At the last ASHS annual conference, I, Satitmunnaithum et al., (2023), presented our study on the effect of blue and white LED light ratio on red leaf lettuce, however, the effect of blue LED on red coloration during its growth is still unclear. Thus, at this year’s conference, we aim to clarify the mechanisms of red coloration under blue LED based on anthocyanin biosynthesis gene analysis and its content in vertical farming condition to stabilize its production for high market demand. To elucidate the effect of blue LED light on the red coloration of red leaf lettuce, green and red leaf lettuce (Lactuca sativa L.) were selected for this study. Both were hydroponically cultivated at the Advanced Plant Factory Research Center at Meiji University, Japan. The cultivation temperature was set at 22 ℃ with a humidity of 60%. Seeds were sown under white LED for 24 hours. Ten-day-old seedlings were transplanted to different light conditions: white LED and blue LED. The photoperiod was set for 16 hours. The nutrient solution was supplied at an EC of 1.6 mS/m^2 with a pH of 6.0 ± 0.5. Both light treatments had a PPFD of 100-120 µmol/m^2/s. After 20, 25, and 30 days of transplantation, lettuces were harvested. The red area on leaf lettuce, along with the total anthocyanin content and its precursors, as well as the expressions of anthocyanin biosynthesis-related genes such as ANS, CHS, bHLH, DFR, and HY5, were evaluated. Blue light shows a large red area on red leaf lettuce at most of the development stages resulting in a high red area percentage, while green leaf lettuce remained completely green in both light conditions. The interested genes were upregulated mostly in blue light irradiated red leaf lettuce which led to high total anthocyanin content. This can be assumed that blue LED light enhances anthocyanin synthesis in red leaf lettuce which can contribute to the stable production of red leaf lettuce in vertical farms.
