Abstract
Two-year-old potted ‘Tosa Buntan’ pummelo (C.grandis (L.) Osbeck) trees grown in a plastic house (PH) were used in this trial. The trunk 15 cm above the graft union was strangulated with 1.6 mm diameter wire at a tension of about 30 Kgf. cm every month from August to November 1990. The duration of the strangulation treatment was 2 months for each treating time. Defoliation was severe and many leafless flowers sprouted at the upper part from the strangulation position (UP) during the winter season. All flower buds were thinned and defoliated previous shoots were pruned in early March 1991. New leafy flower buds resprouted at the UP. The number of flower buds and fruit set were higher at the UP than at the lower part (LP) . The recovery degree of girdle formed after the release of wire ring by mid-May was high in all treatments except for August treatment. Leaf number and area at the UP in mid September increased as the strangulation time was delayed, nonetheless, both were highest in control trees. The photosynthetic rate at the UP was the lowest in the control trees in mid-September and the highest in late November except for November treatment. Total sugar and carbohydrate contents in late August were increased as the strangulation time became early. On the contrary, nitrogen content was decreased and C/N value was increased as the treating time became early. November treatment produced larger fruit, while other treatments did not differ with the control trees. Coloration of fruit rind was improved in treated trees; however, no significant difference in TSS and acid contents was observed among treatments. The numbers of inflorescences and flower buds were higher in the treated trees than in the control trees and fruit set was not affected in the second year. Yield was lower in strangulated trees in the first year, but it was higher in the second year. Thus, the total yield in two years excluding the August treatment was 19-25% higher in strangulated trees than in the control one.
