Fruit and shoot growth, in relation to leaf vs. fruit ratio and their relative position in canopies of 'Flordastar' peach trees

The objective of this research was to study the effect on fruit growth of leaves vs. fruit relative location in scaffolds of Y shaped peach trees. Fruit growth and shoot extension growth were measured weekly on peach trees of the early maturing cultivar 'Flordastar' whose leaves and fruits were retained as follows: 1) trees with fruits and leaves throughout the two scaffolds; 2) trees with one scaffold with leaves and no fruits and one scaffold with fruits and no leaves; 3) trees with fruits and no leaves throughout the two scaffolds; 4) trees with one scaffold with fruits and leaves and one scaffold with fruits and no leaves. Fruits of all treatments showed the same growth during the first 3 weeks after bloom, then fruits in all the leafed scaffolds attained the largest size, while those on fully defoliated trees had the lowest. An intermediate fruit size was measured for fruits located in trees with no leaves in the fruiting scaffold and no fruits in the leafed one. Harvest size of fruits located in the scaffold with no leaves, of the treatment 4), was similar to that of fully defoliated trees. Final shoot length and thickness did not change with treatments, and the larger canopy development measured in branches with no fruits was related to a higher number of growing points rather than to their length. Results indicate that the close proximity between sources (leaves) and sinks (fruits) allows for maximum fruit growth, and that assimilate translocation between scaffolds is reduced by the presence of local sinks (fruit). The similar fruit growth achieved during the first 21 days after bloom in defoliated or leafed trees indicates that fruit growth in this period depends more on reserves than on new photoassimilates.