ADAPTATION TO COLD TEMPERATURE AND RESPONSE TO FREEZING IN WALNUT TREE

In south-central France, Walnut exhibited freezing tolerance by acclimation in the fall and deacclimation in the spring. This involved a sequence of active processes that result in well-defined changes in cellular composition (starch level in particular). At the same time, the response to freezing by dehydration of cells showed that Walnut trees present also freezing avoidance. We developed a new simple tool for testing cold hardiness and compared it with the classical LT50 test (electrical leakage conductivity). The new test gave similar results. We observed also similar results for both tests when applied to cold-deprived trees (in greenhouse >15°C). Frost hardiness was correlated with carbohydrate reserve status in the both cases (cold-deprived trees and orchard trees).