Seasonal changes of physiological parameters in sweet cherry (Prunus avium L.) buds

• Studies concerning chilling requirements of sweet cherry are of great importance to improve phenological models.
• Mainly the release of dormancy is still a black box in phenological modelling.
• We investigated changes in sweet cherry buds of ‘Summit’ with respect to different physiological parameter in 2011/2012 and 2012/2013.
• Our results suggest that ABA and the ABA-isomer in the sweet cherry buds regulate differentiated metabolic processes in the dormant stage and during bud growth and development.

Studies concerning chilling requirements of sweet cherry are of great importance to improve phenological models on the base of plant physiological processes. Mainly the release of dormancy is still a black box in phenological modelling. From an economical point of view, sweet cherries are one of the most interesting fruits, but information about the relationship between dormancy, growth and development of flower buds under the climatic conditions of the North Eastern Germany are scarce. The presented 2 year results are to our knowledge the first under natural conditions in fruit tree orchards with a high temporal resolution during the dormant stage (October) until cluster development (April). We investigated changes in sweet cherry buds of ‘Summit’ with respect to fresh and dry weight, water content, C- and N/15N content, abscisic acid (ABA), an ABA-isomer, sugars, carotenoids, and free amino acids (asparagine, aspartic acid, isoleucine) in 2011/2012 and 2012/2013.The transition from dormant stage to the beginning of growth was first obvious by markedly changes of the water content. The phase from green tip to tight cluster, with a length of only 4 days, was the period of the most physiological activity in single buds, because of the highest daily accumulation rates of fresh/dry weight, C, N. We assume a concentration dependant regulation of the member of the aspartate family (asparagine, aspartic acid, isoleucine) during dormancy, growth and development in sweet cherry buds. The ABA content showed 2011/12 a clear bimodal pattern which was at lower level similar in 2012/13, but not so strong incisive. In both years, the first peak was probably related to the end of endodormancy. However the ABA-isomer content showed in both seasons a unimodal pattern. The maximum of the ratio of ABA-isomer/ABA indicated the beginning of ontogenetic development which starts 3 and 2 weeks later, respectively. Our results suggest that ABA and the ABA-isomer in the sweet cherry buds regulate differentiated metabolic processes in the dormant stage and during bud growth and development. After replication in the season 2013/14 the estimated dates of release of endodormancy, beginning of ecodormancy and start of ontogenetic development will be used to validate and improve phenological models for the beginning of cherry blossom.