Journal of the Japanese Society for Horticultural Science
Online ISSN : 1880-358X
Print ISSN : 0013-7626
ISSN-L : 0013-7626
Effects of Leaf Age and Defoliation on Growth at the Early Stage of Fruit Development in Satsuma Mandarin
Naosuke NII
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1978 Volume 47 Issue 2 Pages 172-180

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Abstract

1. The amounts of flower formation with special reference to the leafy and leafless flowers, and their fruit set were observed in three different orchards of satsuma mandarin (Citrus unshiu MARC.). In this experiment, flowers were divided into two morphological classes; leafless-shoot bearing a flower but no leaves, and leafy-shoot bearing a flower and leaves. On the individual secondary scaffold branch, the percentage distribution of leafless tends markedly more to produce on on-year tree than to do off-year tree. As the position in each tree crown shifts from the outside towards the inside, the percentage of leafy flower was significantly decreased. Leafless flowers on outside of on-year tree comprised 65 to 80 per cent of flowers. Leafy flowers set more fruit than leafless flowers. The percentage of leafy flowers decreases and that of their fruit set increases as the number of leaves per flowering shoot increases. Further, the chance of sitting fruit is greater as the ratio ofleaf area to a flower is higher.
2. To observe the effects of spring leaves (spring cycle leaves of the current year) or old leaves on flowering and fruit set, experiments were conducted with secondary scaffold branches of satsuma mandarin trees grown under field conditions. Treatments were the same method as described in the preceeding paper(16). Flowers bearing old-leaf gave the best development of ovary in weight at anthesis. The development of ovary reduced in the following order, no-leaf, control, and new-leaf plot. Fruit set for one month after full bloom were also greatest in fruit bearing old-leaf. Its ranking in the other plots was; control>no-leaf>new-leaf plots. Not only was the development of ovary in new-leaf plot the poorest among the four plots, most of the fruits abscised in this plot immediately after bloom. In the remaining three treatments, marked fruit drop was observed in early July, particularly, in old-leaf and no-leaf plots. The development of ovary derived from the leafless flowers is inferior to that of the leafy flowers. There was a tendency to increase ovary weight in the control and new-leaf plots as the number of leaves per a leafy flower becomes greater. Fruit set of leafy flower was also superior to that of leafless flower.
3. The effects of spring leaf on fruit growth, and anatomical changes during development were investigated throughout an early developmental stage of satsuma mandarin fruit. Relative growth rates of both fruit diameter and fruit weight had two peaks during a period from full bloom to an early developmental stage. Juice sac primordia appeared already at anthesis. At about the secondary peak of the relative growth rate of fruit growth, locule is full of juice sac. The period from the emergence of juice sac to the beginning of their remarkable elongation was referred to as the cell division period. After this time, the fruit grew rapidly. The increase of fruit growth typically occurred three weeks after full bloom, being one to two weeks behind the time maximizing the leaf area.

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