ウンシュウミカン成木の着果程度及び摘果が果実の大きさ及び形質, 翌年の着果などに及ぼす影響

Abstract

A group of 15-year-old trees of ‘Shigeta Unshu’, a midseason cultiver of satsuma mandarin, bearing various fruit loads under natural conditions, was selected as the non-thinned tree group. Another group of the same-aged variety with heavier fruit loads was thinned so that the loads were similar to the former groups. Non-thinned and thinned groups were compared to examine influences of fruit loads and fruit thinning on fruit characteristics, growth, flower bud formation in the following year and other parameters.1. The Brix of juice increased with increasing fruit load index (No. of fruit per 10, 000 leaves) in the thinning group. The difference between fruits with high and low fruit load indices, however, was small. In the non-thinned group the correlation between these two parameters was non-significant.2. In the lower range of fruit load indices, Brix was lower in thinned trees than in non-thinned trees with similar loads. For the same-sized fruit from each group, the Brix was lower from thinned trees than from non-thinned trees.3. Heavier fruit thinning resulted in a lower Brix value independent of fruit load.4. Acid concentration of juice changed very little with changes in fruit load indices in both groups.5. Partial correlations between acid concentration and the intensity of fruit thinning were very low. For similar-sized fruits, acid concentration was almost the same between both groups. The results suggest that acid content of juice was not affected by fruit thinning.6. Average fruit weight and the fruit growth index (ratio of diameter2×height of fruit on November 26 to that on August 8) decreased with increasing fruit load in both groups. The average weight and the growth indices were higher in thinned trees than in non-thinned trees with similar fruits loads.7. Heavier fruit thinning resulted in greater average fruit weight and higher fruit growth indices in both groups, irrespective of fruit load.8. There was no clear relationship between the number of leaves on summer-flush shoots and the fruit load indices, in both groups.9. Trees with low fruit loads had abundant flowers in the following year compared with trees with heavy fruit loads, in both groups. Number of flowers, however, was less in thinned trees than in non-thinned trees with similar fruit loads.