Transport and partitioning of 13C-photoassimilate between peach fruiting shoots

We used a non-intrusive method (13CO2 feeding) and a manipulative approach to see whether fruiting shoots in peach trees are autonomous or may import carbon from neighboring shoots under forced conditions, and whether the degree of autonomy is influenced by the source-sink relationship on the shoot. In three experiments, leaf to fruit ratio (L:F) of selected fruiting shoots was moderately (2005 and 2006) or strongly (extreme enforcing 2006) altered to either encourage or discourage movement of carbon from 13C-labeled sending shoots (SFS) to receiving fruiting shoots (RFS), both located on the same main scaffold of V-shaped peach trees. At stage I and III of fruit growth, fruit and shoot tips were sampled from SFS and RFS for determination of 13C percentage on the same day of labeling and after 1 week. In all three experiments and both growth stages, most of the 13C was found in fruits and shoot tips of SFS and nearly none translocated to RFS. At stage III of 'Redhaven' peach fruit growth (2005), some 13C was also detected in fruits of RFS only in the Encourage treatment and on the same day of labeling. In the extreme enforcing experiment, when all sinks were removed only from SFS, a small but detectable amount of 13C was also recovered only in fruits of RFS at both growth stages. The results obtained in this study indicate a relatively high degree of peach branch autonomy even at the fruiting shoot level. However, conditions of strong imbalance between source supply and sink demand, either experimentally imposed or during periods of strong vegetative and reproductive sink competition, may cause some movement of carbon across neighboring fruiting shoots.