Identification and Timing of Dormant and Ontogenetic Phase for Sweet Cherries in Northeast Germany for Modelling Purposes

Some important stages of plant development, such as dormancy release and beginning of ontogenetic development, cannot be easily observed so that semi-mechanistic phenological models of spring phases mostly does not accurately reflect the control of these physiological stages. For this reason, over 6 years we studied weekly changes of Fresh Weight (FW), Dry Weight (DW), Water (WC), Nitrogen (NC) and Carbon Content (CC) in sweet cherry buds (Prunus avium L., cultivar ‘Summit’), from October to mid of April (stage ‘open cluster’, BBCH 56). Together with an experimental study to determine the date of endodormancy release, we were able to define the annual variability and average duration in the timing of para- endo-, and ecodormancy phase for sweet cherries, cultivar ‘Summit’. The secession of growth in autumn starts when all leafs has fallen down (BBCH 97) and marks the transition from para-to endodormancy. During endodormancy all investigated parameters reached a constant level which also did not change during ecodormancy. Our results showed that ecodormancy can be a relatively long phase in temperate climates, which must be adequately handled in phenological models. Beginning of ontogenetic development was clearly related to steadily rising water contents in cherry buds, which stayed stable during endo- and ecodormancy. Thus, this study highlights the importance of bud’s water content to define dormancy phases as well as beginning of ontogenetic development. The latter one was induced by continuously rising air temperatures above the freezing point. Physiologically, beginning of ontogenetic development is a flexible date which occurred on average 26 days before bud swelling was observed.