Daily Light Integral Supplements Alter Key Flavor Volatiles in Hydroponically Grown Basil
Hammock, H. A., D. A. Kopsell, and C. E. Sams.  2018.  HortScience, 53(9):S55.

Light quantity, quality, and duration are three primary factors that impact plant growth and development. Light emitting diodes (LEDs) offer control for each of these parameters and allow commercial growers to optimize biomass yield and plant quality throughout growing seasons. While many studies show LED supplementation is useful for high-value specialty crop production, research is needed to determine the value and efficacy of LED lighting systems in comparison to traditional lighting systems. Research determining the impact of daily light integral (DLI) and spectral distribution on secondary metabolism and flavor volatile production could be of value to producers. The objective of this study was to establish the effects of progressive DLIs using LED and high-pressure sodium (HPS) supplementation on key flavor volatiles in hydroponic basil (Ocimum basilicum var. ‘Genovese’) across different growing seasons. A total of nine lighting treatments were used: one non-supplemented natural light control, two HPS treatments with DLIs as 6 h and 12 h, and six 20B/80R LED treatments with progressive DLIs as 3 h, 6 h, 9 h, 12 h, 18 h, and 24 h. Each supplemental lighting treatment provided 100 µmols.m-2.sec-1. The DLI of the natural light control averaged 9.9 mol.m-2.d-1 during the growth period (ranging from 4 to 20 mol.m-2.d-1). Relative humidity averaged 50%, with day/night temperatures averaging 29.4 °C/23.8 °C, respectively. Basil plants were harvested 45 d after seeding, and flavor volatile profiles were measured using GC-MS. Flavor volatile concentrations varied significantly among seasons and lighting treatments. Many compounds showed a non-linear relationship as DLIs increased, with the greatest flavor volatile concentrations observed in LED ratios ranging from 12-24 h and the 6 h HPS treatment. The 6 h HPS lighting treatment produced comparable volatile organic compound (VOC) concentrations to the 24 h LED treatment, suggesting that DLI is only one of the many factors that drives secondary metabolism resource allocation. Further, concentrations of some compounds, such as methyl eugenol, were 3-4x higher in the 3 h LED treatment and decreased significantly for basil subjected to higher DLI increments. As DLI supplements were increased, secondary metabolism partitioning was significantly impacted; compared to the 3 h LED treatment, the 24 h LED treatment commonly showed significant increased mono and diterpenes, with reduced sesquiterpenes and phenols. The results of this study show that using LEDs to supplement natural photoperiods has the potential to manipulate secondary metabolism and flavor volatile production.