Abstract
Pneumatic defoliation of apple trees is a novel approach to increase the penetration of sun radiation within the tree canopy to improve the formation of red color in the fruit peel, therefore improving the quality of bicolored apples. This work provides a deep investigation of the effects of summer pruning (SP), pneumatic defoliation (PD) and their combination (SP+PD) on the anthocyanin contents in the peel of ‘Nicoter’ and ‘Rosy Glow’ apples with particular attention to the fruit side (sun-exposed, sun-averted) and its location on the tree (inside or outside the canopy, west or east side of the tree). Apple peels of ‘Rosy Glow’ enhanced their anthocyanin levels by 61, 81, and 85% following SP, PD, and SP+PD, respectively, independent of the fruit side and orientation. The efficiency of the treatments in ‘Nicoter’ significantly depended on the position of the apple within the tree canopy and on the side of the fruit: inside the canopy, treatments increased the anthocyanin content of the sun-exposed fruit side by 39, 128, and 144% following SP, PD, and SP+PD, respectively. On the outer side of the tree canopy, only PD or SP+PD enhanced the anthocyanin contents on the sun-averted side of ‘Nicoter’ fruit (by 44 and 76%, respectively), while none of the treatments proved to be significantly efficient on the sun-exposed side of apples grown on the outer side of the canopy. The observations from our study constitute the basis for the routine employment of the novel pneumatic defoliation technique in the commercial cultivation of bicolored apple cultivars.