2019 ASHS Annual Conference

Effects of light quality on the growth and nutritional quality were evaluated on six herbs and leafy greens, including basil (Ocimum basilicum) ‘Improved Genovese Compact’ (green) and ‘Red Rubin’ (purple), green kale ‘Siberian’ (Brassica napus pabularia), red kale ‘Scarlet’ (B. oleracea), green mustard ‘Amara’ (B. carinata), and red mustard ‘Red Giant’ (B. juncea). Five light quality treatments, including two full spectrum light treatments (white fluorescent lamp, WFL; and white light-emitting diode lamp, WLED) and three combinations of red and blue LED light treatments with different red: blue (R:B) ratios (R:B=1.18, R1B1; R:B=3.44, R3B1; R:B=7.84, R8B1) were applied to plants with the same photosynthetic photon flux density at 224 umol·m^-2·s^-1 with a 16-h photoperiod. All experiments were conducted in a walk-in growth room. 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 23.1/20.5ºC day/night. Results indicated that although plant responses to light quality was species dependent, in general, blue light improved plant photosynthesis and nutritional quality while red light stimulated stem elongation and leaf expansion, resulting in increased crop yield. The net photosynthetic rate of purple basil and red kale plants were both the highest under R1B1 treatment, while no difference was observed on the other plant species, but tended to increase with increasing blue light percentage in green basil and green kale plants. On the contrary, the plant height and leaf area of basil and kale plants were the highest under R8B1 treatment, which has the highest red light percentage. Consistent with the morphological data, the shoot fresh weight of basil, kale, and mustard plants was the highest under R8B1 treatment, which was increased by 24%-25%, 22%-32%, and 5%-23%, respectively, compared to R1B1 treatment. The nutritional quality of basil plants, including the concentrations of phenolics and flavonoids and the antioxidant capacity of plant leaves, was improved by the combined red and blue LED treatments compared to full spectrum light treatments, and the accumulation of phenolics and flavonoids tended to increase with increasing blue light percentage. In kale plants, the nutritional quality was promoted by WFL and RIB1 treatments, which was also observed in mustard plants. Considering the yield and nutritional quality, combined red and blue LEDs with red light percentage around 75% was recommended for herbs and leafy green production under indoor controlled environment.