The effects of three levels of irrigation water on the improvement of cold tolerance of acclimated viola

Due to global climate changes, the growth of ornamental plants will be influenced by warming episodes in winter. The purpose of this examination was to estimate the effect of three levels of irrigation regimes on the freezing tolerance of acclimated viola ( Viola × wittrockiana ‘Iona Gold with Blotch’). This experiments included three irrigation regimes (80, 60 and 40% FC) with different temperatures (20, 0, − 3, − 6, − 9, − 12, − 15, − 18, − 21 and − 24 °C). After irrigation regimes, proline and carbohydrate contents were recorded. Then, plants were moved to the thermo-gradient freezer and electrolyte leakage percentage (EL %), survival percentage (SU %), lethal temperature resulting in 50% mortality according to the electrolyte leakage percentage and survival percentage (LT50el and LT50su) were evaluated. The carbohydrate and proline content increased when plants were under drought stress conditions. Electrolyte leakage percentage across three levels of irrigation treatment increased by lowering the temperature; this increase at − 24 °C was fivefold more than the control. Survival percentage in all treatments was not affected in the thermal ranges of 0 to − 9 °C, but decreasing the temperature to − 24 °C resulted in the full loss in all treatments. Vegetative growth and reproductive components were significantly affected by drought and freezing temperature treatments. Dry weights of different parts of plants reached peak values when plants were under 60% FC at 0 °C condition. A negative correlation between LT50el with carbohydrate and proline levels was found and drought treatment significantly increased freezing tolerance (lower LT 50 ) in plants grown under 60% FC compared to other treatments.