Quercetin and Steviol Glycosides Accumulation in Stevia Rebaudiana Plants as Affected by Supplementary to the Main Photosynthetic Photon Flux Uv-C Irradiation

The aim of the study is to investigate the effect of UV-C irradiation of plants, supplemented with the main PAR radiation, on the synthesis and accumulation of steviol glycosides and quercetin in the leaves of stevia cuttings during vegetative propagation, as well as in adult plants. The hypothesis of a possible increase in the synthesis of secondary metabolites was tested using quercetin and steviol glycosides in the leaves of growing cuttings and adult stevia plants as an example under three variants of LED lighting with supplementation of the main photosynthetic photon flux with UV-C radiation (wavelength 275 nm, power 50–60 mW/m2). The content of quercetin and steviol glycosides was determined by high-performance liquid chromatography. The addition of UV-C spectrum negatively affected the growth and development of shoots from cuttings; a decrease in plant height and weight, as well as leaf area, was observed compared to the control. The amount of steviol glycosides in adult plants in the variant close to daylight (C14Z40K42DK4) was the lowest (2.23 %), while in the variant with UV-C it increased almost twofold (4 %). In the variant C20Z20K53DK7 with UV-C, it was 15 % higher and reached the maximum (5 %). Under red-blue spectrum diodes with a large proportion of far-red (C23Z4K54DK19), it was the same as in the variant without the addition of UV-C (about 4 %). Data were obtained on the positive effect of UV-C radiation, supplementing the main PAR flux, on the accumulation of quercetin in actively developing stevia leaves and an increase in the total content of steviol glycosides during irradiation of adult plants and cuttings.