2017 ASHS Annual Conference

The use of light-emitting diodes (LEDs) in commercial greenhouse production is rapidly increasing due to technological advancements, increased spectral control, and improved energy efficiency. Research is needed to determine the value and efficacy of LEDs in comparison to traditional lighting systems. The objective of this study was to establish the impact of blue(B)/red(R) LED lighting ratios on flavor volatiles in hydroponic basil (Ocimum basilicum var. ‘Genovese’) in comparison to non-supplemented natural light controls and traditional high pressure sodium (HPS) lighting. ‘Genovese’ basil was chosen because of its high market value and demand among professional chefs. Emphasis was placed on investigating concentrations of important flavor volatiles in response to specific ratios of narrow-band blue/red (447nm/627nm) LED light. A total of nine lighting treatments were used: Two non-supplemented natural light controls, one HPS treatment, and six LED treatments with progressive B/R ratios as: 10B/90R; 20B/80R; 30B/70R; 40B/60R; 50B/50R; and 60B/40R. Each supplemental lighting treatment provided 8.64 mol m^-2 d^-1 (100 µmols m^-2 sec^-1, 24 hours per day). The daily light integral (DLI) of the natural light controls averaged 9.5 mol m^-2 d^-1 during the growth period (ranging from 4 to 18 mol m^-2 d^-1). Relative humidity averaged 65%, with day temperatures averaging 29.4°C and night temperatures averaging 23.8°C. Basil plants were harvested 45 days after seeding, and flavor volatile profiles were obtained by GC-MS (Agilent 6890N). Flavor volatile concentrations varied significantly among lighting treatments. Many compounds showed a non-linear relationship with increasing B/R LED ratios, with the greatest bioaccumulation observed in LED ratios ranging from 20B/80R to 50B/50R. However, the concentrations of some compounds, such as d-limonene and methyl eugenol, were 3-4x higher in the control treatments, and decreased significantly for basil grown under supplemental lighting treatments. The concentrations of eugenol and methyl eugenol were inversely correlated with the B/R ratio of LED treatments, and the ratio of eugenol to methyl eugenol varied drastically among LED treatments and controls. The concentration of alpha-cubebene increased 50x in basil grown under the 20B/80R treatment, as compared to the non-supplemented controls. Eucalyptol, camphor, camphene, and (+)-3-carene concentrations were also increased 3-4x under the 20B/80R treatment, as compared to the controls and HPS treatment. Maximum concentrations for each compound varied among lighting treatments, but most were highest under 20B/80R to 50B/50R. The application of LED lighting systems to supplement natural DLI may be beneficial for improving overall flavor quality of basil and other high-value specialty herbs.