Warm and Cool Full Spectrum LED Supplements Impact Key Flavor Volatiles in Hydroponically Grown Basil
Hammock, H. A., D. A. Kopsell, and C. E. Sams.  2018.  HortScience, 53(9):S55. This Poster won Second Place at the ASHS Annual Conference Graduate Student Poster Competition.

Abstract:
Blue (B) and red (R) wavelengths within the photosynthetically active radiation (PAR) spectrum drive primary metabolism in plants. Spectral quality is an important factor in greenhouse production and directly impacts plant growth and development. Light emitting diodes (LEDs) offer excellent spectral control and allow growers to optimize biomass yield and plant quality throughout growing seasons. Full spectrum white LED lights are becoming popular for commercial production of high value specialty crops, but research is needed to determine the impact of warm and cool full spectrum supplemental lighting in comparison to narrowband B/R LEDs on secondary metabolism and flavor volatile production. The objective of this study was to establish impacts of full spectrum LEDs and narrowband B/R LEDs on key flavor volatiles in hydroponic basil (Ocimum basilicum var. ‘Italian Large Leaf’). A total of four treatments were used: warm white LEDs (3200 K), cool white LEDs (5600 K), 20B (447 nm)/80R (627 nm) narrow band LEDs, and one non-supplemented natural light control. Each supplemental lighting treatment provided 150 µmols.m-2.sec-1 for 24 h. The daily light integral (DLI) of the natural light control averaged 9.8 mol.m-2.d-1 during the growth period (ranging from 4 to 20 mol.m-2.d-1). Relative humidity averaged 55%, with day/night temperatures averaging 29.8 °C/23.6 °C, respectively. Basil plants were grown in a closed gutter hydroponic system with standard fertility regimen and harvested 45 d after seeding. Flavor volatile compounds were quantified using GC-MS. Concentrations of key flavor volatiles varied significantly across lighting treatments. Eucalyptol, linalool, limonene, â-myrcene, and á/â-pinene showed increased concentrations under the 3200 K LED treatment in comparison to the 5600 K LED treatment. With the exception of methyl eugenol, all compounds evaluated were significantly higher in LED treatments as compared to the natural light control. Concentrations of some undesirable flavor compounds, such as dimethyl sulfide and benzaldehyde, followed a similar trend as many of the evaluated compounds, with increased concentrations found in the 3200 K LED treatment in comparison to the 5600 K treatment and natural light control. In general, plants under the full spectrum treatments showed increased VOC concentrations than plants under the 20B/80R treatment, suggesting that fluence and spectral quality influence secondary metabolism. The results of this study show that full spectrum LEDs can manipulate secondary metabolism and flavor volatile production in basil, making the selection of LED spectral quality critical to maximize quality.