The above photos depict freezing damage inflicted upon needle, bud and stem tissue, showing moderate to severe damage.
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Artificial freeze testing involves collecting branch tips from test population and subjecting them to freezing temperatures. Several samples from each tree are taken so that multiple temperatures can be tested in replicate. The labeled branch tips are kept in ice coolers during transport and stored in 2o C walk-in coldboxes while they are prepared for treatment. Samples are wrapped in damp cheesecloth and aluminum foil and stored overnight at -2o C. The temperature was lowered 3-5o C per hour until the selected test temperature was attained. The samples were treated with the test temperature for one hour and then stored at 2o C 24 hours so that the samples thaw slowly. After equilibrating at 2o C, the samples are stored at room temperature for 1 week and then scored for freezing damage.
Preliminary tests are conducted 1-2 weeks prior to experiment to determine the optimum test temperatures that will reveal the greatest variation in the test population.
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| references: |
Aitken SN and Adams WT (1996) Genetics of fall and winter cold hardiness of coastal Douglas-fir. Can J For Res 26:1828-1837.
Aitken S. and Adams WT (1997) Spring cold hardiness under strong genetic control in Oregon populations of coastal Douglas-fir. Can. J. For. Res. 27(11): 1773-1780.
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