Effect of Different PPFDs and Photoperiods on Growth and Yield of Everbearing Strawberry ‘Elan’ in Plant Factory with White LED Lighting

In recent years, plant factory with artificial light (PFAL) has become popular in Japan (Goto, 2012). The important characteristics of the plants suitable for PFAL are as follows: (1) the plant’s height must be relatively low, (2) the time from sowing to harvesting or coming to maturity should be short, and (3) the plant should be able to grow even at low-light intensity. Therefore, previous studies related to vegetable production in PFAL often used leafy vegetables and seedlings (Kozai, 2018). However, strawberry plant has lower light requirement and lower plant height than tomato and cucumber, so it can be cultivated in a multi-layer system in PFAL. In addition to this, the unit price of strawberry fruits is higher than that of leafy vegetables. Hence, it is considered to be suitable for strawberry production in PFAL (Yoshida et al., 2013). In recent PFALs, light emitting diode (LED) is usually used as the light source. LEDs have several advantages over fluorescent lamps. For example, the quality of light can be controlled by adjusting the arrangement of the emitting element, the lifetime is long, the amount of light is stable for a long time, light emits no heat, and so on. Concerning the quality of light, many experiments using LEDs have been conducted in environmentally controlled closed-type chambers. Among them, a mixture of red and blue has been reported to be efficient for plant cultivation (Nhut et al., 2003; Shin et al., 2008). Moreover, Lin et al. (2013) reported that the addition of white LEDs to redblue mixed LEDs promoted lettuce growth. Regarding studies on strawberries, though there have been studies conducted on the effect of light quality, that is, red, blue, or red-blue mixed on strawberry plants in a closed plant factory (Choi et al., 2015; Yoshida et al., 2016), there is limited information on the suitability of white LEDs in strawberry production. Considering strawberry production in PFAL, everbearing varieties may be more suitable than June-bearing varieties (Yoshida et al., 2013). June-bearing varieties require low temperature with short-day condition for flower bud differentiation, whereas everbearing varieties require longday condition for the same. Thus, the growth and continuous flowering of everbearing varieties can be simultaneously promoted under long-day condition. It is considered to lead to shortening of the seedling period. For this reason, several studies on photoperiod using everbearing varieties have been carried out and continuous lighting with blue light was efficient for running cost and initial cost (Yoshida et al., 2012; Yoshida et al., 2016), however, there is limited information about how much light (daily light integral; DLI), that is, the product of photosynthetic photon flux density (PPFD) by day’s length, the strawberry actually needs under continuous lighting. Therefore, in this experiment, we set various DLIs by combining different photoperiods and PPFDs, and evaluated the continuous light with white LED.