Effect of Controlled Fruit Temperature on Maturation of Apple Fruits

Abstract

Using 2 apple cultivars, ‘Golden Delicious’ and ‘Fuji’, each grafted on M7 rootstocks, the effect of controlled ambient temperature around the fruit on maturation of apple fruits was investigated during maturation stage. On-tree fruits were enclosed in acrylic cylinders whose inside temperature was regulated at 14°C, 21°C and 28°C for ‘Golden Delicious’ and at 10°C, 17°C and 24°C for ‘Fuji’.
1. Fruit weight of ‘Golden Delicious’ was greater at 21°C than at other temperatures, but that of ‘Fuji’ was not affected by fruit temperature.
2. Shape index of fruit (length/diameter) was highest at highest fruit temperatures in both cultivars.
3. Total sugar content in the flesh of ‘Golden Delicious’ was generally increased with increasing fruit temperature, while that of ‘Fuji’ was highest at 24°C, followed by 10°C and 17°C in that order.
4. In both cultivars, the lower the fruit temperature, the more sucrose and the less fructose and glucose accumulated. On the other hand, the level of sorbitol was not affected by fruit temperature.
5. Malic acid content in the flesh was generally decreased with increasing fruit temperature in both cultivars.
6. Anthocyanin content in the skin of ‘Fuji’ fruit was highest at 10°C, followed by 17°C. However, anthocyanin accumulation was inhibited at 24°C.
7. These results suggest that the maturation process of apple fruit on the tree is directly affected by fruit temperature per se late in the season.