Freezing survival and supercooling in primary and secondary buds of Rubus spp

Primary and secondary buds from 11 blackberry (Rubus subgen. Rubus) and 10 red raspberry (Rubus idaeus) cultivars were subjected to viability testing to determine their relative hardiness from November 1987 through March 1988. Of the blackberries tested, Darrow floral buds were found to be the most hardy throughout dormancy. Forty-five percent of primordia in Darrow primary buds survived −33 °C in January. Most blackberries had reproductive secondary buds that generally survived lower temperatures than the primary buds. Of the red raspberries tested, Canby and Chilliwack had good primary bud hardiness in January and March. Primary buds of red raspberries were usually injured at warmer temperatures than secondary buds. Differential thermal analysis experiments were conducted on primary and secondary buds of Dirksen and Shawnee blackberry and Nordic and Reveille red raspberry at each test date to determine their freezing characteristics. The low temperature exotherms detected in primary buds of each cultivar were correlated with freezing injury, but their number seldom corresponded to the number of differentiated floral primordia. Low temperature exotherms were also detected in some of secondary buds of Dirksen and Reveille which contained differentiated floral primordia.Key words: Blackberries, raspberries, cold hardiness, differential thermal