CONTROLLED FREEZING AS THE COLD TEMPERATURE TOLERANCE TEST FOR STRAWBERRY CULTIVARS

During the winters between 2009-2011 frost resistance of artificially frozen plants of seven strawberry cultivars originating from different locations was examined. The tested cultivars were ‘Ventana’ (from California), ‘Elsanta’ (from The Netherlands) and ‘Elkat’, ‘Filut’, ‘Salut’, ‘Selvik’, and ‘Vikat’ – all Polish bred cultivars. Freezing of plants was performed in a Freezing Chamber BINDER GmbH, Germany. The test was conducted on cold stored plants (category A+), which were individually planted into the pots directly before freezing. Plants were subjected to different temperatures for a period of 3 h: -5, -8, -10, -12 and -15°C. During freezing the temperature was lowered at the rate of 1°C per hour and after freezing it was raised at the same rate until reaching the level of -2°C. Immediately after freezing the plants in pots were placed in the cold store where they stayed until the beginning of April when they were transferred outside (open field conditions). Six weeks later plant growth vigor was evaluated. The most pronounced differences between cultivars regarding the plant vigor were observed on plants frozen at -10°C. It was evident that plants of the Polish strawberry cultivars were more tolerant to the low temperature stress than cultivars originating from warmer climatic regions like ‘Elsanta’ and ‘Ventana’. The controlled freezing can be regarded as the efficient cold temperature tolerance test for strawberry cultivars originating from different regions.