A Case Study on Crop Load to Avoid Alternate Bearing in Columnar Apples

Crop load to avoid alternate bearing was investigated in 5-12786 columnar apples. Alternate bearing started from three years after first bearing. For five years from the first bearing, more than 90% of trees whose crop load was smaller than three fruits per cm2 of the trunk cross-sectional area (TCA) showed increases in the flower bud number and yield. However, eight-years-old trees being thinned to give yield two–three fruits・cm–2 of TCA at 30 days after full bloom showed less than 10% terminal flower bud formation. Compared with treatment to distribute fruits throughout whole branches, the number of terminal flower buds decreased with treatment to localize fruits in parts of the tree. To predict the frequency of terminal flower buds, the best indicator of crop load was the fruitlet cluster/fruit ratio, and the fruiting part length/fruit ratio was the second. Regarding to habits of terminal flower bud formation, long vigorous shoots more frequently formed flower buds than spur-like shoots. Because fruiting shoots mostly consist of the latter, methods to promote flower bud formation of spur-like shoots should be developed. To understand adequate crop load of columnar apples, more varieties need to be examined while considering the influence of fruit distribution and the control of long shoots.