Changes in growth characteristics and functional components of lactuca indica l. ‘sunhyang’ baby leaf vegetable by light intensity and cultivation period

Abstract

Indian lettuce (Lactuca indica L.) ‘Sunhyang’ is wild plant bred by crossing Indian lettuce and ‘Dragon’s tongue’. It has wider leaf width and less bitterness than Indian lettuce. This study was conducted to determine the optimum light intensity for growth and functional components of Lactuca indica L. ‘Sunhyang’, considered as a new wild baby leaf vegetable throughout the year. Plants were cultivated in controlled environment at temperature of 24-25°C and relative humidity (RH) of 60 ± 5% from seedling to harvest. 16 days after sowing, plants were treated with four different light intensities of PPFD (photosynthetic photon flux density) 50, 100, 250 and 500 using white LED light for 18 days. Growth characteristics, leaf color, and functional components were investigated three times (6th, 12th, and 18th day) after PPFD treatment. At light intensity of PPFD 50, 100 and 250, it took 12 days after treatment (DAT) to reach optimum size to harvest (plant height 12-14 cm). Leaf width, leaf number, and leaf area increased more in PPFD 100 and 250 than PPFD 50. At PPFD 500, it took 18 DAT to reach appropriate size to harvest. Dry weight and dry mass ratio of shoot increased with increasing light intensity, whereas specific leaf area (SLA) decreased. Chlorophyll relative value (SPAD) and leaf color differed depending on light intensity. SPAD was the lowest in PPFD 50. Hunter a* value was the highest for PPFD 250 and 500 at 12DAT. The highest relative growth rate (RGR) was observed at 0 to 6DAT for PPFD 500, 6 to 12DAT for PPFD 50 and PPFD 250, and 12 to 18DAT for PPFD 250. Parameters for root growth of Indian lettuce were affected significantly by light and DAT. Total root length was longer in PPFD 250 and 500 than that in other treatment from 6DAT. Average root diameter and volume were the largest in PPFD 500. Anthocyanin contents, total phenolic contents, and free radical activity (DPPH) were increased with increasing light level. However, levels of functional components decreased at 18 DAT. These results suggest that Lactuca indica L. ‘Sunhyang’ can grow the best when it is kept at PPFD 250 at 12 DAT for optimal growth, leaf color, and functional components.