Dormancy, cold hardiness, dehardening, and rehardening in selected red raspberry cultivars

Abstract

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.