Dormancy, Cold Hardiness, Dehardening, and Rehardening in Selected Red Raspberry Cultivars

in Journal of the American Society for Horticultural Science
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  • 1 Department of Plant Production, P.O.Box 27, FIN-00014 University of Helsinki, Finland

Canes and flower buds of selected red raspberry cultivars (Rubus idaeus L. `Maurin Makea', `Muskoka', and `Ottawa') were sampled from a field (latitude, 61 °20'N; longitude, 24 °13'E) at 1-month intervals during Winter 1996-97 to study the interaction of dormancy and cold hardiness, hardiness retention, and rehardening capacity. One set of canes was subjected to dehardening (3 days) and two sets to dehardening + rehardening (3 and 7 days) treatments before cold hardiness determination. Maximum midwinter hardiness occurred in January, after breaking of endodormancy. Cold hardiness of canes and buds reached -28.6 to -37.2 °C and -24.2 to -31.6 °C, respectively. Throughout the winter, raspberry canes were hardier than buds. Endodormancy had a greater influence on dehardening and rehardening in buds than in canes, and cultivars differed in their response. Dehardening of `Maurin Makea' canes and buds, and `Muskoka' buds was slightly enhanced by breaking of dormancy, whereas dehardening in `Ottawa' was not affected by dormancy. Raspberry canes and buds could reharden even after dormancy release. Rehardening capacity was affected by the state of dormancy only in `Maurin Makea' buds. Changes in dormancy status failed to explain cultivar differences regarding dehardening and the capacity to reharden suggesting other factors may be involved.

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