Defoliation and Fruit Coloration in 'Fuji'/M.9 Apple Affected by Cu-EDTA and Fe-EDTA Foliar Spray

Abstract

The objective of this study was to determine whether two chelate compounds (Cu-EDTA and Fe-EDTA) applied as a foliar spray could effectively defoliate 'Fuji '/M.9 apple trees and improve fruit quality and fruit coloration. Foliar spray with these two chelate compounds at 30 days before harvest significantly defoliated fruit cluster leaves, which improved light interception of Tuji'/M.9 apple trees. However, Cu-EDTA non-selectively defoliated bourse shoot leaves and true leaves, which are involved in photosynthesis during the late period of fruit growth. Cu-EDTA markedly reduced fruit weight, soluble solids content, and fruit coloration compared to Fe-EDTA. Regarding Fe-EDTA concentration, 3% Fe-EDTA was more effective at enhancing fruit coloration but lowered fruit weight compared to 1% Fe-EDTA. Consequently, we found that 1% Fe-EDTA induced more selective defoliation of fruit cluster leaves than Cu-EDTA and was more effective in improving fruit quality and fruit coloration of 'Fuji' apple trees.