Summer pruning and reflective film enhance fruit quality in excessively tall spindle apple trees

Abstract

Tall spindle planting systems achieve high-quality fruit from plants that flower early and sustain a high yield. While some growers in Korea let apple trees grow up to 4 m or higher in high-density planting systems with M.9 rootstock to produce more fruits, such practices lead to very tall trees with low-quality fruit that develop in the lower canopy. To minimize this effect, we used the ‘Hongro’ cultivar to examine the effect summer pruning and installation of reflective film had on fruit size and quality in the lower canopy. We measured light distribution, diameter of flower buds, fruit quality, and leaf physiological characteristics at different parts of the canopy of trees that were treated with summer pruning (SP) and the installation of reflective film (RF), compared to those allowed to maintain their dense canopies (unpruned control; UC). The SP + RF treatment improved the overall light availability throughout the canopy and increased the amount of light by approximately 25% in the lower parts of the canopy compared to that in the UC group. The SP + RF treatment increased size, color, and soluble solids content in fruits from the lower parts of the canopy. Moreover, this treatment increased leaf photosynthetic activity, specific leaf weight, and flower bud diameter. Therefore, summer pruning and the installation of reflective film helps light penetration in excessively tall spindle trees and improves fruit quality in a high-density apple production system.