Within-population variation in frost damage in Pinus contorta Dougl. seedlings after simulated autumn or late-winter conditions

Journal Article

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Single-tree progenies from a few populations of Pinus contorta were cultivated in a climate chamber and tested with respect to frost tolerance. The plants were exposed to -10C for three hours during the hardening period, simulating autumn conditions. Single-tree progenies and population samples were exposed to two, six, or twelve large diurnal temperature fluctuations, -10 to +20 C, simulating conditions inducing dehardening during late winter. Significant differences in frost damage were found between populations as well as between single-tree progenies from one of the populations after freezing during autumn conditions. The family repeatabilities for frost damage exceeded 0.50 in two of the three populations studied. Damage to plants increased with increasing number of simulated late-winter temperature fluctuations. This was the case both for the roots and the upper parts of the plants. No significant within-population variation in frost damange following exposure to simulated late-winter conditions as obtained. The simulating technique used is laborious and will not be further developed. There was a non-significant, postiive relationshiop between frost damange induced in single-tree progenies by simulated autumn and late-winter conditions.