Impaginato 231 Adv. Hort. Sci., 2023 37(2): 231­239 DOI: 10.36253/ahsc­12062 Effect of far­red light applied at the end of the day in red and green leaf lettuce cultivars grown under two types of white LED H. Kamimaeda 1, Y. Yoshida 1, K. Tamaki 1, M. Ichihara 1, M. Akutsu 1, 2 (*) 1 Department of Electrical Engineering and Computer Science, Tokai University, 9‐1‐1 Toroku, Kumamoto‐City, Kumamoto 862‐8652, Japan. 2 Current address: Faculty of Agriculture, Shinshu University 8304, Minamiminowa‐Village, Kamiina‐County Nagano, 399‐4598 Japan. Key words: cultivar difference, end of day, far­red LED, stem elongation. Abstract: The growth and yield of 13 red and green leaf lettuce (Lactuca sativa L.) cultivars were evaluated under two types of white LED irradiation. There was a difference in growth under the two types white LEDs, specifically in the fresh total weight, fresh leaf weight and dry weight in all cultivars. In addition, the main stem elongation was confirmed for red and green lettuce cultivars under all treatments, but some cultivars promoted the growth of the main stem and the others were inhibited by treatment with far­red light applied at the end of the day (EOD­FR). Furthermore, the EOD­FR treatment affected the characteristic reactions due to white LED light quality in each of the cultivars. These results showed that it is necessary to investigate the selection of white LEDs with and without EOD­FR treatment for each lettuce cultivar. 1. Introduction Lettuce (Lactuca sativa L.), which is often cultivated not only in greenhouses but also in indoor plant factories, has become a model plant for studying the response of plants grown under LEDs (Lin et al., 2013; Yan et al., 2019). Among them, there are many reports of growth differences by irradiating red and blue LEDs with a monochromatic color, mixing red and blue LEDs, and irradiating them in combination, such as changing the irradiation time. In particular, depending on the quality of the LED light used for irradiating the plants, differences in morphological growth such as fresh and dry weight and leaf area, and in the amount of substances such as anthocyanins and vitamins in plants have been reported (Bleiss and Smith, 1985; Jieun et al., 2012; Jishi et al., 2016; Bian et al., 2018; Ishii et al., 2018). It is also known that light quality and quantity not only promotes plant photosynthesis, but also regulates plant growth (Chen et al., 2016). However, it is reported that blue lights, which affect photomorphogenesis and red, which affects photosynthesis, are (*) Corresponding author: akutsu@shinshu­u.ac.jp Citation: KAMIMAEDA H., YOSHIDA Y., TAMAKI K., ICHIHARA M., AKUTSU M., 2023 ­ Effect of far‐red light applied at the end of the day in red and green leaf lettuce cultivars grown under two types of white LED. ­ Adv. Hort. Sci., 37(2): 231­ 239. Copyright: © 2023 Kamimaeda H., Yoshida Y., Tamaki K., Ichihara M., Akutsu M. This is an open access, peer reviewed article published by Firenze University Press (http://www.fupress.net/index.php/ahs/) and distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Competing Interests: The authors declare no competing interests. Received for publication 24 July 2022 Accepted for publication 19 May 2023 AHS Advances in Horticultural Science https://doi.org/10.36253/ahsc-12062 http://www.fupress.net/index.php/ahs/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2023 37(2): 231­239 232 highly efficient for plant growth (Goto, 2005). Moreover, far­red (FR) light, along with red light, is known to have a significant effect on plant growth and has been shown to affect seed germination, plant growth, and flowering (Hisamatsu et al., 2002). It has been reported that FR LED treatment after sunset (end of day­far red: EOD­FR) promotes shoot elongation in poinsettia (Euphorbia pulcherrima) and chrysanthemum (Chrysanthemum sp.) (Lund et al., 2007; Islam et al., 2014), and also extends the hypocotyl axis in the rootstock of pumpkin (Cucurbita maxima) seedlings (Yang et al., 2012). In komatsuna (Brassica rapa var. perviridis) and pak choi (Brassica rapa var. chinensis), EOD­FR treatment has been found to increase fresh weight, dry matter weight, and leaf area (Akutsu et al., 2017). It has been reported that the fresh and dry weights and leaf length of baby leaf lettuce grown under white light irradiation with FR light increased by more than 10% compared to those grown without the FR light irradiation (Li and Kubota, 2009). In Japan, most indoor plant factories growing lettuce use red or red­ blue mixed LEDs. However, white LEDs are used extensively in our daily life and are easily available. If white LEDs can be used for lettuce production in an indoor plant factory, it may reduce the unit price spent on LEDs and consequently increase cost effectiveness. In addition, white LEDs have begun to be used for growing leafy vegetables such as leaf lettuce in plant factories, but it might be difficult to optimize the light wavelength and intensity for plant cultivation as they are originally used for indoor lighting in households. Compared to using white LED irradiation alone for plant production, it is possible to optimize the light intensity for each wavelength by combining monochromatic LED lighting (Watanabe et al., 2016), but we confirmed a difference in the growth using white LED irradiation and whether changes were made by FR LED irradiation. In this study, we investigated the effects of EOD­FR treatment on lettuce using 13 leaf lettuce cultivars under irradiation with two types of white LEDs. Plants were grown hydroponically in growth chambers to maintain environmental conditions for air temperature, humidity and concentration of CO2 other than light conditions. 2. Materials and Methods The 13 cultivars of leaf lettuce used in this study are listed in Table 1. The seeds of each cultivar were sown on urethane cubes (M Hydroponic Research Co. Ltd., Aichi, Japan) with distilled water and then ger­ minated for one week in a growth chamber (TGE­5­ 2L; Espec Corp., Osaka, Japan) at 25°C, 70% relative humidity, and 600 ppm CO2 for 16 h under continu­ ous illumination at 100 µmol/m2/s cool white fluores­ cent lamps (FHF32EX­D­HX­S; NEC Corp., Tokyo, Japan). Subsequently, the germinated seeds were transferred into a commercial A treatment nutrient solution suitable for lettuce cultivation (OAT Agrio Co., Ltd., Tokyo, Japan) and grown for an additional week. After that, eight seedlings were transferred to containers (293 mm × 211 mm × 106 mm) with 6 L of commercial A treatment nutrient solution (OAT Agrio Co., Ltd., Japan). The growth of the seedlings was observed for three weeks under the following four Table 1 ­ Lettuce cultivars used in this experiment Kinds of lettuce Cultivar name Name of seedling company Red leaf lettuce Leaf lettuce red Sakata Seed Corp., Japan Red wave Sakata Seed Corp., Japan Bancyu sun bright Nakahara Seed Co. Ltd.,Japan Sun bright Nakahara Seed Co. Ltd.,Japan Fancy red Nakahara Seed Co. Ltd.,Japan Red fire Takii Seed Co. Ltd., Japan Bancyu red fire Takii Seed Co. Ltd., Japan Sun marino Takii Seed Co. Ltd., Japan Calbee red Nakahara Seed Co. Ltd.,Japan Green leaf lettuce Summer green Sakata Seed Corp., Japan Fancy green Nakahara Seed Co. Ltd.,Japan Green wave Takii Seed Co. Ltd., Japan Yakiniku lettuce Sakata Seed Corp., Japan Kamimaeda et al. ‐ Effect of EOD‐FR light under white LEDs in lettuces 233 irradiation treatments: white LED (White A; 16 h white photoperiod, Fluorescent