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  • Author or Editor: Annette M. Zatylny x
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Two selections and two cultivars of red raspberry (Rubus idaeus L.) were evaluated for cold hardiness in vitro. Tissue-cultured shoots were exposed to temperatures from 0 to –18C and samples were removed at 2C intervals. Injury was assessed by a visual rating of tissue browning after freezing. Only shoots subjected to step-wise acclimation at low temperatures before freezing revealed significant differences among the four types in the lowest shoot survival temperature. Acclimation treatments increased the lowest survival temperatures of in vitro shoots by a mean of 3.1C. The hardiness obtained from this screening method agreed with that of winter survival in the field. Ranking, from the most to least cold hardy, was `Boyne', Gu 72, Gu 63, and `Comox'.

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Tissue survival assessments of red raspberry (Rubus idaeus L.), including cane dieback, bud death, time of cane leaf drop, and growth cessation, were compared to freezing tests of stem portions and buds. Four named cultivars and six Guelph (designated Gu) selections were assessed in the field at two locations in each of two winters and in concurrent controlled freezing tests at one location for one winter. The time of cane leaf drop and of cessation of cane extension growth in the fall were not correlated with field survival. Cane dieback as a percentage of cane length was a better estimate of winter survival than was bud number. Controlled freezing tests of stem portions and buds, and calculation of T40s and T50s indicate that genotypes differed in their relative hardiness throughout the winter. The different methods of field assessment of cold hardiness were well correlated, but not well correlated with controlled freezing tests (4.2% significant correlations). Exclusion of the genotype, Gu 75, which behaved differently in the field than in freezing tests, increased the number of significant correlations to 16.7%.

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