An Exothermic Process Involved in the Freezing Injury to Flower Buds of Several Prunus Species1

Abstract

Abstract Freezing injury to overwintering flower buds of apricot ( Prunus armeniaca L.), European plum ( P. domestica L.), Japanese plum ( P. salicina Lindl.), peach ( P. persica (L.) Batsch.), sweet cherry ( P. avium L.) and sour cherry ( P. cerasus L.) was found to be associated with an exothermic process detected on the time temperature profile. This exothermic process varied with seasonal fluctuations in the hardiness of 2 peach cultivars and was consistent with the hardiness of 5 cultivars tested on 3 dates during winter. No similar exotherm was detected in pear and apple. These results suggest that flower bud injury in some Prunus species was related to a specific event that involved freezing of a ‘bound’ or ‘supercooled’ fraction of water. This fraction of water remained unfrozen in the flower bud until the temperature fell below a critical level which in our studies was as low as -27°C. Exotherm flower bud hardiness in these fruit species.