2017 ASHS Annual Conference

Light-emitting diodes (LED) are an emerging lighting technology for controlled environments. Recent research is establishing added benefits to plant quality under narrow-band blue and red LEDs. The objective of this study was to compare impacts of different wavelengths of blue light on biomass parameters and nonstructural water soluble carbohydrates in kale (Brassica oleracea var acephala) microgreens. A comparison to white LEDs was also made. ‘Toscano’ kale were seeded into shallow (25.4 cm x 50.8 cm) flats at 10 g per flat. Flats were placed into controlled environment chambers (Model E15; Conviron, Pembina, ND) at a constant air temperature of 22 °C and germinated in the dark for 24 h. Upon germination, experimental sole source LED light treatments were applied as: 1) white (Orbital Technologies, Madison, WI); 2) 400 nm; 3) 420 nm; 4) 450 nm; and 5) 470 nm (Ray22; Fluence Bioengineering, Austin, TX), with a 14-h photoperiod and a light intensity of 250 µmol·m^-2·s^-1 for all treatments. All blue light treatments contained 625 nm and 660 nm wavelengths at a ratio of 40% blue/60% red light. Three flats were used per light treatment and the experiment was repeated two times. All microgreens were harvested 16 d after seeding and measured for biomass, % neutral detergent fiber (%NDF), and concentrations of nonstructural water soluble carbohydrates. Kale microgreen shoot fresh mass (FM; P≤0.001), dry mass (DM; P≤0.001), %DM (P≤0.001), and %NDF (P≤0.001) varied in response to blue light treatments. The white LED treatment averaged 106.3 g FM per flat, while the 470 nm treatment averaged 54.9 g FM per flat. The highest DM per flat was under the 400 nm treatment (14.8 g DM), while the lowest DM per flat was under the 470 nm treatment (7.2 g DM). The 400 nm treatment had the highest %DM (18.8%), but the lowest %NDF (9.6%). Kale water soluble sucrose (P≤0.001) was influenced by light treatment; however, glucose and fructose were not. Concentration of sucrose (47.5 mg·g^-1 DM) for the 420 nm treatment were significantly higher than the white light treatment (18.5 mg·g^-1 DM). Even though the lower blue LED wavelengths produced less FM, these two treatments resulted in significantly higher microgreen %DM, lower %NDF, and higher soluble sucrose. Data shows that increases in %DM under the 400 and 420 nm wavelengths were most likely due to increases in carbohydrate production, which may positively impact consumer preference.