Effect of green and UVA spectra, and pre-harvest treatments on biomass and metabolite yields of indoor cultivated stevia rebaudiana

Stevia rebaudiana is a high-value crop due to the strong commercial demand for its metabolites (steviol glycosides, SG) as an organic low-caloric sweetener with up to 300 times the sweetness of conventional sugar. Two experiments were conducted in this study. In the first experiment, treatments with varying green (GR1 & GR2), UVA (UV1 & UV2) and treatments that had both (UVGR1, UVGR2) were used. In the second experiment, separate set of plants were grown under base red-blue (RB) and natural sunlight before being transferred to GR2, UV2, UVGR2, and monochromatic light treatments of blue, green and UVA, for 3 and 10 days before harvest. RB and sunlight were used as the control for artificial and natural light respectively. Plants grown under the UVGR1 had the highest dry leaf biomass accumulation of 4.75 g plant^-1 (P < 0.05), 458% and 660% higher than the RB (0.98 g plant^-1) and natural sunlight (0.72 g plant^-1) controls. UVA had the highest metabolite (Stevioside + Rebaudioside A) concentration of 27% (P < 0.05) compared to the RB and sunlight controls at 17.24% and 15% respectively. The 10 day pre-harvest treatment with blue supplemented light yielded a dry biomass of 1.87 g plant^-1, a 190% increase compared to the RB control. However, the 3 day pre-harvest treatment had higher metabolite yields improvements compared to 10 day treatments with the highest yield obtained of 21.10% in 3-day pre-harvest irradiation that had supplemental UVA and blue light. UVGR1 was the most productive lighting strategy, resulting in the highest overall metabolite yield per plant.