THE USE OF NAPHTHALENE ACETIC-ACID AS A FRUIT-GROWTH ENHANCER IN SATSUMA MANDARINE - A COMPARISON WITH THE FRUIT THINNING EFFECT

When applied shortly after the end of the June drop, naphthalene acetic acid (NAA) increases the growth rate of the fruit of Satsuma mandarin (Citrus unshiu Marc.), which results in a bigger fruit size at harvest without any undesirable reduction in yield. In a high-yield regular bearer orchard, the effect of this treatment on the sizing of the fruit is similar to that obtained when NAA is used as a thinning agent at an earlier stage of development of the fruit. The apparently higher response obtained through thinning as determined by the mean weight of the fruit at harvest, is mainly owing to the selective removal of the smallest fruit rather than to a higher stimulation of the growth rate of the remaining fruits. The comparative advantages of fruit thinning vs. the direct enhancement of the fruit growth rate under different conditions are discussed.