Possibility of Harvesting June-bearing Strawberries in a Plant Factory with Artificial Light during Summer and Autumn by Re-using Plants Cultivated by Forcing Culture

In Japan, June-bearing strawberry cultivars are commercially produced from November to May in forcing greenhouses (Yoshida and Nishimoto, 2020), and June to October is off-season due to their physiological characteristics (Yamasaki, 2013; Yamazaki and Yano, 2016). However, fresh strawberry fruits are in demand all year round for eating raw or topping cakes (Yanagi, 2017), and approximately, 3,000 tons are imported annually from the United States to fill the supply gap (Tokyo Customs, 2014; Ministry of Agriculture, Forestry and Fisheries, 2019). As the appearance and taste of the imported fruits are not highly appreciated in the Japanese market, in addition to concerns on pesticide application and post-harvest treatments abroad, domestically produced strawberries are preferred (Imada, 2007). Therefore, everbearing strawberries are planted in cold areas for off-seasons to increase the production of domestic strawberries in summer and autumn (Yamazaki, 2015; Ohta and Yasuba, 2019). On the other hand, as confectioneries claim that everbearing strawberries have a poorer taste than that of June-bearing strawberries (Shibuya, 2010; Hamano et al., 2020), they want a year-round stable supply of June-bearing strawberries. In the plant factory with artificial light (PFAL), leafy vegetables such as lettuce grow rapidly and yield a yearround high under low-intensity fluorescent and LED lights, with little to no pesticide application (Yoshida et al., 2016), and fresh leafy vegetable production in PFALs is increasing (Goto, 2012). However, fruits, including strawberries, require stronger light intensity to facilitate photosynthesis (Shimizu et al., 2011; Maeda et al., 2016; Furuyama et al., 2017). In addition, the running cost of PFALs for more than 2 months of nursery period will increase, with no strawberry production (Fushihara, 2005). The most important difference between fruit and leafy vegetable cultivation in PFALs is that, the former needs modified day length and temperature in each stage of development for fruit production (Sønsteby and Heide, 2006; Hytönen and Kurokura, 2020). Off-season strawberry production of June-bearing cultivars in PFALs has been studied in Japan (Suwa and Nakajima, 2014), and a patent has been applied for cultivation methods (Nisshinbo Holdings Co., Ltd., 2013). However, production of high-quality strawberries in PFALs is uncommon because of insufficient fruit yield to meet the operational costs (Yoshida et al., 2013). In recent years, PFALs have been developed for