Prediction of cold hardiness in Douglas fir seedlings by index of injury and conductivity methods

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Abstract
Electrical conductivities of diffusate from stem segments of Douglas fir (Pseudotsugamenziesii (Mirb.) Franco) were measured after exposing segments to various freezing temperatures and after heat killing. These data were expressed as conductivity percentage (conductivity after freezing as a percentage of conductivity after heat killing) or as index of injury (It, equivalent to conductivity percentage corrected for conductivity of unfrozen sample). Conductivity percentage, meaned over six test temperatures, predicted the temperature lethal to subsamples of whole plants exposed to different freezing temperatures reasonably well (R2 = 0.77, SEE = ±3.3 °C). However, 'critical' values of It associated with the temperature lethal to 50% of whole plants (T50) could only be determined for the three lowest test temperatures, and they varied from 32 to 40. In a controlled-environment experiment, levels of hardiness predicted by mean conductivity percentage, which seemed the most promising method, did not fully agree with survival results obtained from whole plants after freezing tests.

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