Vol. 70 No: 1

Title:
Trunk Strangulation and Winter Heating Effects on Fruit Size, Internal Quality and Maturation of ‘Tosa Buntan’ Pummelo Grown in a Plastic House

Author:
O.K. YAMANISHI

pp: 65-74

Abstract:
The effects of trunk strangulation and winter heating on fruit growth, internal quality and maturation were studied. Strangulation of the trunk with a steel wire (1.6 mm diameter) was performed to the depth of the wire diameter in mid-October 1992. A significant increase in fruit size took place one month after treatment. Stomatal conductance, transpiration and net photosynthetic rates of the leaves were significantly decreased by trunk strangulation, but degreening of the fruit rind was not affected. Specific dry weight of the spring leaves significantly increased 57 d after treatment. The consequent increase of total soluble solids (TSS) in juice was attributed to an increase in the sucrose content, and occurred two months after imposing the treatment. The decrease in titratable acidity (TA) was ascribed to the decrease in the citric acid (CA) concentration, while malic acid (MA) increased from mid-October to mid-December and decreased thereafter. As malic acid content was significantly increased by strangulation, total acid content did not differ among the treatments. The ratio of TSS-TA significantly increased, and conversely the CA-MA ratio significantly decreased, in the juice of strangulated trees as fruit ripened in the two temperature treatments. Based on these ratios, the strangulation treatment hastened maturation of pummelo by 2–3 weeks. The cumulative effective temperature required to harvest fruits with high internal quality was a minimum of 3,000 C day-degrees. The higher temperature regime gave significantly larger fruits with less rind degreening, higher internal quality and faster maturation than the lower temperature.

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