Effect of LED light quality on the growth and photomorphogenesis of basil in closed-type plant factory

This study was conducted to investigate effects of LED light quality on the growth and photomorphogenesis of basil (cv. ‘Amethyst Improved’) in a closed-type plant factory. Basil was sown on a urethane sponge and grown for two weeks under a White-LED. When the first main leaf appeared, the plants were transplanted into a nutrient solution hydroponic system (24 ± 2 °C, RH 55±10%) and using a standard nutrient solution for leafy vegetables (N 17.3, P 4.0, K 8.0, Ca 8.0, Mg 4.0, S 4.0 me·L-1). To compare growth and internal traits of basil under various light qualities, QD-LED (combining blue, red, and far-red light), Blue+Red-LED (blue and red wavelengths at a ratio of 1:3), White-LED, 100% Blue-LED, and 100% Red-LED were used to cultivate basil for 35 days. Photosynthetic photon flux density (PPFD) was 200 ± 10 μmol·m-2·s-1 and the light was provided for 16/8 hours (Light/Dark). The plant height was significantly the longest at 26.1 cm in QD-LED, and the number of leaves was the highest at 16.00 ea in QD-LED, but not significant. The leaf length was the longest at 10.9 cm in QD-LED and the shortest at 8.10 cm in White-LED. The leaf width was up to 26% wider in Blue+Red-LED, but there was no statistical significance. The leaf thickness was the thickest at 0.33 mm for Blue+Red-LED and Red-LED, which have a high proportion of red light, and the thinnest at 0.26 mm for Blue-LED. In the case of the curvature index (CI), which indicates the morphological characteristics of basil leaves, the values were highest for Blue+Red-LED and Red-LED. The internode length and leaf stalk length were significantly the longest at 5.73 cm and 3.04 cm, respectively, for QD-LED, and the stem diameter at 5.26 mm for QD-LED. The shoot fresh weight was 26.0 g in QD-LED, which was significantly higher than the other treatment groups by up to four times, but the root fresh weight was the highest at 5.99 g in Blue+Red-LED. On the other hand, the shoot and root dry matter ratio were the highest at about 9% and 5%, respectively, in White-LED. The maximum quantum yield (FvFm) did not differ significantly between the treatment groups, but the value was significantly lowest at 0.79 for Red-LED. The chlorophyll content (SPAD), normalized difference vegetation index (NDVI), and anthocyanin reflectance index (ARI1) values were up to 27% higher in Blue+Red-LED than in other treatment. Also, the DPPH radical scavenging activity and total phenol content were the highest in Red-LED at 74% and 9.47 mgGAE·g-1FW, respectively. As a result, basil (cv. ‘Amethyst Improved’) grew best in QD-LED, and its antioxidant effect was the best in Red-LED. In addition, it was confirmed that the curvature and morphological characteristics of basil leaves changed depending on the ratio of red light at 600-700 nm.