Manipulating light quality to promote shoot growth and bioactive compound biosynthesis of Crepidiastrum denticulatum (Houtt.) Pak & Kawano cultivated in plant factories

Crepidiastrum denticulatum (Korean common name: i-go-deul-ppae-gi) is a valuable medicinal plant used in the pharmaceutical industry and as a raw material of functional foods. In this study, we investigated the effect of light quality on C. denticulatum growth, with the goal of improving the species’ biomass and bioactive compound content when grown in plant factories with artificial lighting. Three-week-old seedlings were grown for 6 weeks in a plant factory under fluorescent lamps (control) and various sets of light-emitting diodes (LEDs): three monochromatic [red (R), green (G), and blue (B)], several dichromatic RB with different ratios of R and B [R:B = 6:4 (R6B4), 7:3 (R7B3), 8:2 (R8B2), and 9:1 (R9B1)], and several trichromatic RGB [R:G:B = 5:1:4 (R5G1B4), 6:1:3 (R6G1B3), 7:1:2 (R7G1B2), 8:1:1 (R8G1B1), and 9:1:0 (R9G1B0)]. Shoot biomass (fresh weight), leaf area, leaf shape index, and water content of the shoot were significantly higher in the RGB group than in the monochromatic and RB groups. Increasing the percentage of R light improved shoot growth in the presence of G light, as in the RGB group, and this was accompanied by a high photosynthetic rate, light absorbance rate, and electron transport rate. The contents of total phenolics and hydroxycinnamic acids per unit dry weight did not differ between plants subjected to the different light quality treatments, and the contents per shoot were thus positively associated with shoot biomass. Overall, R8G1B1 was the most effective treatment for increasing shoot biomass and the accumulation of bioactive compounds; the shoot fresh weight and total hydroxycinnamic content of R8G1B1 were significantly higher, by 50 % and 60 %, respectively, than those of the control. Thus, light quality affects the biosynthesis of bioactive compounds and the shoot biomass of C. denticulatum.