lamp­type LED for growing plants, Espec Corp., Osaka, Japan), FR LED irradiation for 3 h after irradiation with white A (White A + FR; 16 h white + 3 h FR photoperiod, FR LED: Valore Corp., Kyoto, Japan), another white LED (White B; 16 h white photoperiod, Fluorescent lamp­ type LED for growing plants, Espec Corp., Osaka, Japan), and FR LED irradiation for 3 h after irradiation with white B (White B + FR; 16 h white + 3 h FR photoperiod). The intensity of irradiation in white LED treatments was 100 µmol/m2/s and FR LED treat­ ment was 13.2 µmol/m2/s. The wavelengths for all LEDs are shown in figure 1. During cultivation, to their roots were given sufficient air using an air pump (Kotobuki Kougei Co., Ltd., Japan) to avoid root rot. Once a week, all solutions were replaced with fresh ones, and the electric conductivity (EC) value adjust­ ed to 1.2 dS/m1. Twenty­one days after the start of cultivation, all plants were harvested and their fresh weight, root weight, maximum leaf length, number of leaves, and SPAD value (SPAD­502; Konica Minolta Holdings Inc., Tokyo, Japan) were measured. After drying for more than three days at 70°C, the dry leaf weight and dry root weight were also measured. The plants on day 14 were alternately harvested, and all cultivation experiments were repeated twice. All data were evaluated by one­way ANOVA (analysis of vari­ ance) using the Statcel add­in (OMS Publishing Inc., Saitama, Japan) in Excel (Microsoft Corp., Redmond, WA), followed by Tukey’s multiple post­hoc compari­ son test. 3. Results Among the red leaf lettuce cultivars, the effect of white LED irradiation was observed on the fresh total weight, fresh leaf weight, root weight, and dry weight of ‘Leaf lettuce red’ (Table 2). Fresh and dry weights of ‘Red wave’, ‘Fancy red’, and ‘Calbee red’ cultivated under White A and White A + FR irradia­ tion were significantly greater than those cultivated under White B and White B + FR. The fresh total weight, fresh leaf weight, stem weight, and maximum leaf length in ‘Bancyu sun bright’ and ‘Sun bright’ grown under White A + FR and White B + FR tended to be more, and the fresh leaf weight and dry total weight in ‘Sun bright’ and the fresh total weight, fresh leaf weight, and stem weight in ‘Sun bright’ were significantly greater than those cultivated under White A and White B. The fresh total weight, fresh leaf weight, and dry total weight of ‘Red fire’ and ‘Sun marino’ cultivated under White A + FR tended to be more, and the fresh leaf weight in ‘Red fire’ and the fresh total weight in ‘Sun marino’ were signifi­ cantly greater than those cultivated under the other LEDs. All investigated items except the number of leaves and SPAD in ‘Bancyu red fire’ grown under White A and White B showed a higher value, espe­ cially for the dry total weight, which was significantly greater than that grown under White A + FR and White B + FR. Among the green leaf lettuce cultivars, in ‘Summer green’, the effect of white LED irradiation was observed on the fresh total weight, fresh leaf weight, and dry total weight (Table 3). In ‘Fancy green’, the fresh total weight, fresh leaf weight, and Fig. 1 ­ Wavelength distribution characteristics of various LED light sources used in this experiment. A= White A LED, B= White B LED, C= FR LED. (a) It was indicated relative value with the maximum peak taken as 1 against the measured light intensity. Adv. Hort. Sci., 2023 37(2): 231­239 234 maximum leaf length tended to be more when grown under White A + FR and under White B. The main stem was significantly greater than that grown under White A, but the SPAD was lower than that grown under the other LEDs. In ‘Green wave’, there was no difference in fresh total weight grown under White