Effect of air temperature on growth and phytochemical content of beet and Ssamchoo

Abstract

The consumption of leaf vegetables has been steadily increasing in Korea. Leaf vegetables are used for “Ssam (vegetable wrap-up), eaf vegetables has been steadily increasing in Korea. Leaf vegetables are used for asoned condiments inside several layers of young vegetable leaves. This study investigated the effect of air temperature on the growth and phytochemical contents of beet (Beta vulgaris L.) and Ssamchoo (Brassica lee L. ssp. namai) grown in a closed-type plant factory system where fluorescent lamps were used as an artificial light source. Seeds of beet and Ssamchoo were sown in a peat-lite germination mix. The roots of 20-day-old seedlings were washed, and the seedlings were planted on a styrofoam board and grown in hydroponic beds for 25 days under fluorescent light. Plants were exposed to one of three different air temperature regimes (20, 25 and 30°C during the day combined with 18°C during the night), which were monitored with a sensor at 30 cm above the plant canopy. Increased plant height and leaf area were observed in beet at 25°C and 30°C compared to 20°C. For Ssamchoo, the greatest plant height, leaf area, fresh weight and dry weight were obtained at 20°C. Ascorbic acid content of beet and Ssamchoo leaves were highest at 30°C. In beet, total polyphenol and flavonoid contents were higher at 20°C (42.4, 197.0 mg･g-1DW) and 25°C (46.9, 217.0 mg･g-1DW) than 30°C (22.4, 88.0 mg･g-1DW). In Ssamchoo, total polyphenol and flavonoid contents were also higher at 20°C (79.2, 268.2 mg･g-1DW) and 25°C (66.3, 258.3 mg･g-1DW), respectively, than 30°C (53.7, 134.7 mg･g-1DW). Hence, the optimum temperature appears to be 20°C for growing both beet and Ssamchoo in a closed-type plant factory system with fluorescent light.