Evidence for non-occurrence of node-to-node or stem-to-bud transfer of chilling temperature signal for dormancy release

In the current context of global changes, phenology is expected to be one of the major processes affected by temperature increase, notably through the dynamics of endodormancy release. However, the actual impact on bud break pattern is difficult to predict due to poor knowledge about the spatial extent of chilling sensing, which likely affects bud break heterogeneity. Indeed, contrary to a widely held opinion, the strictly local perception of the chilling air signal has never been demonstrated. The present experiment addresses this issue through local chilling or heating of selected nodal groups of buds on shoots of peach tree under endodormancy. A temperature-conditioned localizable air-jet device was designed to provide the sharpest possible temperature contrast between selected treated buds and the 'not-treated' rest of the tree structure, including adjacent axis tissue. Different chilling doses were tested over two experimental seasons, and a heat treatment was applied on single nodes in a cold environment. Chilled vegetative buds did not break when the local chilling dose received was less than 50% of the requirements even though neighboring axis tissue received the standard chilling dose. The maximum rate of bud break reached 80% at chilling completion and most of the broken buds produced long shoots. We conclude that temperature sensing occurs on a very local scale with the signal not reaching neighboring untreated buds, meaning that endodormancy release should be considered a very local process. The local response permits analysis of the intra-canopy heterogeneity of bud break and the possible relationship between bud status and intra-canopy heterogeneity of bud temperature.