A, White B, and White B + FR, and the fresh leaf weight and dry total weight tended to be more when grown under White A. In ‘Yakiniku lettuce’, there was no dif­ ference in fresh total weight, stem weight, maximum leaf length, and dry total weight when grown under White A + FR, White B, and White B + FR. The root weight, stem weight, number of leaves, and dry total weight of plants grown under White A tended to Each value was indicated by mean±standard error (n=8). Different letters indicate significant differences by Tukey's multiple test with a significance level of 0.05. Table 2 ­ The growth difference in red lettuce cultivars by two kinds of white LED and FR light treatment Cultivars Kinds of LED Fresh total weight (g) Fresh leaf weight (g) Stem weight (g) Root weight (g) Maximum leaf length (cm) Main stem length (cm) Number of leaf SPAD Dry weight (g) Leaf lettuce red 1 White A 5.7±1.0 ab 3.7±0.3 b 1.5±0.3 b 0.4±0.0 b 13.3±0.6 18.6±0.4b 8.1±0.5 22.6±2.6a 0.31±0.05 b 2 White A+FR 4.3±0.6 b 3.0±0.4 b 1.3±0.2 b 0.3±0.1 b 13.0±0.4 19.4±0.3b 7.4±0.6 16.8±1.5b 0.23±0.03 b 3 White B 8.7±0.7 a 6.3±0.5 a 2.4±0.2 a 1.0±0.2 a 13.2±0.6 21.2±0.3ab 8.8±0.4 16.9±0.8b 0.50±0.07 a 4 White B+FR 4.3±0.2 b 2.8±0.8 b 2.0±0.5 ab 0.4±0.1 b 13.6±0.8 21.7±0.3a 7.4±0.5 18.2±1.3ab 0.38±0.07 a Red wave 5 White A 9.1±1.5 a 8.5±1.4 a 0.6±0.2 1.7±0.3 a 16.7±0.6 3.5±0.7b 6.7±0.3 17.2±2.0 0.50±0.08 a 6 White A+FR 9.0±1.5 a 8.1±1.3 a 0.8±0.2 1.2±0.2 a 17.3±0.7 4.7±0.9b 6.0±0.3 15.1±1.7 0.50±0.08 a 7 White B 7.0±1.3 ab 6.1±1.1 ab 0.9±0.3 0.9±0.1 ab 17.4±0.4 6.8±0.5a 6.5±0.5 17.8±3.1 0.36±0.06 ab 8 White B+FR 3.5±0.7 b 3.1±0.7 b 0.5±0.1 0.4±0.1 b 15.7±0.6 7.4±0.2a 6.1±0.4 12.8±1.2 0.20±0.04 b Bancyu sun 9 White A 6.8±1.1 b 6.2±1.0 b 0.6±0.1 b 0.7±0.2 b 16.6±1.2b 8.3±0.3ab 9.1±0.4 17.5±1.7 0.35±0.06 b 10 White A+FR 13.3±2.0 a 12.3±0.9 a 1.0±0.2 a 1.8±0.2 a 20.1±0.4a 6.4±0.3b 9.9±0.5 16.0±1.2 0.51±0.10 a 11 White B 6.5±1.2 b 5.8±1.2 b 0.8±0.1 ab 0.9±0.2 b 19.0±0.5ab 9.5±0.6a 9.5±0.6 14.4±1.7 0.30±0.04 b 12 White B+FR 11.3±0.9 a 10.5±0.8 a 0.9±0.1 a 1.6±0.1 a 20.8±0.7a 7.3±0.7b 10.4±0.5 16.9±1.5 0.54±0.05 a Sun bright 13 White A 10.1±0.7 b 8.9±0.6 b 0.9±0.0 b 1.2±0.2 b 15.6±0.5c 7.4±0.4b 9.6±0.3 15.2±1.3b 0.47±0.03 b 14 White A+FR 23.5±1.3 a 18.4±1.1 a 2.0±0.1 a 2.0±0.3 a 20.0±0.6b 9.5±0.7ab 9.6±0.3 17.0±2.4ab 0.62±0.03 a 15 White B 11.3±0.9 b 11.6±0.3 b 1.0±0.1 b 1.1±0.1 b 17.7±0.5 bc 8.7±0.8 b 9.9±0.4 15.9±2.0 b 0.47±0.07 b 16 White B+FR 22.7±3.7 a 15.7±0.9 a 2.6±0.2 a 1.1±0.2 b 26.1±0.9 a 11.5±0.6 a 9.1±0.4 24.0±1.4 a 0.59±0.05 a Fancy red 17 White A 9.1±0.6 a 9.3±0.4 ac 0.6±0.2 1.7±0.3 a 16.7±0.6 3.5±0.7 b 8.2±0.3 17.2±1.0 a 0.49±0.10 ab 18 White A+FR 8.9±0.6 a 9.5±0.3 a 0.8±0.2 1.2±0.2 a 17.3±0.7 4.7±0.9 b 8.3±0.5 15.1±0.7 ab 0.52±0.07 a 19 White B 3.5±0.7 b 3.1±0.7 b 0.5±0.1 0.4±0.1 b 15.7±0.6 7.4±0.2 a 8.0±0.4 12.8±1.2 b 0.20±0.03 c 20 White B+FR 6.6±1.1 c 5.3±0.8 c 0.6±0.1 0.9±0.2 a 17.4±0.4 4.9±0.6 b 8.2±0.3 17.8±1.1 a 0.36±0.06 b Red fire 21 White A 10.9±0.9 c 9.4±1.0 b 1.5±0.1 b 1.4±0.1 19.2±0.3 b 6.9±0.6 c 6.5±0.3 b 14.4±1.7 0.71±0.08 b 22 White A+FR 20.7±1.3 a 15.1±1.7 a 5.6±0.6 a 2.0±0.6 22.5±0.5 a 19.9±0.8 b 8.3±0.4 a 13.2±0.9 1.17±0.15 a 23 White B 17.9±0.8 bc 13.0±1.2 ab 4.9±0.6 a 2.0±0.4 22.1±0.6 a 22.3±1.3 ab 7.4±0.3 ab 14.9±1.1 0.91±0.11 ab 24 White B+FR 16.7±0.6 b 11.6±1.1 b 5.1±0.6 a 1.3±0.2 21.4± 0.6 a 24.7±1.6 a 8.5±0.3 a 14.3±0.7 0.93±0.10 ab Bancyu red fire 25 White A 9.5±0.6 a 8.6±0.4 a 1.0±0.3 a 1.5±0.3 19.1±0.8 ab 7.0±0.7 a 8.4±0.5 16.5±2.3 0.48±0.08 26 White A+FR 5.6±0.7 b 5.4±0.7 b 0.3±0.1 b 0.9±0.1 16.3±0.8 b 3.4±0.6 c 8.1±0.3 19.8±2.4 0.34±0.05 27 White B 8.5±0.6 a 8.0±0.5 a 0.6±0.1 ab 1.2±0.2 20.7±0.8 a 5.3±0.4 bc 8.5±0.7 15.5±2.0 0.47±0.03 28 White B+FR 6.0±0.9 ab 6.0±0.9 ab 0.2±0.0 b 1.0±0.1 