Evaluate the effects of winter stress(freezing and snow) on some morphological and physiological reactions of commercial citrus in Tonekabon area

Citrus is a subtropical crops, therefore susceptible to freeze stress. This fruit tree has a different response to freeze stress according to the genotype and environment climate. Therefore, to evaluate the damage of freeze stress (winter 2014) on commercial citrus of Tonekabon area (Thomson Navel orange, Satsuma and Page mandarin) the morphological and physiological responses are assayed based on randomized complete block design (average was evaluated by LSD).The results showed that freeze stress can reduce chlorophyll (a, b, total) and leaf water content (p≤ 0.01). Based on data the Thomson Navel orange had the greatest reduction in these parameters. Therefore, the lipid peroxidation (1.48 µmol/g FW) and electrolyte leakage (53.06%) of Thomson Navel orange was higher than the other subjects in this study. The laboratory analysis showed that in the Satsuma mandarin prolin content (30.3 mg/g FW) and anti-oxidant capacity (73.44%) of leaves was higher than the other cultivars. But the assessment of fracture branches, most of the losses was recorded in the Page mandarin.In general, we can suggest that the Satsuma mandarin was more persistent than the other two cultivars of this study, was best tolerant to freezing stress because of lowest EC parameter in winter and best flowering in spring.