Studies on the control of alternate bearing in citrus. IV

Abstract

In order to control the alternate bearing of Satsuma orange, the effects of fruit thinning on the fruit growth and yield in the current year and on number of flowers, shoot growth and yield in the following year were investigated from 1935 to 1950. 1. The decrease in the yield of the current year by the fruit thinning was only slight, because of the increase in size of the remaining fruits. Increases in the number of flowers and yield were obtained in the following year. The total yield of the two succeeding years was increased and annual amount of crop obtained by the fruit thinning was nearly equal in the two years. 2. Removing all the fruits on a particular branch increased markedly the number of flowers and fruit set in the following year on the branch, and the larger the branch, the greater the effect of thinning. 3. It was found that the most desirable ratio of fruit to leaves for the current year's crop and the following year's fruiting was 20 to 25 leaves per fruit for Satsuma orange on trifoliate orange rootstock, and 15 to 20 leaves per fruit for the one on Yuzu (Citrus junos) rootstock. 4. The earlier the fruits were thinned (including flower thinning), the more the effect was, though the thinning even in as late as mid-November showed some effect. However, the appropriate time of fruit thinning for Satsuma orange seems to be the early part of August in Okitsu, as physiological fruit dropping has been over by the end of July. 5. Even when the number of flowers was increased by the fruit thinning in the previous year, the number of shoots and their growth were not decreased, but rather increased in most cases.