Abstract
Sugar and ascorbic acid (AsA) contents were determined in flavedo of fruits at growing stages, sampled from both the sunlit exterior area and the shaded dark interior area of the canopy, in a common and an early cultivar of satsuma (Citrus unshiu Marc. cvs. ‘Hayashi’ and ‘Miyagawa’) and in Hassaku (Citrus hassaku Hort. ex Tanaka), in order to clarify the effect of light intensity on sugar and AsA content.
1. The fruits from the exterior canopy were superior in diameter and weight to those from the interior canopy in each cultivar of satsumas and in Hassaku.
2. The sunlit exterior fruits were higher in carotenoid content in the flavedo than the shaded interior fruits in every stage, in both satsumas and Hassaku.
3. AsA content in the flavedo tended to increase with fruit growth in both satsumas and in Hassaku. At the later stages of fruit growth, however, this tendency became less or disappeared. High content of AsA in the flavedo was observed in the fruits from sunlit exterior canopy as compared with those from shaded interior canopy, in every growing stage in each cultivar. As the fruits grew, the difference in AsA content between the fruits from the two areas increased further in ‘Hayashi’, a common satsuma cultivar.
4. The predominant sugars in the flavedo were fructose, glucose and sucrose in both satsumas and Hassaku. Content of the sugars tended to increase with fruitgrowth. In the later stages of fruit growth, increase of sucrose was less and sometimes the content did not reach the limiting level, showing a similar trend to that of AsA. The sunlit exterior fruits were higher in content of sugars in the flavedo during the growing period than were the shaded interior fruits in all the cultivars.
5. In ‘Hayashi’, sugar and AsA contents in the flavedo and juice were determined after treatments of girdling, defoliation and application of growth regulators on the fruit surface. Significant positive correlations were found between sucrose and AsA content in the flavedo (+0.82) and in the juice (+0.95).
