2018 ASHS Annual Conference

The young leafy greens of lettuce have higher levels of vitamins, minerals, antioxidants, and other nutrients than the older mature vegetables on a unit fresh weight basis. The usage of baby leaf and microgreen vegetables as salads and food toppings is on the rise especially in South Korea where smaller family sizes and single-person homes are increasing. Lactuca indica ‘Sunhyang’ is a cultivar developed from a wild species native to Korea that has desirable flavor, aroma, and a short growing period from seed to harvest. The purpose of this research was to determine the optimum light intensity for growing this plant cultivar as baby leaf greens and to characterize the accumulation of phytochemicals under various light levels. Seeds were sown in a standard horticultural root substrate. Upon seed germination, the seedlings were exposed to 100 μmol·m^-2·s^-1 artificial light for 14 days. When the seedling plants were 6.2 cm tall on the average with 2.9 true-leaves, they started to receive four different levels of light (50, 100, 250, 500 μmol·m^-2·s^-1) for 21 days in a controlled environment facility (plant factory). The average desirable plant height was set at 10-12 cm. Starting from 6 days after light treatment began, measurements on plant growth, hunter ‘a’ value, anthocyanins, phenolics, and chlorophyll were made 6 times at 3-day intervals. The time required for seedlings to reach the desired plant size and actual fresh weights were: 9 days and 1.1 g, 1.8 g per plant at 100 and 250 μmol·m^-2·s^-1, respectively. Under 50 μmol·m^-2·s^-1 light intensity, it took 12 days to reach the desired plant size with a fresh weight of 1.0 g per plant. When plants were grown under 500 μmol·m^-2·s^-1, it took 15 days to reach the desired plant size at 1.5 g per plant. Plants grown with 500 μmol·m^-2·s^-1 developed a reddish leaf color with a hunter ‘a’ value of -2.0-1.5. As light intensity increased, the anthocyanin and phenol contents of the leaves increased, but leaf chlorophyll content decreased. In conclusion, growing plants under 250 μmol·m^-2·s^-1 was the best for achieving the desired fresh biomass yield in a minimum time (9 days). For the highest concentrations of functional food ingredients, it is recommended to grow the plants under 500 μmol·m^-2·s^-1 light intensity for 15 days.

corresponding author: Ki-young Choi(choiky@kangwon.ac.kr)