Influence of Fruit Load Just Before Fruit Thinning on Fruit Size, Yield and Flower Bud Formation in Satsuma Mandarin

Abstract

The influence of fruit load index (FLI) (fruit number per 10, 000 leaves) just before fruit thinning on the average fruit weight and fruit yield in that year, and on flower bud formation in the following year were investigated in three cultivars of satsuma mandarin. Fruit thinning methods to improve the uniformity of fruit harvested from each tree group including trees of various FLI just before fruit thinning were discussed.
1. When fruit were thinned to the same FLI, the FLI just before fruit thinning scarcely influenced average fruit weight of the trees of ‘Hayashi Unshu’, (a late ripening cultivar). However, there was a significant negative correlation between those two parameters, resulting the differences of 20 to 30g in average fruit weight between trees of 300 and 1, 100 FLI just before fruit thinning, in ‘Okitsu Wase’ and ‘Miyagawa Wase’ (both early ripening cultivars).
2. Fruit yield per 10, 000 leaves increased greatly with increasing FLI in the nonthinned tree group, while yield in the trees of higher FLI just before fruit thinning was slightly lower in each tree group thinned to the same FLI.
3. If trees have excessive flowers or have a high FLI just before fruit thinning in a certain year, this is likely to decrease average fruit weight and fruit yield in that year at any FLI after fruit thinning.
4. The trees with fruits thinned to lower FLI flowered in the following year more than non-thinned trees of a similar FLI just before fruit thinning. Within each tree group thinned to the same FLI, the amount of flowers decreased with increasing FLI just before fruit thinning.
5. Tees with more than 700-800 FLI just before fruit thinning seldom flowered well enough to gain sufficient yield in following year, even if they were thinned severely.