Evaluation of physiological and biochemical responses of some ornamental citrus varieties under low temperature stress

Low temperature stress is one of the most important abiotic environmental stresses that affect the growth and yield of ornamental plants. In order to investigate of some physiological and biochemical indices of four varieties of ornamental citrus used in urban landscapes under low temperature stress conditions, a factorial experiment in a completely randomized design with three replications was conducted in the Citrus and Subtropical Fruits Research Center of Ramsar in 2015. Treatments were included the temperature with four levels (3, 0, -3 and -6˚C) and four varieties of ornamental citrus including (Kumquat, Fingered citron, Calamondin and Limequat). Results showed that amounts of electrolyte leakage, water soaking, prolin content, antioxidant capacity, lipid peroxidation and superoxide dismutase activity were increased significantly by reducing of temperature, while chlorophyll a and total chlorophyll contents were decreased. Accordingly, the lowest leaf water soaking (20.92 Percent) and electrolyte leakage (30.81 Percent) amount, which are destructive indices, were showed in kamquate. Also total chlorophyll amount (2.21mgr/grFW), antioxidant capacity (60.61 Percent) and superoxide dismutase activity (26.53 IU/gr FW) that are tolerability indices were more evident in this variety. In general, Kumquat could tolerate the freezing stress up to -3°C by increasing of some indices such as proline, soluble sugars, antioxidant capacity and superoxide dismutase activity.