Effect of temperature preconditioning on ovary freezing tolerance of fully opened peach flowers

Abstract

One year old peach trees, chilled for eight to ten weeks at 5°C, were placed in a cold (15°C day, 5°C night) or warm (30°C day, 20°C night) growth chamber prior to bud break to study the influence of long-term low temperature preconditioning on freezing tolerance of flower ovaries. The trees bloomed after four weeks in the cold chamber and two weeks in the warm chamber. Ovary freezing tolerances were determined by either freezing whole flowering trees or detached flowers. When whole trees were frozen, ovaries of cold- grown ‘Junegold’ survived a freezing temperature of -4.0°C, but were killed at -4.5CC. Also, ovaries of cold-grown ‘Junegold’ were hardier than those of warm-grown trees, with differences in ovary freezing survival ranging from 13% at -4.0°C to 35% at -3.0°C. However, the difference in T50 of the ovaries between the warm-grown and the cold-grown flowers was only 0.38°C. Moreover, the cold acclimation potential for ovaries of ‘Junegold’ peach was lower than that of leaves and stems by at least 3°C. Under detached flower freezing, ovaries of cold-grown ‘Loring’ were hardier than those of warm-grown ones, with difference of 23.3% at -2.5°C. However, no differences between the cold- and warm-grown ‘Redhaven’ ovaries were found.