Effect of far-red and UV-B light on the growth and ginsenoside content of ginseng (Panax ginseng C. A. Meyer) sprouts aeroponically grown in plant factories

Ginseng (Panax ginseng C. A. Meyer) sprouts have a high content of saponins (ginsenosides) in their shoots, and their value as medicinal vegetables is increasing. However, there are no standardized cultivation guidelines for ginseng sprouts for raw foods, and the effect of light quality on growth and ginsenoside content in ginseng sprouts is not clear. The objective of this study was to analyze the growth and ginsenoside content of ginseng sprouts aeroponically grown in plant factories under supplemental far-red and ultraviolet-B (UV-B) light treatments. One-year-old ginseng seedlings were transplanted into a plant factory with a photosynthetic photon flux density (PPFD) of 50 µmol m⁻² s⁻ ¹using light-emitting diodes of red:blue = 1:1. Based on the phytochrome photostationary state value of solar radiation equal to 0.72, far-red light treatment with 18 µmol m⁻² s⁻¹ for 16 h per day was applied from 0, 6, and 12 days after transplanting (DAT). For UV-B light treatments, different UV-B radiation exposure times with 0.1 W m⁻² dose were applied for 1, 2, and 3 h on the day before harvest. Under the control condition, stem hardness steeply increased after 18 DAT, making raw consumption of whole ginseng sprouts difficult. When the far-red light was applied, the electron transport rates of photosystems II and I of ginseng leaves increased and nonphotochemical quenching decreased at a high PPFD range, but no differences were found at 50 µmol m⁻² s⁻¹. Far-red light treatments significantly lowered the stem hardness but did not induce significant differences in other growth factors or ginsenoside contents regardless of duration. Under additional UV-B radiation, no significant differences in photochemical characteristics or ginsenoside content were observed. As a result, additional far-red lighting can be utilized to maintain low stem hardness and extend the cultivation period.