2017 ASHS Annual Conference

Carotenoids are a class of secondary metabolites that contribute to photosynthetic processes and protect vital plant cell structures from photo-damage. Recent studies suggest that increasing dietary levels of specific carotenoids may help decrease the risk of certain cancers, combat the effects of aging, as well as support cardiovascular and reproductive health. In comparison to many other popular culinary herbs and spices, sweet basil (Ocimum basilicum) has high levels of nutritionally-valuable carotenoid and chlorophyll pigments. Our group has demonstrated that various blue(B)/red(R) wavelengths have significant impacts on pigment concentrations among a wide range of herbaceous specialty crops. The objective of this study was to determine the impact of B/R LED lighting ratios on pigment bioaccumulation in hydroponic basil. ‘Genovese’ pesto basil (O. basilicum var. ‘Genovese’) was specifically chosen for this experiment because of its high demand and market value. This cultivar is highly preferred by professional chefs for its intense and desirable flavor profile. In addition, the ‘Genovese’ cultivar will naturally accumulate high levels of nutritionally-important carotenoids in comparison to other popular basil cultivars. Specific narrow-band B/R wavelengths (447 nm/627 nm) were applied to investigate the impact on carotenoid and chlorophyll biosynthesis. A total of nine lighting treatments were used: Two non-supplemented natural light controls, one HPS, and six LEDs with progressive B/R ratios as: 10B/90R; 20B/80R; 30B/70R; 40B/60R; 50B/50R; and 60B/40R. Each supplemental lighting treatment provided 8.64 mol m^-2 d^-1 (100 µmols m^-2 sec^-1, 24 hours per day). The daily light integral (DLI) of the natural light controls averaged 9.5 mol m^-2 d^-1 during the growth period (ranging from 4 to 18 mol m^-2 d^-1). Relative humidity averaged 65%, with day temperatures averaging 29.4°C and night temperatures averaging 23.8°C. Basil plants were harvested 45 days after seeding and leaf tissue pigments were analyzed using HPLC (Agilent 1200 Series). The concentrations of β-carotene, chlorophyll a, chlorophyll b, antheraxanthin, violaxanthin, and neoxanthin varied significantly among B/R ratios and natural light controls. With the exception of α-carotene, violaxanthin, and neoxanthin, the 40B/60R LED lighting treatment resulted in the highest concentrations for all pigments. Further research should be conducted to establish the relationship between specific B/R wavelengths and the biosynthesis of nutritionally-important carotenoids. Because LEDs have the potential to improve antioxidant concentrations in many high-value specialty crops, various herb varieties should also be evaluated to determine the biochemical and physiological impacts of LED supplemental lighting.