2017 ASHS Annual Conference

This study was conducted to evaluate the effect of the irradiation period and ratio of far-red (FR) LED light combined with red (R) and blue (B) LED lights on the growth and phenolic content of Crepidiastrum denticulatum, a valuable medicinal plant. Three-week-old C. denticulatum seedlings were transplanted to a hydroponic system in a plant factory. After the ratio of R to B LEDs was set at 8:2 (R8B2), the ratio of R to FR LEDs was adjusted to 0.7, 1.2, 4.1, and 8.6. R8B2 and commercially available LEDs were used as control I and II, respectively. The plants were cultivated under the light treatments and some plants of control I were subjected to four different R/FR ratios for 30 min before the end of the light period (EOL). Growth and phenolic compounds related parameters were measured 6 weeks after treatment. Shoot fresh and dry weight, leaf area, leaf length, and leaf width under R/FR ratios of 0.7 and 1.2 were 1.8- to 2.4-times higher than those of the control plants. Continuous R/FR 0.7 and 1.2 irradiation reduced the total phenolic content per dry weight compared with the control, although it was not significant. The total phenolic content per shoot increased more than 2-fold under R/FR 0.7 and 1.2 compared with that of control I. The content of individual phenolic compounds followed the same tendency as the total phenolic content. Chlorogenic acid, caffeic acid, and chicoric acid content per shoot under R/FR 0.7 and 1.2 increased 1.3- to 1.8-times compared with control I. FR EOL treatments did not show any significant effect on growth and bioactive compounds. The positive effects of FR LEDs on growth and phytochemical content were also proved in our previous study using lettuce. These results suggest that supplemental irradiation with FR LEDs should be considered to improve both C. denticulatum yield and quality in terms of phytochemicals, when grown in a plant factory with artificial lighting.