Influence of branch autonomy on fruit growth and quality in nectarine trees

Different studies have reported that peach tree branches are characterized by partial autonomy for carbon budget. Most of the studies have focused their attention on fruit growth, whereas no information is available about the effect of branch autonomy on fruit composition. The aim of this experiment was to study how branch autonomy affects fruit size and quality in nectarine trees. The trial was conducted in 2008, in Eboli (Italy), on ‘Rose Diamond’ nectarine trees grafted on GF677. The experiment compared four thinning treatments: a control treatment (C) including trees that were commercially fruit-thinned; a flower-bud thinning treatment (BT) applied homogeneously in all the canopy; a bud-thinning treatment where all the flower-buds of the top half of the canopy were removed, whereas in the bottom canopy layer thinning was applied at fruit stage as in the C treatment (Top-BT); the fourth treatment was similar to Top-BT, with the differences that the bottom layer was completely flower-bud thinned and the top commercially fruit thinned (Bottom-BT). Crop load in each canopy layer was very similar between treatments. BT treatment induced significant increments in fruit fresh weight at harvest in both canopy layers and in soluble solids content (SSC) only in the bottom layer compared to the C. Interestingly, fruit size (in both canopy layers) and SSC (only in the bottom canopy layer) was higher in Bottom-BT and Top-BT trees compared to BT trees. The a* coordinate of the fruit skin cover color decreased slightly in thinned trees compared to control. Skin ground color and flesh firmness were very similar in Bottom-BT, Top-BT, and C trees. These results suggest that branch autonomy is only partial and carbon can move along relatively short pathways from canopy layers where demand for carbon is lower to layers where the demand is higher. These effects depended on the measured parameters and the canopy layer.