Establishment of full ripeness cultivation on tree system for wase Satsuma mandarin using rain protected greenhouse: (I) Effect of late fruit thinning on fruit quality, yield and the following year's flower formation

A study was conducted on how late fruit thinning of Wase satsuma mandarin in full ripeness cultivation on trees by using a rain protected greenhouse will affect fruit quality and the following year's flower formation. 1. Late fruit thinning was performed on Wase satsuma mandarins (line names: 'Miyagawa Wase', 'Okitsu Wase', and 'Obarabeni Wase') which were cultivated in a rain protected greenhouse so that the number of leaves per fruit might become 40. The fruit development, fruit quality, yield and ratio of the number of fruit were investigated by fruit sizing. The fruit diameter, as of September 20, was highly correlated with fruit diameter at harvest time and may be the indicative figures for fruit thinning done after late September. For every line, in the case of late fruit thinning, the yield was about half of that in the case of no fruit thinning. However, the average fruit weight at harvest was larger, and the ratio of small-size fruit (Size: 2S and 3S) was lower than when there was no fruit thinning. Regarding fruit quality at harvest, the level of peel puffing became higher while the Brix rose by more than 1. 2. Late fruit thinning was performed on Wase satsuma mandarin (line name: 'Miyagawa Wase') with number of leaves per fruit 40 to 30. The effects of the differences in number of leaves per fruit on the current year's fruit quality and following year's flower formation were investigated. As for the fruit quality at harvest, the Brix was higher than in fruit without fruit thinning. The fruit with a number of leaves per fruit 40 tended to be higher in Brix than in fruit with a number of leaves per fruit 30. The level of peel puffing was clearly higher in the case of 30. There was no big difference in yield. The following year, the flower formation was at a level of 2-3, or middle levels, of an evaluation scale of 1-5, in the case of late fruit thinning. In the case of no fruit thinning, the level of flower formation was the lowest, '1'. The flower formation in the case of a number of leaves per fruit 40 was better than that in the case of a number of leaves per fruit 30. 3. From the above, it was concluded that, in the case of full ripeness cultivation on the tree of Wase satsuma mandarin, late fruit thinning with a number of leaves per fruit 40 would be effective for the stable annual production of high quality fruit. It was also suggested that the fruit sizes that should be thinned on September 20 were 55mm and larger (Size L or larger at harvest) and 42mm and smaller (Size 3S or smaller at harvest).