2018 ASHS Annual Conference

Sweet basil (Ocimum basilicum) is widely used as a culinary herb and medicinal plant due to its unique aromatic flavor and relatively high content of phenolic compound. Effects of supplemental UV-B radiation and photosynthetic photon flux density (PPFD) on the growth and nutritional quality of green basil ‘Improved Genovese Compact’ and purple basil ‘Red Rubin’ were evaluated. The experiment was setup in a 2×5 full factorial split-plot design with light intensity as the main plot and UV-B radiation as subplot. Uniform basil seedlings with one pair of fully-expanded true leaves were transplanted and moved into a walk-in growth room for two PPFD treatments, 160 and 224 mmol·m^-2·s^-1. Five or two days before harvest, basil plants were applied with one of the five supplemental UV-B radiation levels (no UV-B radiation, control; UV-B radiation of 1 h per day for 2 days, 1H2D; 1 h per day for 5 days, 1H5D; 2 h per day for 2 days, 2H2D; and 2 h per day for 5 days, 2H5D). All plants were sub-irrigated as needed using a nutrient solution with electrical conductivity of 2.0 dS·m^-1 and pH of 6.0, and the room temperature was maintained at 23.9/21.2ºC day/night. The results showed that 2H5D treatment significantly decreased the net photosynthetic rate, transpiration rate, stomatal conductance, and Fv/Fm of green/purple basil plants by 68%/70%, 55%/68%, 65%/76%, and 9%/12%, respectively, and PPFD had no effects. Plant height, total leaf area, and shoot FW and DW of green and purple basil plants were decreased by supplemental UV-B and lower PPFD treatments, and no interactive effects were observed. The shoot dry matter percent of green and purple basil plants were increased by 14% and 19%, respectively, under 2H5D UV-B treatment compared with control. The anthocyanin, total phenolics, and flavonoid concentration of green basil plants under supplemental UV-B treatments were enhanced by 18%-22%, 35%-126%, and 80%-169%, respectively, whereas anthocyanin concentration of purple basil plants showed no difference, and phenolic and flavonoid concentration of purple basil were slightly decreased under 1H2D treatment. Considering the yield reduction and nutritional content enhancement of basil plants by supplemental UV-B radiation, 1H2D/1H5D UV-B treatments with PPFD of 224 mmol·m^-2·s^-1 was recommended for green basil production under controlled environment, and supplemental UV-B radiation was not recommended for purple basil production.