Acclimation and deacclimation of primary bud cold hardiness in ‘Norton’, ‘Vignoles’ and ‘St. Vincent’ grapevines

Summary Acclimation and deacclimation of primary bud cold hardiness in ‘Norton’, ‘Vignoles’, and ‘St. Vincent’ grapevines were studied at Southwest Missouri State University Research Campus in Mountain Grove, Missouri, USA. Canes from mature vines were acclimated at -10°C for 7 d and then subjected to deacclimation at 20°C for 1,2,3,5 and 7 d in January and February 1997.During 1997-98 winter season, they were acclimated at -7°C and deacclimated at 20°C for 1, 2, 3, 5, and 7 d in December, February, and March. Cold hardiness of primary buds under field temperature conditions was also evaluated at the same time as the buds treated under laboratory conditions. Cold hardiness of primary buds was influenced by temperature regimes, and the length of exposure time to acclimating and deacclimating temperatures. ‘Norton’ was the most cold hardy and ‘St Vincent’ was the least cold hardy cultivar, while ‘Vignoles’ was least sensitive to acclimating and deacclimating temperatures. Cold hardiness of primary buds decreased gradually while their sensitivity to acclimating and deacclimating temperatures increased, from December to March. Exposure to -7 or -10°C increased cold hardiness and exposure to 20°C decreased cold hardiness during certain sampling periods but not always so. It seems that there is a maximum level of cold hardiness above which primary buds will not acclimate and there is a minimum level of cold hardiness below which primary buds will not deacclimate.