Abstract
The relationships between fruit load, fruit size, shoot growth and dry matter productivity of leaves were investigated with 5-year-old trees of Miyagawa Wase, an early ripening satsuma mandarin, grown under field conditions. After the fruits were harvested, 16 sample trees were dug out and various tree components such as current and older leaves, current shoots, older branches and roots were separately weighed. The growth of older branches during the last year was estimated based on their diameter and length measured two times at the time of sampling and one year before. As an indicator of fruit load, fruit number per kg of dry leaves in each tree was defined as “index of fruit load”.
1. The total annual growth increment per tree (fruits+new leaves+current shoots+increment of older branches+increment of roots) was positively correlated with the total amount of leaves per tree.
2. The production of both new leaves and current shoots per unit leaf biomass (1kg in dry weight) was found to decrease with increasing indices of fruit load.
3. Higher index of fruit load resulted in the reduction of average fruit weight and the remarkable promotion of fruit productivity per unit leaf biomass. The trees bearing 1 fruit per 40-60 leaves, which was approximately equal to or slightly less than the normal level of fruit load in ordinary commercial orchards, produced 1.0-1.1kg of fresh fruit per m2 of leaf area.
4. The annual growth increment per kg of leaves (nearly equal to the dry matter productivity of leaves) was 2.3-2.5kg/kg leaf•yr in extremely light bearing trees, while it increased up to about 3.7kg/kg leaf•yr with increasing fruit load in most heavily loaded trees.
5. The relationships between the fruit load and average fruit size or fruit yield per unit leaf biomass seemed to be more or less similar to those between planting density and mean plant weight or yield per unit area proposed by Shinozaki and Kira (23). The quantitative formulation of the latter relationships, however, was inapplicable to the former case.