15.3±0.8 b 3.1±0.4 c 8.6±0.4 18.8±2.6 0.38±0.06 Sun marino 29 White A 3.7±0.3 b 3.6±0.3 ab 0.1±0.0 b 1.1±0.2 10.0±0.3 b 2.5±0.6 8.1±0.3 14.1±1.4 b 0.20±0.02 b 30 White A+FR 6.3±0.8 a 5.5±0.9 b 0.3±0.1 a 0.8±0.2 11.8±0.7 ab 2.8±0.5 8.3±0.5 17.0±1.0 a 0.34±0.03 a 31 White B 4.2±0.6 b 3.6±0.7 ab 0.2±0.0 a 0.8±0.2 12.1±0.3 a 2.5±0.3 7.8±0.3 17.9±1.1 a 0.33±0.05 a 32 White B+FR 2.7±0.2 b 2.7±0.3 a 0.4±0.1 a 0.7±0.1 10.8±0.7 ab 3.5±1.3 7.5±0.3 12.5±1.4 b 0.24±0.06 ab Calbee red 33 White A 13.2±1.5 a 8.5±0.9 a 1.0±0.4 b 1.3±0.2 ab 16.5±0.4 b 5.9±1.2 c 7.7±0.2 19.8±0.9 a 0.73±0.10 a 34 White A+FR 13.1±0.9 a 8.7±0.5 a 2.9±0.2 a 1.6±0.2 a 20.3±0.6 a 16.2±0.6 a 7.8±0.3 18.5±0.5 ab 0.64±0.04 a 35 White B 4.6±0.7 b 4.0±0.6 b 1.7±0.3 b 0.9±0.1 ab 17.6±0.4 b 13.8±0.5 b 6.7±0.5 19.4±1.2 ab 0.26±0.03 b 36 White B+FR 7.5±0.6 b 4.6±0.5 b 1.7±0.3 b 0.6±0.1 b 18.0±1.4 ab 17.7±0.7 a 6.6±0.3 16.0±1.14 b 0.38±0.06 b Kamimaeda et al. ‐ Effect of EOD‐FR light under white LEDs in lettuces 235 decrease, and a significant difference was observed in the stem weight and dry total weight. Although the total light intensity was higher in White A + FR and White B + FR than in White A and White B, White B + FR showed no significant decrease in fresh leaf weight and dry weight only in ‘Fancy green’ grown under white B, suggesting that FR LED had little effect on the total light intensity in this experiment. However, it would be necessary to investigate the effects of similar total light intensity with and with­ out FR irradiation in the future. Principal component analysis was conducted to divide the cultivars into red lettuce cultivars and green lettuce cultivars to make it easier to under­ stand the tendency. The average values of various traits for each LED treatments for each cultivar were used, and the parameters are shown in Tables 4 and 5. The contribution rates of the first principal compo­ nents of the red lettuce cultivars and green lettuce cultivars were 47.34% and 38.23%, respectively. The first principal component in red lettuce cultivars showed a positive factor loading for all traits except the main stem length, and a negative factor loading for only the main stem length. The first principal component in green lettuce cultivars showed a positive factor loading for fresh total weight, fresh leaf weight, stem weight, maximum leaf length, and main stem length, and a negative factor loading for root weight, number of leaves, SPAD, and dry total weight. Furthermore, the second main component in red lettuce cultivars showed a positive factor loading for stem weight and main stem length, and a nega­ tive factor loading for the others. The second main component for green lettuce cultivars showed a posi­ tive factor loading for fresh total weight, and fresh Table 3 ­ The growth difference in green lettuce cultivars by two kinds of white LED and FR light treatment Table 4 ­ Eigen value, contribution and factor loading of 1st, 2nd and 3rd principal components in red leaf lettuce culti­ vars Each value was indicated by mean±standard error (n=8). Different letters indicate significant differences by Tukey's multiple test with a significance level of 0.05. Cultivars Kinds of LED Fresh total weight (g) Fresh leaf weight (g) Stem weight (g) Root weight g) Maximum leaf length (cm) Main stem length (cm) Number of leaf SPAD Dry weight (g) Summer green 37 White A 14.4±0.8 a 12.2±0.6 a 2.1±0.4 ab 1.7±0.2 18.1±0.6 9.5±0.8 b 14.8±1.3 32.2±3.2 0.42±0.09 ab 38 White A+FR 12.7±1.1 b 8.6±1.0 b 2.3±0.3 ab 1.6±0.2 18.3±0.6 10.6±0.5 b 15.3±0.9 39.2±3.0 0.31±0.05 b 39 White B 12.4±0.6 b 10.4±0.4 b 2.0±0.2 b 1.6±0.4 17.7±0.8 11.6±0.5 b 16.1±1.1 36.3±1.9 0.33±0.08 ab 40 White B+FR 13.8±1.1 ab 12.1±0.5 a 3.1±0.4 a 1.6±0.5 19.3±0.3 16.3±1.1 a 