Vol. 70 No: 1

Title:
Trunk Strangulation and Winter Heating Effects on Carbohydrate Level and its Relation with Flowering, Fruiting and Yield of ‘Tosa Buntan’ Pummelo Grown in a Plastic House

Author:
O.K. YAMANISHI

pp: 85-96

Abstract:
Two plastic houses (PHs) at different temperatures were used to study the promotive effect of strangulation on flowering through carbohydrate level in leaves of eight year old ‘Tosa Buntan’ pummelo (Citrus grandis (L.) Osbeck) budded on trifoliate orange. The maximum and minimum temperatures in the PHs were set at 30°/15°C and 25°/5°C from 1 November 1992 to 30 April 1993. Strangulation of the trunk with wire of 1.6 and 2.0 mm diameter was performed to a depth of the wire diameter in October 1992 and 1993, respectively. The wire was removed four months later. At 25°/5°C, sugar and carbohydrate contents in leaves were, respectively, 4.1 and 2.8 times higher than at 30°/15°C in mid-February. Nitrogen content in the leaves was significantly decreased by strangulation after December. At 25°/5°C, there were significantly more sprouting shoots and flowers than for those at 30°/15°C. Flower density was increased significantly by strangulation at both temperatures. Their chief increase was due to more leafless flowers. Under 30°/15°C, anthesis was hastened to 20–28 d and fruit diameter was 40% larger than that at 25°/5°C in early June. Sucrose and malic acid contents in fruit juice were increased by strangulation for two consecutive seasons. In strangulated trees, yield was 1.4–1.5 times larger in the season following treatment as a result of more fruits. The results showed that leaf carbohydrate content could not account for the promotive effect of strangulation on flower induction and initiation; but their level at the time of flowering seemed to be directly related to the ensuing growth and yield. Trunk strangulation in late season, however, increased the number of diffentiated flowers, hastened fruit enlargement, improved fruit internal quality and enhanced yield of ‘Tosa Buntan’ pummelo regardless of environmental conditions and leaf carbohydrate concentrations.

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