| Summary: | 碩士 === 國立屏東科技大學 === 熱帶農業研究所 === 89 === The purpose of this experiment is to regulate the flowering by chemicals and study their effects on fruit quality of longan (Dimocarpus longana Lour.). The research showed that the ingredients of firecrackers could induce the flower of longan, and potassium chlorate is the only effective chemical in firecracker.
Soil drench under canopy was used to force longan flower in previous study. However, the efficiency and timing were not as expected. To improve the efficiency of the chemical treatment, spray of mixed potassium chlorate, urea, and potassium biphosphate were applied. The results showed spray of potassium chlorate was more effective and faster. Foliage spray is found to be more convenient and lower cost to induce the flowers of longan.
Lower fruit set was found in off-season longan flower in the winter. Pollen germination under various temperatures was conducted to clarify the factor of low fruit setting. The results indicted that the optimal temperature for pollen germination were from 20℃ to 30℃. The percentage of pollen germination were 0.35% and 89.7% for 15℃ and 30℃ respectively. However, the rate of germination at 15℃ was the same as 30℃ at 3 hours after treatments. The result showed the effect of low temperature on fruit set might not so significant as expected.
Effects of chemicals on inflorescence and flower sex were also studied to realize the possible factor of low fruit set. It appeared that sexual sequence of longan was the same either for regular or off-season flower. The sequences of flowering were male flower, then hermaphrodite functions as female (HFF) and hermaphrodite functions as male (HFM). In some special conditions, HFF may flower first and thereafter produce earlier fruit when harvest. The result showed that chemical treatments did not significantly change inflorescence and flower sex ratio.
To understand the effect of different flower period on fruit quality in longan. Regular and off-season fruits from Wufong, Taichung, Yujing, Tainan and the NPUST campus orchard were harvested respectively. The fruit quality expressed as fruit weight, fruit diameter, the percentage of fruit peel, the percentage of flesh, and the percentage of seed, soluble solid concentration and favor were measured of normal. The percentages of fruit peel are higher in off-season fruits. The percentages of seed and flesh were higher in regular season. Flesh percentage is also higher in normal fruits. Fruit weight and diameter of normal and off-season fruit were not significant different. The soluble solids of all fruits tested were higher than 19∘Brix and no significant difference were found between treatment. The results indicated that fruit quality of off-season fruits were similar to those of regular season.
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