A Study on Labor Force Reduction and Fruit Quality with the Use of Substances Showing Thinning Effect in 'Fuji' and 'Arisu' Apple Varieties

Thinning is a common practice in apple production. Many thinning agents have been used to thin apples. The effectiveness of the agents depends on the apple variety and other factors such as orchard conditions or environmental ones. 'Fuji' is one of the apple varieties that is difficult to thin and has been stubborn with different chemical thinning agents. In this study we evaluate the effectiveness of the flower thinning effect agent (FTEA) on 'Fuji' (late maturing variety) and 'Arisu' (early maturing variety) apple qualities such as fruit weight, L/D, hardness, number of seeds, sugar content, and acidity. FTEA was sprayed at 70% bloom only one time. The fruit set rates of FTEA-treated ones were 34.8% for 'Fuji' and 19.9% for 'Arisu', while those of the control were 73.0% for 'Fuji' and 79.9% for 'Arisu'. Thus, the fruit set rates were 38.2-60.0% lower in FTEA-treated plot than the controls. The weight of the fruits also increased by 4.6-13.0%. However, there were no differences in acidity, coloring, seed number, russet and physiological disorders between the two groups. In addition, we noticed a significant increase in yield without any negative effects, and the results generally showed that FTEA has a significant effect on 'Fuji' and 'Arisu' apple fruits. For the stimulation effect of pollen tube elongation, the results indicated no effect of FTEA on pollen tube elongation in an in vitro experiment. FTEA treatment significantly reduced total cost and labor force of flower thinning activity in apple orchard as decreased 67.8% and 76.6%. These results showed that the effects of FTEA spray for flower thinning were significant for both 'Fuji' and 'Arisu' varieties for fruit weight, thinning cost, and labor force reduction.