14.1±1.0 28.4±4.5 0.63±0.10 a Fancy green 41 White A 14.1±0.4 b 11.8±0.7 b 1.6±0.1 ab 1.0±0.1 b 19.3±0.5 b 10.4±0.4 a 10.0±0.4 16.4±1.5 b 0.49±0.04 b 42 White A+FR 17.5±1.3 a 15.2±0.4 a 1.3±0.2 bc 1.5±0.3 ab 23.5±0.7 a 6.4±0.4 b 9.9±0.6 24.9±1.3 a 0.57±0.06 a 43 White B 19.5±0.7 a 16.6±0.7 a 1.9±0.1 ab 1.8±0.2 ab 24.7±0.7 a 7.3±0.5 b 9.1±0.7 27.8±2.7 a 0.63±0.07 a 44 White B+FR 10.4±0.7 c 9.2±0.7 b 0.7±0.1 c 2.1±0.5 a 19.7±0.6 b 5.7±0.6 b 9.8±0.3 30.3±1.4 a 0.49±0.05 b Green wave 45 White A 6.2±0.4 a 3.9±0.9 2.3 ±0.5 0.6±0.1 a 21.7±0.8 b 13.5±0.5 7.0±0.5 24.3±2.8 0.57±0.11 46 White A+FR 4.4±0.5 b 2.7±0.3 1.7 ±0.2 0.4±0.1 b 21.5±1.3 b 13.4±0.5 6.7±0.6 22.9±0.9 0.47±0.06 47 White B 5.1 ±1.1 ab 2.8±0.7 2.3±0.5 0.6 ±0.1 a 25.9±1.4 a 13.8±0.6 7.0±0.3 22.3±1.1 0.50±0.09 48 White B+FR 5.1 ±0.6 ab 3.0±0.4 2.1± 0.3 0.4±0.1 b 26.8±1.6 a 14.3±0.5 6.6±0.3 22.3±1.1 0.53±0.03 Yakiniku lettuce 49 White A 2.5±0.4 b 1.8±0.3 b 0.3±0.1 b 0.4±0.1 b 10.3±0.5 b 7.4±0.6 b 6.3±0.5 18.6±1.3 a 0.16±0.02 b 50 White A+FR 4.1±0.3 a 3.4±0.3 a 0.7±0.1 a 0.7±0.1 a 12.0±0.4 ab 9.1±0.5 ab 6.5±0.4 20.8±1.9 a 0.39±0.04 a 51 White B 3.4±0.6 ab 2.0±0.3 b 0.7±0.1 a 0.3±0.1 b 13.7±0.8 a 11.1±0.9 a 6.6±0.6 14.8±1.5 b 0.31±0.01 a 52 White B+FR 4.0±0.2 a 3.3±0.2 a 0.7±0.1 a 0.5±0.1 ab 12.9±0.3 a 10.3±0.5 a 6.8±0.6 15.7±1.2 ab 0.32±0.04 a Characteristics Component No. 1 2 3 Fresh total weight (g) 0.460 ­0.011 0.049 Fresh leaf weight (g) 0.458 ­0.027 ­0.028 Stem weight (g) 0.327 0..541 0.179 Root weight (g) 0.411 ­0.154 ­0.234 Maximum leaf length 0.333 0.281 0.425 Lengh of main stem (cm) ­0.038 0.648 ­0.124 No. of leaves 0.266 ­0.347 ­0.332 SPAD 0.071 ­0.385 0.738 Dry weight (g) 0.337 ­0.051 ­0.244 Eigen value 3.287 1.423 0.868 Contribution 47.34% 20.49% 12.51% Cumulative contribution 47.34% 67.84% 80.34% 236 Adv. Hort. Sci., 2023 37(2): 231­239 leaf weight, stem weight, root weight, maximum leaf length, SPAD, and dry total weight, and a negative factor loading for the others. The cumulative contri­ bution rates of the first and second principal compo­ nents were 67.84% and 70.13% in the red and green lettuce cultivars, respectively. Principal component analysis was performed because the values were considered to be effective. For red lettuce cultivars, the scatter diagram of the types of LEDs and each cultivar for the first (Z1) and second main components (Z2) showed that the fresh total weight, fresh leaf weight, stem weight, root weight, and dry total weight in ‘Red wave’, ‘Bancyu sun bright’, ‘Sun bright’, ‘Fancy red’, ‘Red fire’, ‘Sun Marino’ and ‘Calbee red’ grown under White A + FR was higher (Fig. 2). In addition, it showed an opposite tend for the fresh total weight, fresh leaf weight, and dry weight in ‘Leaf lettuce red’ and ‘Bancyu red fire’ grown under white B. Also, for ‘Bancyu sun bright’, ‘Sun bright’, ‘Fancy red’, and ‘Calbee red’ grown under White B, the fresh total weight, fresh leaf weight, and dry weight tended to be less. While the maximum leaf length for these cul­ tivars grown under White B tended to be less, the main stem length tended to be more. On the other hand, for green lettuce cultivars, ‘Summer green’ grown under White A + FR and White B, ‘Yakiniku let­ tuce’ grown under White A, and ‘Green wave’ grown under White A + FR showed a tendency for the fresh weight, fresh leaf weight, stem weight, and dry weight and the maximum leaf length to be lower as shown in the scatter diagram for the first and second main components (Fig. 3). 