COLD-HARDINESS IN RUBUS

More than 80 raspberry and 42 blackberry genotypes were evaluated for cold hardiness after controlled laboratory freezing in January 1990. R ed, yellow, black, and purple raspberry cultivars (R. idaeus L., R. ne glectus Peck), blackberry cultivars (R. allegheniensis Porter, R. ursi nus Cham and Schldl.) and other Rubus species selections were examined . T-50's, the temperatures where 50% of the samples were killed, were calculated for cane (cambial region), bud and bud base of each genotyp e. Red, purple, and black raspberries had a lower T-50 values than did blackberries. The T-50 value of Rubus idaeus L. cv. Burnetholm canes was -34C. Hardy summer bearing red raspberries, 'Canby' and 'Puyallup' had a T-50 value of -30C; 'Canby' buds -26C; Puyallup -20C. The T-50 values of fall fruiting red raspberries such as 'Zeva Remontante: Indi an Summer', 'St. Regis', and 'Fallred', ranged from -23 to -25C. Sever al purple raspberries (Rubus neglectus Peck cvs. Brandywine, Royalty) were suite cane hardy, with T-50 values lower than -33C. The buds and bud bases of these purple raspberries, however, had T-50 values at mos t -25C. Canes of several black raspberries (R. occidentalis L. cvs. Ne w Logan, Bristol) had T-50 values of -28C; buds -27C and -17C, respect ively. 'Bristol' offspring had To values as much as 15C less than the parent. Canes of the hardiest blackberry cultivar, (R. sp. cv. Black S atin) had a T-50 value of -23C; buds were -19C. In many raspberry and some species genotypes examined, the region of the bud at the axis at the cane was less hardy than were tissues within the bud scales. The T -50 values of canes of most cultivars ranged from about 2 to 15 degree s hardier than buds.