Evaluation of Invasive plant Centaurea balsamita cold Acclimated in the falling to freezing stress

In order to evaluate the effect of freezing stresses on invasive plant of Centaurea balsamita, an experiment was performed as factorial, based on completely randomized design with five replications at Ferdowsi University of Mashhad, Faculty of Agriculture during 2014. In this experiment Centaurea balsamita after their period of cold acclimation in the falling exposed to seven freezing temperatures (0, -3, -6, -9, -12, -15 and -18 °C). Potted plants were grown in natural conditions and maintained for acclimation, until 2-4 and 4-8 leaf stages and then, the plants were placed in a thermogradian freezer in different chilling and the freezing temperature (FT) regimes. The cytoplasm membrane stability of Centaurea balsamita was evaluated using electrolyte leakage; then the lethal temperature of 50% of samples was determined based on leakage percentage (LT50el). Survival percentage was evaluated by counting the number of live plants in each pot. Then, at the end of the recovery period, the lethal temperature for 50% of survival percentage (LT50su) and reduction temperature for 50% of dry weight (RDMT50) were determined (three weeks after the application of freezing treatment). According to the results of the first experiment, temperature reduction from -12 °C to -15 °C leads to significant increase (P≤ 0.05) in electrolyte leakage of Centaurea balsamita. In addition, temperature reduction from -9 °C to -12 °C results in significant decrease (P≤ 0.05) in survival percentage and biomass of Centaurea balsamita. The results showed that LT50el, LT50su and RDMT50 of cold acclimated Centaurea balsamita in fall conditions were -13.2 °C, -126 °C and -11.8 °C, respectively