SCREENING RED RASPBERRY FOR COLD-HARDINESS IN-VITRO

Two selections and two cultivars of red raspberry (Rubus idaeus L.) we re 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 a fter freezing. Only shoots subjected to step-wise acclimation at low t emperatures before freezing revealed significant differences among the four types in the lowest shoot survival temperature. Acclimation trea tments increased the lowest survival temperatures of in vitro shoots b y a mean of 3.1C. The hardiness obtained from this screening method ag reed with that of winter survival in the field. Ranking, from the most to least cold hardy, was 'Boyne', Gu 72, Gu 63, and 'Comox'.