Deep Supercooling of Dormant and Deacclimating<i>Vitis</i>Buds

Abstract

Differential thermal analysis was used to measure deep supercooling in dormant buds of 15 <i>Vitis vinifera</i> L. cultivars, <i>V. labruscana</i> Bailey cv. Concord and four <i>Vitis</i> hybrids. The primary, secondary and tertiary buds in each compound bud produced discrete low temperature exotherms (LTE9s). In singlebud experiments with White Riesling the largest LTE9s originated from the primary buds. The temperature of the median low temperature exotherm (LTE₅₀) increased about 11°C in White Riesling from late winter to early spring but increased 14°C in Concord and over 16°C in the French hybrid Chelois over the same period. These LTE₅₀ increases are consistent with the characteristic deacclimation patterns of White Riesling and Concord buds. The LTE₅₀ of White Riesling bud samples in late winter was within 1°C of the temperature which killed 50% of the buds under programmed freezing.