Three experiments were conducted to determine the deacclimation potential of cultivar 'Seyval blanc' (Vitis × sp.) grape tissue. In the first experiment, tests were conducted to determine the relationship between dormancy and hardiness of 'Seyval blanc' bud and cane tissue collected from 25 November 1986 to 16 March 1987. On 15 December, 11 January, 22 February and 16 March the numbers of days to budbreak were 44, 37, 30 and 7 days, respectively. By December, the temperature at which 50% of the primary buds were injured (T50) declined to a minimum near -23°C. Similarly, phloem acquired a maximum hardiness by December with 50% browning injury occurring at -27°C. Xylem exhibited only minor injury at -30°C in December. All tissues deacclimated greatly between 15 February and 16 March. In the second experiment, grape tissue was collected on 18 January and 22 February 1987 to determine the susceptibility of buds, phloem and xylem to freezing injury after exposure to 16°C for 0, 12, 24 and 48 h. Tissues deacclimated linearly with time at 16°C at both sampling dates. However, stem tissues deacclimated at a faster rate in February than in January. In the third experiment, grape canes were subjected to one or two episodes at 16°C for 4 h before cooling to temperatures in the range of -15 to -33°C on 11 January and 15 February. In January, primary buds and phloem exposed to two episodes with a minimum temperature of -5°C between episodes were generally hardier than those tissues subjected to warming episodes which were not followed by -5°C. At both sampling dates, the primary buds, phloem and xylem exposed to two episodes did not deacclimate more than tissues subjected to one episode. © 1991.
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