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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 'Fuji'/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.

For functional enhancement of apples, the effects of CuEDTA and FeEDTA foliar spray were investigated on the antioxidant contents and antioxidant activities in 'Hongro' fruit, which is a representative early season harvesting apple cultivar, at 30 days before harvest. The polyphenolic content of peel was significantly higher in the CuEDTA (1,228.6 mg/100 g) and FeEDTA (1,210.0 mg/100 g) spraying treatment groups compared to the control group (998.8 mg/100 g). The flavonoid content of peel showed the same trend as that of polyphenolic content. The ascorbic acid content of peel as also significantly increased in the CuEDTA and FeEDTA spraying treatment groups, but anthocyanin content was the highest in the control group (560.6 mg/100 g). The ABTS and DPPH radical scavenging activities were higher in the CuEDTA and FeEDTA spraying treatment groups than in the control group, but reducing power was not significantly different between the treatments. As a result of this study, 3% CuEDTA and FeEDTA spraying treatments at 30 days before harvest can be used to effectively enhance antioxidant contents in 'Hongro' apple.

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