The effect of short-term red lighting on Brassicaceae microgreens grown indoors

We evaluated the effect of 638 and 665 nm red lighting on growth and nutritional quality parameters of Brassicaceae microgreens. Experiments were performed in closed-environment chambers (16 h photoperiod; 21/17 degrees C). Mustard (Brassica juncea L., 'Red Lion'), red pak choi (Brassica rapa var. chinensis, 'Rubi F-1') and tatsoi (Brassica rapa var. rosularis) were grown in peat substrate for 10 days. Solid-state lighting units, consisting of red 638 nm, 665 nm, blue 455 nm and far red 731 nm LEDs at total photosynthetic photon flux density (PPFD) of 200 mu mol m(-2) s(-1) were used for microgreen illumination from sowing. Three days before harvest the total PPFD level was raised to 300 mu mol m(-2) s(-1). In the control treatment, all four spectral components were raised proportionally. The red light treatment was illuminated with only 638 or 665 nm light at 300 mu mol m(-2) s(-1). At harvest, growth parameters and phytochemical contents were determined. 638 and 665 nm light, applied before harvest, caused stem elongation, increased fresh weight and decreased leaf area, but this varied between species. Red light improved the nutritional quality of microgreens. Comparison of different red-wavelength effects showed that more antioxidants, especially ascorbic acid and beta-carotene, were accumulated in microgreens exposed to 638 nm, than exposed to 665 nm light.