2019 ASHS Annual Conference

Green light can penetrate deeper into plant canopy due to its high transmittance and reflectance than the other wavelengths, while red and blue lights are mostly absorbed by upper-level leaves. Theoretically, substituting partially red or blue light with green light could increase the light penetration to inner canopy, which could potentially increase crop yield. Therefore, we studied the effects of green light on plant photosynthesis, growth, and development in basil (Ocimum basilicum) ‘Improved Genovese Compact’ (green) and ‘Red Rubin’ (purple) plants grown under indoor controlled environment. A combined red and blue LED (R₇₅B₂₃G₁FR₁, the percentage of red, blue, green, and far-red light is 75%, 23%, 1%, and 1%, respectively) was tested as control, and three other treatments were substituting partially red light with green light (R₄₃B₂₄G₃₁FR₂), substituting partially blue light with green light (R₇₃B₁₆G₁₀FR₁), and substituting partially both red and blue light with green light (R₄₁B₁₂G₄₃FR₄). All experiments were conducted in a growth room with the same photosynthetic photon flux density at 224 umol·m^-2·s^-1 with a 16-h photoperiod. Plants were sub-irrigated as needed using a nutrient solution with electrical conductivity of 2.0 dS·m^-1 and pH of 6.0. The room temperature was maintained at 24.0/21.6ºC day/night. In green basil plants (5 internodes at harvest), the net photosynthetic rate of its upper-level leaves was the highest under R₇₅B₂₃G₁FR₁ treatment, while no difference was observed in lower-level leaves. In purple basil plants (7 internodes at harvest), the net photosynthetic rate of its upper-level leaves showed no differences among R₇₅B₂₃G₁FR₁, R₄₃B₂₄G₃₁FR₂, or R₇₃B₁₆G₁₀FR₁ treatments, while the highest under R₄₃B₂₄G₃₁FR₂ and R₇₃B₁₆G₁₀FR₁ treatments in lower-level leaves. The plant height of both cultivars was increased in R₄₃B₂₄G₃₁FR₂ and R₄₁B₁₂G₄₃FR₄ treatments. The shoot fresh weight of green basil plants was not affected by green light treatments, while increased in R₇₅B₂₃G₁FR₁ and R₇₃B₁₆G₁₀FR1 treatments in purple basil plants. The nutritional quality of green basil plants, including concentrations of anthocyanin, total phenolics and flavonoid, and antioxidant capacity of plant leaves, was increased with increasing blue light percentage (R₇₅B₂₃G₁FR₁ and R₄₃B₂₄G₃₁FR₂), while in purple basil plants, the treatment with increasing red light percentage (R₇₅B₂₃G₁FR₁ and R₇₃B₁₆G₁₀FR₁) resulted in better nutritional quality.