4. Discussion and Conclusions The fresh total weight, fresh leaf weights, and dry total weight cultivated under White A and B with or without FR LED in lettuce cultivars tested in this study increased or decreased. It was considered that the Fig. 2 ­ The scatter diagram in Z1­Z2 plane nine characteristics in red lettuce cultivars arranged by the principal compo­ nent analysis. ■: White A irradiation，●: White A + FR irradiation，×: White B irradiation，△: White B + FR irradiation *Numbers were shown in Table 2. Fig. 3 ­ The scatter diagram in Z1­Z2 plane nine characteristics in red lettuce cultivars arranged by the principal compo­ nent analysis. ■: White A irradiation，●: White A + FR irradiation，×: White B irradiation，△: White B + FR irradiation. * Numbers were shown in Table 3. Table 5 ­ Eigen value, contribution and factor loading of 1st, 2nd and 3rd principal components in green leaf lettuce cul­ tivars Characteristics Component No. 1 2 3 Fresh total weight (g) 0.354 0.418 0.059 Fresh leaf weight (g) 0.285 0.442 ­0.015 Stem weight (g) 0.473 0.188 0.143 Root weight (g) ­0.101 0.462 0.330 Maximum leaf length 0.449 0.004 ­0.227 Lengh of main stem (cm) 0.427 ­0.256 0.196 No. of leaves ­0.030 ­0.189 0.875 SPAD ­0.357 0.380 ­0.041 Dry weight (g) ­0.216 0.368 0.095 Eigen value 2.752 2.297 0.890 Contribution 38.23% 31.93% 12.37% Cumulative contribution 38.23% 70.13% 82.5% Kamimaeda et al. ‐ Effect of EOD‐FR light under white LEDs in lettuces 237 type of LED irradiated in the photoperiod was deeply related to the effect of the FR irradiated in the dark period, as this phenomenon was similar to the elongation of the main stem (Tables 2 and 3). For the cultivars ‘Leaf lettuce red’, ‘Bancyu red fire’, ‘Calbee red’, and ‘Green wave’, it was considered better to use only white LEDs without FR treatment because white LED irradiation with FR LED did not increase leaf weight and the running cost was more. However, white LEDs that are generally sold have different wavelengths depending on the manufacturer, and hence this inference may not apply to all white LEDs. In general, it has been reported that FR light treatment promotes the elongation of the main stem or hypocotyl in cucumber (Cucumis sativus L.), lily (Lilium longiforum Thumb.), and chrysanthemum (Chrysanthemum moriforlium Ramat.) (Blom et al., 1995; Xiong et al., 2002; Hisamatsu et al., 2008). However, in Brassicaceae, Akutsu et al. (2016) reported that komatsuna and red mustard (B. juncea) were unable to extend the main stem, while pak choi and ‘shimana’ (a cultivation of B. juncea) easily extended the main stem regardless of the cultivation period and the light intensity of FR LEDs; thus, the effect differed depending on the plant species and cultivars being treated with the FR LED. Furthermore, the effect of FR treatment on leaf area and main stem in komatsuna and pak choi differed depending on the variety (Akutsu et al., 2017). The elongation of the main stem causes quality deterioration in terms of appearance and taste in leafy vegetables such as lettuce. The main stem was elongated regardless of the FR treatment for all lettuce cultivars tested in this experiment. However, it was found that the relationship between the main stem elongation and FR treatment can be divided into several patterns regardless of whether they were green or red lettuce cultivars. Under White A irradiation, FR treatment did not promote the main stem elongation in ‘Leaf lettuce red’, ‘Red wave’, ‘Fancy red’, ‘Sun marino’, ‘Summer green’, ‘Green wave’, and ‘Yakiniku lettuce’, while it promoted the main stem elongation in ‘Sun bright’, ‘Red fire’, and ‘Calbee red’. In addition, FR treatment suppressed the main stem elongation in ‘Bancyu sun bright’, ‘Bancyu red fire’, and ‘Fancy green’. On the other hand, under White B irradiation, FR treatment did not have an effect on the main stem elongation in ‘Leaf lettuce red’, ‘Red wave’, ‘Bancyu sun bright’, ‘Red fire’, ‘Sun marino’, ‘Fancy green’, ‘Green wave’, and ‘Yakiniku lettuce’, while it promoted the