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

Acclimation and deacclimation of primary bud cold hardiness in `Norton', `V ignoles', and `St. Vincent' grapevines were studied at Southwest Missouri S tate University Research Campus in Mountain Grove, Missouri, USA. Canes fro m mature vines were acclimated at -10 degreesC for 7 d and then subjected t o deacclimation at 20 degreesC for 1, 2, 3, 5 and 7 d in January and Februa ry 1997. During 1997-98 winter season, they were acclimated at -7 degreesC and deacclimated at 20 degreesC for 1, 2, 3, 5, and 7 din December, Februar y, and March. Cold hardiness of primary buds under field temperature condit ions was also evaluated at the same time as the buds treated under laborato ry 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 lea st cold hardy cultivar, while `Vignoles' was least sensitive to acclimating and deacclimating temperatures. Cold hardiness of primary buds decreased g radually while their sensitivity to acclimating and deacclimating temperatu res increased, from December to March. Exposure to -7 or -10 degreesC incre ased cold hardiness and exposure to 20 degreesC decreased cold hardiness du ring certain sampling periods but not always so. It seems that there is a m aximum level of cold hardiness above which primary buds will not acclimate and there is a minimum level of cold hardiness below which primary buds wil l not deacclimate.