Storage of grafted-tomato seedling under low-light conditions with light-emitting diodes and an electroluminescent sheet

Abstract

We investigated the effects of photosynthetic active radiation generated by blue (465 nm peak wavelength) light-emitting diodes (LEDs), red (625 nm peak wavelength) LEDs, or an electroluminescent sheet (EL) (two peak wavelengths: 454 and 565 nm), and dark conditions on the quality preservation of tomato (Solanum lycopersicum) seedlings during low-light irradiation (LLI) storage. The photosynthetic photon flux density (PPFD) at the plant canopy level was automatically controlled using a proportional-integral-derivative (PID) controller to maintain the CO2 exchange rate of the seedlings at zero. Nine seedlings were stored for 21 d in a storage case at 10 ± 0.5°C and at greater than 95% RH. The total dry weight of the tomato seedlings after storage under any LLI was significantly greater compared to that before storage and during dark storage. The PPFD required for maintaining the CO2 exchange rate of the seedlings at zero under all LLI treatments over a 21 d storage period gradually decreased due to the low-light adaptation of the plant. The mean PPFDs to maintain a light compensation point under the blue LED-, red LED-, and EL-LLI for the last week of storage were 5.15, 5.03, and 5.20 µmol·m−2·s−1, respectively. The spectral distribution of the EL light may help preserve seedling quality better than that of the blue or red LED lights and the dark condition, providing a vigorous seedlings with upright morphology and significantly lower specific leaf area (cm2·g−1 DW), which reflects a thick leaf. For green plant storage, an EL or other kind of mixed light is able to control PPFD automatically, which may help maintain seedling quality for more than 3 weeks longer than with blue or red monochromatic light.