OF PHENOLIC COMPOUNDS IN THYME (Thymus vulgaris) BASED ON THE BALANCE OF RED AND BLUE LED LIGHTS

The new plant production methods that use artificial light to replace or complement sunlight have proven that changes in the wavelength of incidental light result in variations in growth, development and secondary metabolism of plants, depending on the genotype and other environmental conditions. However, these methods have been scarcely studied in medicinal and edible plants. The aim of this study was to determine the response of thyme plants (Thymus vulgaris) under different wavelengths. The plants were exposed to red light (660 nm), blue light (440 nm), white light and two proportions of red-blue for 16 hours a day at an intensity of 25 µmol m−2 s−1. The treatments were isolated from sunlight and from each other. Red light was found to promote the formation of etiolated plants, with a low accumulation of chlorophyll, dry matter and phenolic compounds compared to the white light treatment. Blue light generated compact plants with a higher accumulation of chlorophyll and dry matter than red light, but similar to the white light treatment. In terms of phenolic compounds, accumulation was higher under the two latter treatments. The planting of thyme under a combination of blue-red light at a 3:1 ratio was found to result in a compact growth and to improve the accumulation of phenolic compounds.