Beyond the PAR spectra: impact of light quality on the germination, flowering, and metabolite content of Stevia rebaudiana (Bertoni)

Abstract

BACKGROUND: Stevia rebaudiana is a high value crop due to the strong commercial demand for its metabolites (steviol glycosides) but has limited geographical cultivation range. In non-native environments with different daylength and light quality, Stevia has low germination rates and early flowering resulting in lower biomass and poor yield of the desired metabolites. In this study, artificial lighting with light-emitting diodes (LEDs) was used to determine if different light quality within and outside of the photosynthetically active radiation (PAR) range can be used to improve germination rates and yields for production of steviol glycosides for the herbal supplement and food industry.RESULTS: Plants treated with red and blue light at an intensity of 130 ∼mol m −2 s −1 supplemented with 5% of UV-A light under a 16-h photoperiod produced the most desirable overall results with a high rate of germination, low percentage of early flowering, and high yields of dry leaf, stevioside and rebaudioside A, 175 days after planting. CONCLUSION: While red and blue light combinations are effective for plant growth, the use of supplemental non-PAR irradiation of UV-A wavelength significantly and desirably delayed flowering, enhanced germination, biomass, rebaudioside A and stevioside yields, while supplemental green light improved yield of biomass and rebaudioside A, but not stevioside. Overall, the combination of red, blue and UV-A light resulted in the best overall productivity for Stevia rebaudiana.

Artificial Lighting Photoperiod Manipulation Approach to Improve Productivity and Energy Use Efficacies of Plant Factory Cultivated Stevia rebaudiana

“…Therefore, the full spectral composition available in natural daylight may not be the most optimized spectra for the plant, and as such, the DLI based on natural light alone is not a proper reference towards maximizing plant productivity, as it does not consider the qualitative aspect of the light. This is apparent from studies showing that artificial lighting with different spectral composition but with identical PPFDs and DLI, having significantly different yields [25,39].…”

“…Past studies on the productivity of Stevia under artificial lighting did not consider the effects of DLI [22][23][24]. Studies typically focused on the effects of light intensity or photoperiod without considering the total DLI, while studies with constant DLI employed varying spectral compositions [2,22,25,26]. When experiments are conducted using light sources with similar intensity but different photoperiods, the overall DLI can vary significantly, as reported in experiments comparing a 12-h photoperiod with a 16-h photoperiod under identical intensities, where the difference in DLI varied by as much as 33% [22,27].…”

Effect of UV Stress on the Antioxidant Capacity, Photosynthetic Activity, Flavonoid and Steviol Glycoside Accumulation of Stevia rebaudiana Bertoni

“…At the same time, the blue spectrum promotes the maximum accumulation of phenolic compounds [32] and causes an increase in the SG content in stevia leaves during callus culture propagation [33]. Green light was found to improve biomass yield and rebaudioside A content, but not SG [35].…”

“…Lengthening the dark period promotes flowering and a reduction in vegetative growth, and when artificial supplementary lighting extends the daylight hours, the plant does not bloom [30]. The morphogenetic responses of S. rebaudiana to light manipulation in in vitro culture are limited [26,[31][32][33][34][35][36][37][38].…”

“…It is known that UV irradiation affects the photosynthetic apparatus and the synthesis of primary and secondary metabolites of different plants [39][40][41]. UV-A prevents early flowering and increases biomass and Rb A and SG content in stevia plants [35]. However, there is extremely little information about the effect of different ranges of UV irradiation on the concentration and synthesis of Rb A and SG.…”