Effects of different fruit thinning on alternate bearing, fruit quality and carbohydrate content of 'Harumi'

The purpose of this study was to find methods to obtain adequate amounts of fruit bearing and properly manage fruit bearing in order to stabilize fruit production from the successive cropping of 'Harumi'. Different methods for fruit thinning were studied to find their effects on alternate fruit bearing, fruit quality, and the carbohydrate content of 'Harumi' trees. 1. A fruit number of 40 or more per one cubic meter of canopy volume in a year resulted in a markedly decreased amount of flower setting in the following year; a fruit number of 10 or less in a year resulted in an excessive amount of flower setting in the following year. In the former case, leaves etiolated in the following July with old leaves defoliating markedly. When fruit harvest was controlled to 20-25 pieces per one cubic meter of canopy volume in a year, new shoot development and flowering were, good in the following year. 2. Compared with fruit thinning mainly for finish, fruit thinning mainly for coarse thinning early in July resulted in a higher ratio of fruit in the 2 L class, heavier dry weights of underground parts, and markedly increased amounts of carbohydrate accumulation in large branches and roots. The accumulated amount of carbohydrate in general, starch in particular, also increased in other parts of the trees. 3. Compared with alternate branch unit thinning, fruit thinning at the tips of the primary and secondary scaffold branches before early in July followed by finishing fruit thinning to control fruit harvest to 20-25 pieces per one cubic meter of canopy volume resulted in more stable flower setting and a larger number of fruit in the 2 L and L classes. 4. Unilateral thinning of fruit within the crown, by which about one half of fruit the primary and secondary scaffold branches on one side bore were removed from the trees, decreased fruit weight per fruit, increased the number of fruit in classes L and M, and, in the following spring, brought about excessive flower setting mainly on parts that were kept from fruit bearing in the previously year.