Hardening and dehardening of peach flower buds

Abstract

At the northern borders of the peach-growing zone, low temperatures during winter are the critical factors for the survival of the trees and for the reliability of production. Our aim was to carry out detailed analysis of the hardening and dehardening processes of flower buds of three peach cultivars with contrasting frost tolerance and to evaluate the effects of environmental factors and of genotypic differences in two consecutive winters with very diverse weather conditions. Based on our results, the hardening process takes place in two phases in peach flower buds. In the first phase, gradual cooling is essential if the level of frost resistance characteristic of the genotype is to develop, but in the second phase, it is a prerequisite that the external temperature drop consistently below zero for reaching the maximum frost tolerance. The maximum level of frost resistance developed by peach flower buds was only maintained for a limited time and the differences between the cultivars gradually decreased as flowering time approached. At the time of leaf fall in the fall and before flowering, the difference between the mean frost tolerance values for flower buds of the extremely frost-tolerant and frost-sensitive cultivars was only 2 °C, whereas in midwinter, it was 5 to 5.5 °C.