Growth and Quality of Leafy Sweet Potatoes Grown Hydroponically under Different EC Conditions in a Plant Factory

Leafy sweet potato [Ipomoea batatas (L.) Lam] is developed primarily for its leaves rather than its roots, which are rich in secondary metabolites such as lutein. As limited studies have explored the production of leafy sweet potato in a plant factory with artificial lighting (PFAL), this study aimed to investigate the growth and quality responses of leafy sweet potato to different electrical conductivity (EC) levels in the nutrient solution and to determine the optimal EC for hydroponic cultivation in a PFAL. Two cultivars, ‘Tongchaeru’ and ‘Suioh’, developed for leaf consumption in Korea and Japan, respectively, were used. Controlled environmental conditions were used, specifically an air temperature of 25/22°C, relative humidity of 65 ± 5%, light intensity of 250 µmol ∙m^-2∙s^-1, and a photoperiod pf 16 h in a plant factory that used white LEDs. Nutrient solutions with four different EC levels (1.0, 2.0, 3.0, and 4.0 dS·m^-1) were supplied to leafy sweet potatoes. At 35 days after transplanting tissue-cultured seedlings, the EC 2.0 dS·m^-1 treatment resulted in the highest overall growth in both cultivars. The anthocyanin content in ‘Tongchaeru’ was highest at EC 1.0 dS·m^-1, followed by EC 4.0 dS·m^-1, while in ‘Suioh’, it was highest at EC 4.0 dS·m^-1. The lutein content showed a substantial increase at EC 4.0 dS·m^-1 in both cultivars. Intumescence symptoms were observed under all EC treatments and in both cultivars, with greater severity in ‘Suioh’. In leaves exhibiting intumescence, stomatal conductance and the anthocyanin content were lower than in normal leaves, whereas the lutein content increased under high EC conditions. These results suggest that an EC of 2.0 dS·m^-1 is optimal for biomass production, while EC 4.0 dS·m^-1 is favorable for the accumulation of functional compounds. Further studies are needed to optimize hydroponic strategies for simultaneously enhancing the yield and phytochemical accumulation. This study provides a foundational basis for developing production systems for leafy sweet potato in PFALs.