Abstract
Three-year-old Tosa Buntan (Citrus grandis (L.) Osbeck) trees grafted on trifoliate orange rootstock were grown in four plastic houses under different minimum and maximum temperature treatments. The minimum and maximum temperatures were as follows: 5-25°C, 10-25°C, 10-25°C, and 10-35°C from early December, 1987 to early May, 1988, and again controlled to 10-25°C from early December, 1988.
The two houses with controlled temperature regimes of 10-25°C and 10-35°C were left with their side-windows fully opened from early May to early December, 1988. On the other hand, the plastic film on the top of the other two houses with controlled temperature regimes of 5-25°C and 10-25°C was removed in mid-May and replaced in early December, 1988.
Temperature treatments in all plastic houses during the winter resulted in earlier flowering time with longer duration, and relatively high parthenocarpy. On leafy flowers, the greater the number of leaves, the higher the fruit set. High temperature during fruit development gave large fruit with pyriform shape and marked neck at the stem end, thicker peel, broken axial parenchyma and reduced TSS and citric acid contents in juice in late December, 1988.
Analysis of juice of fruit stored at 6-8°C and 85-90% relative humidity showed a slightly slower decreasing citric acid content than in fruit retained on the tree at a late stage of fruit development. However, the TSS content in juice and rind color were not influenced by either condition. Covering the plastic houses with plastic film throughout the year improved the rind color. It was estimated that the summation of effective temperature needed for fruit maturation of Tosa Buntan grown under plastic houses was about 2500-2600 C day-degrees.