main stem elongation in ‘Sun bright’, ‘Calbee red’ and ‘Summer green’. In addition, FR treatment suppressed the main stem elongation in ‘Fancy Green’ and ‘Bancyu red fire’. Thus, it was considered that the relationship between FR irradiation and main stem elongation depends on the variety and cultivar. In addition, some cultivars such as ‘Fancy red’, ‘Red fire’, ‘Summer green’ and ‘Fancy green’, which showed an increase or a decrease in the main stem elongation after FR treatment, depending on if they were cultivated under White A or White B irradiation. There are also reports that FR treatment did not have any effect on main stem elon­ gation in lettuce (Mickens et al., 2018; Lin et al., 2020). Therefore, it was found that the effect of FR treatment on the main stem elongation differs depending on the wavelength of the LED irradiated in the photoperiod and on the cultivars. On the other hand, some cultivars such as ‘Sun bright’, ‘Sun mari­ no’, and ‘Fancy green’, which an increase in SPAD after FR treatment depending on if they were cultivated under White A or White B irradiation, there was no effect of FR irradiation on SPAD in the other cultivars investigated in this experiment (Table 2 and 3). Thus, it was considered that no relationship between FR irradiation and SPAD depends on the variety and cultivar. Furthermore, based on the results of the main component analysis for fresh and dry weights, the fresh total weight and the fresh leaf weight increased as the Z1 axis (the first principal component) became positive in all lettuce cultivars tested in this experi­ ment, and the dry weight increased as the Z2 axis (the second principal component) became positive in red lettuce cultivars and as the Z2 axis became nega­ tive in green lettuce cultivars. Under White A LED irradiation, fresh total weight and fresh leaf weight were increased in all red lettuce cultivars except ‘Leaf lettuce red’ and ‘Bancyu red fire’ on treatment with FR LED, while the fresh total weight and fresh leaf weight were increased in only ‘Fancy green’ in green lettuce cultivars. This suggests that the effect of FR treatment cultivated under White A irradiation may be higher in red lettuce cultivars than in green lettuce cultivars. On the other hand, under White B irradia­ tion, fresh total weight and fresh leaf weight were increased in only ‘Bancyu sun bright’ and ‘Sun bright’ of red lettuce cultivars and in ‘Summer green’ and ‘Yakiniku lettuce’ of green lettuce cultivars on the treatment FR LED. This suggests that the effect of FR treatment when cultivated under White A may be higher than when cultivated under White B in red let­ Adv. Hort. Sci., 2023 37(2): 231­239 238 tuce cultivars. Therefore, it is necessary to select let­ tuce cultivars that match the type of white LED used as a source of light in the photoperiod, and depend­ ing on the lettuce cultivar used, select whether to treat with FR LED. The main stem, which is unsuitable for sale was remarkably elongated under the two kinds of white LEDs either with or without FR treatment for the 13 leaf lettuce cultivars tested in this experiment. In general, white LEDs have different intensity, spec­ trum, and shade by adjusting the monochromatic emission of red, yellow, green, and blue (Chang et al., 2012), as shown in white A and B, respectively, used in this experiment. Also, In lettuce, the effect of FR light is clearly intensity­dependent, and the intensity required for maximum response depends on the trait (Zou et al., 2021). Furthermore, the effect of FR light has been found to depend on the type of photosyn­ thetic photon flux density (PPFD, 400­700 nm) radia­ tion and light intensity (Meng and Runkle, 2019). 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