GROWTH AND PHYTOCHEMICALS IN LETTUCE AS AFFECTED BY DIFFERENT RATIOS OF BLUE TO RED LED RADIATION

Light-emitting diodes (LED) lamps have been widely used to promote the growth and quality of horticultural crops. Five ratio levels of red 100% (red only), red 90% + blue 10%, red 80% + blue 20%, red 70% + blue 30% and blue 100% (blue only) radiation in a closed plant production system (CPPS) were provided to analyze the effect of combination of red and blue LED on growth and phytochemicals in lettuce (Lactuca sativa L. ‘Jeokchima’). Photoperiod, air temperature, photosynthetic photon flux, relative humidity, and CO₂ concentration in CPPS were maintained at 16/8 h, 22/18°C, 230 μmol m^-2 s^-1, 70%, and 800 μmol mol^-1, respectively. Nutrient solution with temperature 22°C, electric conductivity 1.5-1.8 mS cm^-1, and pH 5.5-6.0 was circulated from a nutrient solution tank to growing beds. Growth and phytochemicals in lettuce was significantly affected by the different ratios of blue to red LED illumination. Lettuce grown under red light showed the greatest number of leaves, leaf area, leaf fresh weight and dry weight. Maximum ascorbic acid in lettuce was found under RB91 treatment (red 90% + blue 10%). Anthocyanins increased with the increasing addition of blue light.