Hand leaf thinning for improvement of fruit coloration and quality is one of the most labor-consuming works in Korean apple cultivation. The study was aimed at investigating whether foliar application of two chelate compounds (Cu-EDTA, Fe-EDTA) could defoliate effectively ‘Hongro’/M.9 apple leaves and enhance fruit coloration and quality. At 30 days before harvest, foliar spray with two chelate compounds defoliated significantly the apple leaves. Chelate treatments did not affect the leaf chlorophyll content. High concentration of chelates decreased drastically photosynthetic rate of true leaves, and then it stayed in low levels, whereas low levels of chelates reduced sharply the photosynthetic rate but it was gradually restored over time. Cu-EDTA regardless of its concentration triggered higher defoliation compared to Fe-EDTA. Consequently, higher defoliation improved light interception of fruits and accumulated more anthocyanin. Particularly, Cu-EDTA could target mainly fruit cluster leaves which affect directly light interception of the fruits, i.e. more selective defoliants compared to Fe-EDTA. However, 3% Cu-EDTA rather defoliated excessively, accompanying with reduction of fruit weight and soluble solids. Therefore, our results suggest that 1% Cu-EDTA which defoliates properly the fruit cluster leaves could improve coloration and quality of ‘Hongro’/M.9 apple fruits.

Abstract
Introduction
Materials and Methods
    Plant Material and Treatment of Chelates
    Photosynthetic Changes of the Chelates-Treated Leaves
    Quality of Harvested Fruit
    Statistical Analysis
Results and Discussion
References

• Heon-Kyu Lim(Department of Horticultural Science, Chungbuk National University)
• Hyunsuk Shin(Department of Horticulture, Gyeongnam National University of Science & Technology)
• In-Chang Son(Planning and Coordination Division, National Institute of Horticultural and Herbal Science, Rural Development Administration)
• Youngjae Oh(Department of Horticultural Science, Chungbuk National University)
• Keumsun Kim(Department of Horticultural Science, Chungbuk National University)
• Sung-Il Oh(Department of Forest Genetic Resources, Korea Forest Research Institute)
• Sewon Oh(Department of Horticultural Science, Chungbuk National University)
• Daeil Kim(Department of Horticultural Science, Chungbuk National University) Corresponding author