Pre-Harvest Pneumatic Defoliation and Pruning Improves Peel Coloration of ‘Nicoter’ and ‘Rosy Glow’ Apples Depending on Exposition, Fruit Side and Weather Conditions

Peel coloration in bicolored apples is decisive for their commercial value and varieties like ‘Nicoter’ and ‘Rosy Glow’ need to achieve 33 and 40% red peel color to be marketed under the trade names ‘Kanzi®’ and ‘Pink Lady®’, respectively. Pneumatic defoliation of apple trees is a novel technique to lower the amount of leaf area and, along with pre-harvest pruning, it can improve peel coloration by increasing sunlight incidence on fruit. Our experiments showed that in fact the color index and the amount of anthocyanins, the latter being responsible for the red fruit peel, increased up to 100% after pneumatic defoliation (PD) and pre-harvest pruning (P), or their combination (P+PD), over three years. Anthocyanin contents in ‘Rosy Glow’ apple peels rose irrespective of the orientation and side of the fruit, while in ‘Nicoter’ they increased only on the sun-exposed fruit side. The extent depended on the harvest year and its meteorological conditions and our results showed that the effect is greater in years with high pre-harvest temperatures. In most combinations of year and variety, the three treatments P, PD and P+PD were equally effective.