The Effect of Fruit Temperatures on the Maturation of Satsuma Mandarin (Citus unshiu Marc.) Fruits

The effect of fruit temperatures on the growth and compositon of satsuma mandarin fruits was investigated during maturation stage, by enclosing fruits on the tree grown under natural conditions in transparent acrylic cylinders whose inside temperatures were regulated at 15°C, 23°C and 30°C, respectively.Both a whole fruit and peel weights were greatest at 23°C and least at 30°C. But specific gravity of a whole fruit was much less at 15°C and 23°C then 30°C. Free acid content in the juice decreased more rapidly with an increase in fruit temperature. Total soluble solid and sugar content in the juice was highest at 23°C, followed by 30°C and 15°C in this order. In the peel, the lower the fruit temperature, the earlier the chlorophyll degradation and carotenoid accumulation occurred. However, chlorophyll degradation was inhibited and little carotenoid pigments developted at 30°C. ABA levels in the peel, also, began to rise at lower fruit temperatures and were lowest at 30°C. Coincident patterns of free ABA level and carotenoid content at respective treatments, particularly, indicate that ABA level in the peel may be involved in carotenoid synthesis which is affected by fruit temperatures. On the other hand, GA-like activities were not affected by fruit temperatures. These results suggest that temperature has influence on the maturation of satsuma mandarin fruits partly through its direct effect on fruits per se.