Effects of Temperature on the Deep Supercooling Characteristics of Dormant and Deacclimating Sweet Cherry Flower Buds

Abstract

Seasonal changes in the temperature of the median low-temperature exotherm (LTE 50 ) of dormant sweet cherry ( Prunus avium L. cv. Bing) flower buds were significantly correlated with the preceding minimum air temperature in the orchard and the water content of the flower primordia. When buds were exposed to temperatures just below the high temperature exotherms, water migrated from the primordia to the bud scales. Under these conditions, the LTE 50 decreased almost 5°C during the first day, but only 1°/day thereafter. The minimum LTE 50 was near −32° after the buds were frozen for 10 days. Thawing buds at 0° or above increased the LTE 50 about 1°/hr, to −20° to −21°. The LTE 50 did not increase above these temperatures until the buds were exposed to 20° for 1-2 days following the completion of rest. During deacclimation, both the LTE 50 and temperature range of the low temperature exotherms (LTEs) increased. These changes were accompanied by fluctuations in the capacity of the flower buds to exhibit deep supercooling, expressed as the fraction of an LTE produced per flower primordium (LTE/primordium). Even on days when the LTE/primordium was low, the temperature required to injure 50% of the flower primordia was similar to the LTE 50 .