Effect of crop load on the yield, fruit quality, and fruit mineral contents of ‘RubyS’ apples

Nay Myo  Win1   Dongyong  Lee1   Yang-Yik  Song1   Juhyeon  Park1   Young Sik  Cho1   Moo-Yong  Park1   Youngsuk  Lee1   Hun Joong  Kweon1   Jingi  Yoo2   In-Kyu  Kang3   Jong-Chul  Nam1,*   

1Apple Research Institute, National Institute of Horticultural and Herbal Science, RDA, Gunwi 39000, Korea
2Tree Fruit Research and Extension Center, Washington State University, Wenatchee, WA 98801, USA
3Department of Horticultural Science, Kyungpook National University, Daegu 41566, Korea


Crop load management in apple trees is important for achieving optimum productivity and crop value. Hence, we investigated the influence of different crop loads on the fruit quality, mineral content, and yield of the ‘RubyS’ apple variety. After 4 weeks of full bloom, the crop load was adjusted by hand thinning to different (5, 10, and 15 fruits·cm-2) trunk cross-sectional areas (TCSA), representing low, medium, and high crop loads. The low crop load increased the fruit size and weight, the development of the red-blushed area, and the peel color a* at harvest; however, it reduced the total number of fruits·tree-1 and yield compared with that of the other crop loads. The medium crop load improved the fruit weight, flesh firmness, and soluble solids content and reduced the fruits·tree-1 but did not affect the fruit size and yield. However, there were no significant differences in the titratable acidity and starch index among the crop loads. The fruit mineral content (phosphorus and potassium) was higher in the low and medium crop loads compared to the high crop load. However, the nitrogen, calcium, and magnesium contents in the fruits were not affected by the crop loads. Overall, this study suggests that a low crop load improves the fruit size and weight, but its effect on the quality and fruit mineral content is similar to that of a medium crop load. Therefore, the optimum crop load level for the ‘RubyS’ apple trees was approximately 10 fruits·cm-2 TCSA.

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