Evaluation of freezing tolerance of sweet william (Dianthus barbatus) under controlled conditions

The aim of this experiment was to study the freezing tolerance of Dianthus barbatus under controlled conditions and was arranged as a completely randomized design with three replications. After sowing and growing plants in the bed in mid of summer to early autumn, at mid autumn (after hardening under natural conditions), plants were placed in the thermo-gradient freezer at the 7-8 leaf stage with 12 freezing temperatures (0,-2,-4,-6,-8,-10,-12,-14,-16,-18,-20,-22 oC). Cell membrane stability after freezing was assessed through electrolyte leakage (EL), survival percentage and re-growth of the plants after 3 weeks in cold frame were measured by counting the number of plants and determining their proportion to the number of plants before freezing and measuring the dry matter, height and number of branches. The results indicated that the effect of different freezing temperatures were significant at all plant characteristics (P≤0.05). With decreasing the temperature, EL increased significantly (P≤0.05) and reach to the maximum at -22°C. Survival percentage of plants did not affect until -18°C, but all plants were died at -22°C. The 50% of plants lethal temperature (LT50) of samples according to the EL and survival were -21 and -20.3°C, respectively, while the 50% reduced dry matter temperature (RDMT50) was -16°C.