Impact of Cold Stress on Physiological Responses and Fruit Quality of Shiranuhi Mandarin in Response to Cold Conditions

Abstract

We identified the minimum temperature limits to ensure Shiranuhi mandarin growth and fruit quality and provided overwintering temperature management guidelines. Expanded polystyrene panels with air conditioners were exposed to −1, −3, and −5 °C in the greenhouse for 15 h to determine the overwintering temperature. Leaves and fruits were analyzed at intervals for physiological response, fruit quality, and aromatic components. The low temperature treatment groups showed 1.3 to 1.4 times increased malondialdehyde content in leaves and 1.1 to 1.3-fold higher electrolyte linkage rates in the −5 °C treatment group alone. The sugar/acidity ratio was 1.1 to 1.3 times higher in the −5 °C treatment than in the control due to rapid acid reduction. The fruit firmness and citrus color index decreased notably after 21–28 days of treatment. Ascorbic acid content significantly decreased 17.3%–41.1% at −5 °C. Among the aromatic compounds, decanal levels notably increased with −5 °C treatment; −5 °C cold treatment notably affected oxidative stress in leaves and the sugar/acid ratio, ascorbic acid content, and aromatic compounds in fruits. If prolonged exposure to temperatures <−5 °C is expected, preharvest heating facilities are critical. We recommend maintaining greenhouse temperatures >0 °C during fruit growth and >−3 °C after harvest as the minimum temperature to preserve fruit set and quality.