Flower Bud Cold Hardiness of 'Muskoka' Red Raspberry as Related to Water Content in Late Winter

'Muskoka' red raspberry (Rubus idaeus L.) canes were sampled from a field (latitude 60 degrees 10'N) at 2-to 3-week intervals from February to April to examine whether the loss of cold hardening capacity in late winter is connected to the increase in bud water content, or to the increased ability of buds to absorb water. Bud base vascular tissue lost its hardening capacity earlier than floral primordia and was injured at warmer temperatures. Cold hardiness was more closely correlated with bud water content than with water potential. Both low water content and low water potential indicated the ability of tissue to harden at low temperatures. All determined parameters except hardening capacity were positively correlated with mean air temperature during a 2-day period preceding sampling. Loss of bud base vascular tissue hardening capacity coincided with increases in bud water content, maximal water content and water potential in the beginning of April, after diurnal mean temperature had risen above 0 degrees C. (C) 2006 by The Haworth Press, Inc. All rights reserved.