Effect of bearing angle of satsuma mandarin fruit on rind roughness, pigmentation, and sugar and organic acid concentrations in the juice.

摘要

The effects of the bearing angle of satsuma mandarin (Citrus unshiu) fruits to the branch (upward or sideways) on rind roughness, pigmentation, and sugar and organic acid contents were investigated in Japan. The rind surface of sideways fruits became smoother as the fruits grew, whereas upward fruits developed rough skins until late September. The time course curve of 'roughness value' (a plot of the numerical score of rind roughness transformed with an image analyser) was examined for each treatment. Although upward fruits and those from lightly cropped trees had rough surfaces, they differed physiologically in that upward fruits became smooth between early August and late September, and fruits from lightly cropped trees remained rough into lateOctober. Histological observations showed that rough rind had convex protrusions just above or between oil glands. Those above oil glands were frequent on mature fruit surfaces, and those between oil glands occurred on immature fruits. Similar protrusions occurred on upward bearing fruits and on fruits from trees with a low crop load. Compared with rough rind fruits, those with smooth rinds contained more sugars from mid-September to harvest and less organic acid from early August to early September. Just before rind became smooth, chlorophyll in the skin reached a maximum level and then decreased rapidly. Carotenoid synthesis began when chlorophyll concentration attained its maximum level, and continued to increase until harvest on 5 December. The 3 growth stages of fruits are described: (1) (sideways fruits, flowering to mid-July; upward fruits, flowering to early August) the rind roughens, the sugar and organic acid concentrations in the juice are low; (2) (sideways fruits, mid-July to mid-September; upward fruits, early August to late September) the rind becomes smooth and organic acid accumulates rapidly in the juice sacs; and (3) (sideways fruits, mid-September to harvest; upward fruits, late September to harvest) the rind becomes smoother andthin, the juice sacs accumulate sugars rapidly while organic acids decrease. It is concluded that the onset of stage 3, when the skin roughness disappears, is a significant stage of fruit maturation.