Evaluation of freezing tolerance of sugar beet (Beta vulgaris L.) cultivars under controlled conditions

In order to determine the freezing tolerance of sugar beet (Beta vulgaris L.) cultivars under controlled environment, a factorial experiment was conducted based on completelyrandomized design with three replications at College of Agriculture, Ferdowsi University ofMashhad. In this research, eight cultivars including Rasoul, Shirin, IC, 7233 (nationalcultivars), Afshari, Paolina, Rhizofort and Laetitia (foreign cultivars), were exposed to eightfreezing temperatures (0, -2, -4, -6, -8, -10, -12 and -16 °C). Plants were grown under natural environment until 4- to 5- leaf stage and were transferred to thermo-gradient freezer to apply freezing temperatures at early spring. Survival percentage, dry weight, SPAD reading, 50% lethal temperature (LT50) and the temperature for 50% dry matter reduction (RDMT50) of the samples were determined at the end of recovery period (3 weeks after applying freezing temperatures). Results showed that freezing temperature and cultivar significantly influenced the survival percentage, dry weight and SPAD reading (p≤0.01). Decreasing temperature below -8 °C significantly decreased the mean survival percentage of cultivars, while significant reductions of dry weight and SPAD reading comparing with the control (0 °C) were started at temperatures -2°C downward. Moreover, LT50 and RDMT50 of examined cultivars were significantly different (p≤0.01), so that Paolina, Laetitia and Shirin cultivars with LT50 of -11.5 °C and Afshari with LT50 of -9.1 °C had the highest and lowest freezing tolerance, respectively. Afshari showed the highest amount of RDMT50 (= -7.7 °C) amongst beet cultivars. It seems that according to good correlation between RDMT50 and LT50 (r=0.83**), may indicate that using this index might be used for evaluation of freezing tolerance among sugar beet cultivars.