Magnetic resonance imaging (MRI) as a method for determination of freezing injury in strawberry crowns

In an experiment with controlled freezing, strawberry plants were exposed to 0, −8, −12, −16 and −20°C at a freeze and thaw rate of 2 °C/hour in March/April 1996. Crowns from the cultivar ‘Korona’ were examined using magnetic resonance imaging (MRI), showing a gradual increase of signal intensity from the centre of the crowns, as a result of the temperature drop, which might be caused by lipids. The increase in signal intensity was in accordance with the tissue browning of crowns, which increased substantially when the temperature dropped below −12 °C. A similar reaction was shown in a field experiment comparing wintercovered and not wintercovered strawberry plants. The plants which had been exposed to temperatures between −10 and −16 °C were severely injured. This demonstrates that MRI has a potential as an objective method to determine freeze injury in the field, by «calibrating» the MRI instrument to freezing profiles in controlled experiments.