Scallion (Allium fistulosum L.) Pungency Regulated by Genetic Makeup and Environmental Conditions (Light and CO2)

To facilitate the selection of a palatable and functional food, eight green onions grown under either cool-white fluorescent lamps (CWF) or high pressure sodium lamps (HPS) were compared for their pungency, tissue nitrate and sulfate status. The effect of lighting intensity and atmospheric CO₂ levels on pungency of a selected cultivar was also investigated. Results demonstrate that there was a difference in pungency not only among cultivars, but also between tissue types and developmental stages. The pungency was inversely correlated with nitrate level in tissue, and light quality had profound impact on tissue nitrate level. Pungency in the pseudobulb and leaf of green onion responded differently to increased light intensity and elevated CO₂. The effect could be mostly explained by the relative accumulation rates of the flavor precursors and biomass. The combination of low light and high CO₂ conditions anticipated in enclosed space environments provided equivalent amount of edible biomass, and quality of food in terms of pungency as in the combination of high light and ambient CO₂. This study raised several interesting questions. For instance, should green onion be consumed immediately after harvest due to the high nitrate level, or should different horticultural practices (nutrient and light regime) be implemented to reduce the nitrate level? What effect would these strategies have on the vegetable's other quality traits? Does alternative lighting have repercussion for food quality, particularly in nitrate level?