Fruit-growth and Acid Content of Satsuma Mandarin in Relation to Flowering Time

Abstract

Fruit development of satsuma mandarin (Citrus unshiu Marc.) and the juice constituents were investigated throughout the growing season to elucidate the factors which determine the quality of fruit with special interest in the relationships between the time of flowering and the acid content of the fruit. In 1978, 8 trees growing in the experiment orchard of Okitsu Branch, Fruit Tree Resarch Station, were investigated. Leafy flowers, each floral branch bearing one flower and 2 to 4 new leaves, were classified into three groups according to the time of flowering-early flowers (5 days before full-bloom), intermediate flowers (full-bloom) and late flowers (5 days after full-bloom). The date of full-bloom of investigated trees was May 24.
1. The earlier the flowering time the earlier the commencement of physiological fruit drop, but there was no distinct difference in the date of peak of the drop among the three groups of flowers. Intermediate-flower-fruits completed the drop first. Intermediate-flower-fruits dropped about 50 percent of their fruit which was about 15 percent less than the drop of early or late-flower-fruits.
2. The rate of increment in fruit diameter was the highest on late-flower-fruits and the lowest on early-flower-fruits. It appears that the late-flower-fruits grow faster and recover the delay in relative growth. This is apparent on the longitudinal diameter of fruit as compared to the transverse diameter. Consequently, the shape index of late-flower-fruits went low very rapidly during the period from flowering to 60 days after flowering.
3. The later the flowering time the fewer the number of juice sacs per 100g pulp, and accordingly, the size of the juice sacs of late-flower-fruits was larger.
4. There was no difference in Brix of fruit among the three groups of flowers until late October. After that period there was a slight tendency for higher Brix in the fruits from earlier flowers. Coloring of rind commenced in late October and the fruit from earlier flowers showed advanced coloration.
5. Early-flower-fruits began to decline in free acid concentration first. Five days delay in flowering resulted in five days delay in the decrease of free acid. The difference in free acid concentration among the group of flowers was maintained through most of the growing season. Citric acid showed the same transition pattern as free acid. It was concluded that the acidity of mature fruit was determined principally in rather a short period before or after flowering.
6. Concentration of malic acid declined until mid-September and stayed stable thereafter. The rate of malic acid showed the lowest value in late September and there was no difference in the date among the groups of flowers.