Yield of Differently Trained Trees and Fruit Quality at Various Locations within Canopies of Differently Trained Satsuma Mandarin Trees

Abstract

In common Satsuma mandarin (Citrus unshiu Marc. cv. Sugiyama) trees of open center and hedgerow types, fruits at different locations within the tree canopy was examined from July to December, 1977, in order to obtain fundamental data for rationalizing the practice of tree form management such as planting system, tree form, pruning, etc., and also for improving fruit quality. Studies were also made on tree growth and yield from 1970 to 1977.
The following results were obtained.
1. Tree growth in trunk girth was a little better in the trees of open center type than that of hedgerow type, and tree crown enlarged progressively with years in the former while it was kept compact in the latter. Yield per tree of the open center type (which had a larger tree crown volume) was greater than that of the hedgerow type, but yield per 10a was greater for the hedgerow type because of higher planting density.
2. In either type of tree, respiratory rate of fruits decreased rapidly from the beginning of August to the beginning of September, and thereafter increased gradually up to the end of November. Little difference was observed in the respiratory rate among the fruiting locations within the canopy, except for interior fruits, which showed lower respiratory rate during maturation.
3. The fruits at the interior and at the top and skirt of the east and west sides were colored well, while those at the top and skirt of the north side were badly colored in the trees at open center type. In the trees of hedgerow type, the fruits at the top and skirt of the east side were well colored, but those at the interior and the top and skirt of the west side tended to have a bad color. Total carotenoid content in peel at the mature stage did not vary with fruiting locations in either type of trees.
4. Fruit weight at the mature stage was greater at the top of each side and smaller at the interior of the tree crown. No difference in fruit weight was observed between the two types of trees and among the quadrants of the canopy. A positive correlation (significant levels; p<0.05, and p<0.01) was obtained between fruit weight and cumulative solar radiation at each fruiting location up to the end of October. No correlation could be obtained between fruit weight and air temperature or fruit temperature.
5. In either type of trees, degrees Brix of fruit juice at mature stage differed little among fruiting locations, although it was slightly lower at the skirt and interior of the canopy. Moreover, a positive correlation (p<0.05, p<0.01) was obtained between cumulative solar radiation during the mature stage and Brix degree. Between degrees Brix and cumulative air temperature, there was a negative, but not significant correlation up to the middle of November, but there was a significant (p<0.05, p<0.01), positive correlation from the end of November to the middle of December. Between degrees Brix and cumulative fruit temperature, significant, positive correlations were often recognized up to the end of November, and at the middle of December, the correlation became stronger and the degrees Brix tended to increases with fruit temperature.
6. The titratable acidity of fruit juice at the mature stage, did not differ among fruiting locations within the canopy except that it was lower at the interior of the tree. There was a non-significant correlation between titratable acidity and cumulative solar radiation, cumulative air temperature or cumulative fruit temperature.
Thus, it appears that at least in the Seto Inland Sea area, fruit quality expressed by degrees Brix and titratable acidity is little affected by the variation in microclimate varying with fruiting locations within the tree canopy in either type of trees used.