Effect of Trunk Strangulation Degrees in Late Season on Return Bloom, Fruit Quality and Yield of Pummelo Trees Grown in a Plastic House.

Abstract

Seven-year-old 'Tosa Buntan' pummelo (Citrus grandis (L.) Osbeck) trees on trifoliate orange rootstocks grown in a plastic house were used in this study. The trunks were strangulated using 1.6, 2.0 or 2.6 mm steel wires at a depth of wire diameter in midNovember 1991. The wire was removed 3 months later. The enlargement of the trunk girth in the treated trees, especially in the 2.6 mm treatment, was smaller than that in the control. Specific leaf weight (SLW) of the previous year's leaves increased by treatment with 1.6 and 2.0 mm wires, but it occurred later in 2.6 mm treatment. Net photosynthetic rates (Pn) of the leaves, especially in the 2.6 mm treatment, decreased on treated trees. The numbers of inflorescences and flower buds on treated trees were much larger but shoot growth was reduced compared to control trees in 1992. Conversely, treated trees produced fewer flowers in 1993. The percentage of fruit set on treated trees ranged from 2.4 to 3.1% in 1992; no significant difference was noted among treatments. Fruits, harvested in February 1993, from the treated trees weighted less, had thinner peel, and higher contents of sucrose and citric acid in the juice than those in the control trees, but the yield and the number of fruits at harvest were, respectively, 1.4 to 1.6 times and 1.6 to 2.3 times larger in the treated trees than those obtained from control trees. The 2.6 mm treatment resulted in significant reduction in yield in 1994, whereas, the other treatments yielded as well as the control trees, the percent return bloom was significantly reduced. The wire sizes of 1.6 mm and 2.0 mm in diameter were suitable to strangulate the trunks of 7-year-old 'Tosa Buntan' pummelo trees.