Manipulating growth, color, and taste attributes of fresh cut lettuce by greenhouse supplemental lighting

Abstract

Supplemental lighting (SL) is often used in greenhouse lettuce production to increase yield when the solar daily light integral is low. High-pressure sodium (HPS) fixtures are traditionally used to deliver SL, but light-emitting diodes (LEDs) have become a feasible, more energy-efficient replacement. Red light (R; 600–700 nm) and blue light (B; 400–500 nm) are especially effective in promoting photosynthesis and increasing crop growth, whereas far-red (FR; 700–800 nm) radiation has the potential to increase yield by promoting leaf expansion. We performed three greenhouse experiments with HPS or LED fixtures to determine the effects of SL on lettuce growth, coloration, and sensory attributes. We grew lettuce at 20 °C without or with SL from HPS or R + B LEDs with a 16-h photoperiod (Expts. 1 and 2). In Expt. 3, we grew plants without or with HPS SL without or with R + FR photoperiodic lighting at the end of the day during the growing (first) stage, SL from R + B or B LEDs during the finishing (second) stage, or both. SL enhanced lettuce growth and yield by 32%–104% regardless of light quality. Four hours of end-of-day R + FR lighting at 2 to 5 μmol m−2·s−1 had few effects on lettuce growth or quality attributes. Compared with lettuce with no SL, lettuce provided with R + B LED SL for 7 d before harvest was 27% darker, 76%–82% redder, and 39%–55% less yellowish. Consumers tended to prefer lettuce grown under natural daylight more than plants grown with SL, and judged it to be less bitter, to be sweeter, and to have a more likable aftertaste. We conclude that providing different types of greenhouse SL at different growing stages can improve lettuce growth and coloration but that consumers could prefer taste attributes less.