Long-term Elevated Temperature Affects the Growth and Quality of ‘Shiranuhi’ Mandarin Grown in a Green House

BACKGROUND: The mean annual temperature of the Korean Peninsula will continue to rise due to global warming. ‘Shiranuhi’ mandarin—a late-harvest cultivar —is primarily cultivated in plastic greenhouses where high temperatures cannot be directly avoided. Therefore, growth and fruit quality changes under elevated temperatures must be investigated. METHODS AND RESULTS: Elevated temperatures were divided into three groups [2°C (T-I), 4°C (T-II), and 6℃ (T-III) above the ambient temperature] during the 2019-2020 season. Mean temperatures were 17.1℃, 18.6 ℃, and 20.2℃ in T-I, T-II, and T-III, respectively. The bud bursts in T-II and T-III were earlier than that in T-I at 7 days and 11 days, respectibely. And the full blooms in T-II and T-III were earlier than that in T-I at 11 days and 23 days, respectively. Fruit size significantly increased with increased temperature. The citrus color index in the coloring phase markedly differed across treatments. Fur-ther, total soluble solid and acid contents markedly chan-ged with temperature rise but the sugar-to-acid ratio did not. Sucrose content tended to decrease with increase in temperature, but citric acid content remained unaffected. CONCLUSION(S): Elevated temperature accelerated plant growth and development but delayed rind color development in ‘Shiranuhi’ mandarin. Therefore, rise in ambient temperature by >4.6°C may negatively affect yield and fruit quality.