Light spectral quality on production of lettuce, cucumber and sweet pepper seedlings

Abstract

The response of lettuce (Lactuca sativa), cucumber (Cucumis sativus) and sweet pepper (Capsicum annuum) seedlings to light spectral quality when grown under continuous illumination was investigated in relation to the growth, dry matter, and seedling quality index. Different light quality treatments were applied during the germination and plant growth steps, using cool-white fluorescent bulbs (CWF) or red and blue light-emitting diodes (LEDs) at an fluence of 30 and 25 μmol m^-2 s^-1 photosynthetic photon flux density (PPFD), respectively. Treatments were arranged in a completely randomized design in a 3×2 factorial: three vegetable species (lettuce, cucumber and sweet pepper) and two light quality treatments (white fluorescent light or red and blue LEDs), with four replications. Results showed that the vegetables had distinct growth responses to different light-quality treatments. Number of leaves was significantly greater under blue and red LEDs light compared to the CWF lighting, for the three vegetable species. Shoot length and root collar diameter of lettuce and sweet pepper were significantly greater under blue and red LEDs light compared to the CWF light, while cucumber seedlings showed no significant differences. Root length, root dry matter and Dickson quality index (DQI) of the cucumber seedlings was significantly greater under blue and red LEDs light compared to the CWF light, while lettuce and sweet pepper seedlings showed no significant differences. Shoot dry matter (SDM) and total dry matter (TDM) of the lettuce and cucumber seedlings were greater when grown under blue and red LEDs light. The lighting with blue and red wavelengths from LEDs resulted in better quality cucumber seedlings compared to the cool-white fluorescent light. The shoot growth rate of lettuce seedlings was favored by blue and red LEDs light. Different spectral qualities have little effect on growth and development of sweet pepper seedlings.