Branch removal and defruiting for the amelioration of water stress effects on fruit growth during Stage III of peach fruit development

The removal of half the canopy in peach trees was studied to understand the limits and possibilities of using summer pruning as a drought management strategy for fruit production. Pruning involved removal of entire branch-scaffold units. Since large branches are regarded as almost totally autonomous for carbon during Stage III of fruit growth, any benefit in fruit growth from canopy removal should be related to an increase in tree water status. Four different combinations of irrigation and bearing treatments were applied: (1) C-FI, full irrigation treatment applied only to trees with fruit distributed evenly, (2) C-DI, deficit irrigation during Stage III (irrigated at 50% of C-FI) applied to trees with fruit distributed evenly, (3) SDef-DI, deficit irrigation during Stage III (irrigated at 50% of C-FI) applied to trees with half of the scaffolds defruited, and (4) SRe-DI, deficit irrigation during Stage III (irrigated at 50% of C-FI) applied to trees with half of the scaffolds entirely removed. Three different thinning intensities were applied subsequently to all treatments (non-thinned, commercially thinned and heavily thinned) in order to provide an expression of the treatment effects across varying fruit load levels. Stem water potential (Ψstem) was measured with a pressure chamber at solar noon, and fruit growth was estimated from fruit samples at the onset of Stage III and the total fruit picked at harvest. C-FI trees had Ψstem values around −0.8 MPa, whereas C-DI trees during the whole Stage III had an average Ψstem of −1.36 MPa, while the different bearing patterns resulted in significant changes in Ψstem. Ψstem was increased in the SRe-DI treatment by an average of 0.25 MPa compared to C-DI. Ψstem was increased in the SDef-DI treatment by an average of 0.2 MPa compared to C-DI. Fruit relative dry matter was linearly related to Ψstem whereas fruit growth in dry matter was only reduced for treatments having average Ψstem values lower than −1.2 MPa. Accordingly, the improvement in water status achieved by SRe-DI and SDef-DI treatments could be related to the maintenance of fruit growth in dry matter. From a fruit carbon standpoint, defruiting half of the trees was almost as effective as a drought management strategy as was removing half of the scaffolds by pruning.