Effect of Light Quality on Physiological Disorder, Growth, and Secondary Metabolite Content of Water Spinach (Ipomoea aquatica Forsk) Cultivated in a Closed-type Plant Production System

Abstract

Light quality is a critical factor that affects plant quality, including phytochemical accumulation and marketable characteristics, in closed-type plant production systems. The purpose of this study was to determine the appropriate light quality for production of good quality water spinach in terms of its appearance and accumulation of phytochemicals in an artificial environment. Plants were hydroponically cultured under five different light quality conditions: red, blue, green, red and blue (as a control), and red and blue with far red at a photosynthetic photon flux density of 200 µmol·m-2·s-1 for 14 days after transplantation. Shoot (stem and leaf) fresh weights (FW) under red-containing light conditions increased more than 39.7% compared to that under monochromatic blue light, and monochromatic red light produced significantly higher stem FW but lower leaf FW compared to that under blue-containing light conditions. Monochromatic blue light significantly increased the antioxidant activity capacity in leaves and stems more than 210.0% compared to other treatments. However, blue-containing light significantly stimulated physiological disorder (intumescence injury) in stems and suppressed stem elongation compared to monochromatic red or green light. Monochromatic red light reduced the number of intumescent lesions by 95.8% and enhanced stem elongation compared to control. These findings suggest that red-rich light promotes growth of water spinach with less intumescence.