EFFECT OF LATE-SEASON TRUNK STRANGULATION ON FRUIT-QUALITY, RETURN BLOOM AND FRUITING IN POMELO TREES GROWN IN A PLASTIC HOUSE

Young 'Tosa Buntan' pummelo (Citrus grandis (L.) Osbeck) trees on trifoliate orange rootstock grown in a plastic house were used in this trial. The leaf to fruit ratio in each tree was adjusted to a range between 25/1 and 30/1 by hand-thinning in early June, 1991. The trunks were strangulated to 50 and 70 Kgf.cm with steel wire (1.6 mm diam.) in late October. The steel wire was removed 3 months later. The girdles left by the wires around the trunk disappeared completely after mid-june. The soluble solids contents and acid in the juice of fruits harvested in February, 1992, were highest in the 70 Kgf.cm treatment. As the wire tension was increased the carbohydrate content in leaves increased, whereas the nitrogen content decreased. This resulted in a higher C-N ratio in the leaves at harvest. The majority of flower buds which sprouted were leafy ones. The numbers of inflorescences and flower buds in the 50 and 70 Kgf.cm treatments were 4.9 to 6.4 times larger, respectively, than were those of the control. The percentage of fruit set ranged from 50 to 68 in each tree ; no significant difference was noted among the treatments. Spring shoots were slightly shorter in the 70 Kgf.cm treatment, but the number of spring shoots was almost the same in all treatments.