Evaluation of freezing stress in withania (Withania coagulans‏ ‏Dun) under controlled ‎conditions

In order to investigate freezing tolerance in withania under controlled conditions, a completely randomized design was carried out with four replications and nine temperature treatments (0, -3, -6, -9, -12, -15, -18, -21 °C and control treatment 25°C). Studied traits included electrolyte leakage, cell membrane stability, proline content, chlorophyll fluorescence, chlorophyll degree, 50% lethal temperature based on survival (LT50su) and 50% lethal temperature based on electrolyte leakage (LT50el). Results showed that the effect of freezing stress on all traits was significant at a probability of one percent. Electrolyte leakage showed increased and cell membrane stability decreased. The leaf chlorophyll fluorescence decreased with increasing freezing stress, so that it reached its lowest point at temperatures below -9°C. Chlorophyll content index was also affected by the effect of freezing stress, which decreased at a steep slope of 0 to -6°C and lowered to -6 °C with lower slope. The highest content of proline was related to treatment at -6°C, which increased by 53% compared to control treatment. By decreasing the temperature, the survival rate decreased, so that the plants disappeared at temperatures below -9°C. Also, LT50el and LT50su occurred at temperatures of -10.153 and -8.958°C, respectively. Finally, the findings in this study showed that the medicinal plants withania can be tolerate at -6°C.