| Summary: | 碩士 === 國立臺灣大學 === 園藝暨景觀學系 === 107 === Oncidesa is one of the most important cut flowers in Taiwan, which generated an export value of 11.96 million USD in 2017. Low sale price in the high-peak harvest seasons (May-June and September-December) is a serious problem faced by growers in Taiwan. Therefore, finding an effective flowering regulation method is needed. On the other hand, research of postharvest physiology on Oncidesa cut flower is very important, since most of Oncidesa cut flowers produced in Taiwan are exported to Japan. Till now, no reference is available on the floret opening mechanism and nutrient mobilization within inflorescence in Oncidesa. Furthermore, related researches on Oncidesa are much more difficult because its inflorescence is a raceme.
To comprehensively understand the effect of new shoots excision on the growth, flowering and production period of Oncidesa Gower Ramsey ‘Honey Angel’, year-round new shoot excision was carried out in Taichung and Yunlin in the first experiment of this thesis. Results showed that new shoots excision treatment increased number of total vegetative buds in both districts, attributed to the emergence of vegetative buds from the second back shoot stimulated by new shoots excision. Although new shoots excision treatment did have some negative effects on the newly grown pseudobulb and inflorescence, including diminishing the growth of newly grown pseudobulb, shortening inflorescence height, and decline in the number of branches, cut flowers grading of excision-treated plants in several months occasionally increased (compared with their controls), which might be due to young and vigorous growing plants used in this experiment. We also found that temperature difference in Taichung and Yunlin is a key factor influencing the production period difference between the two districts. For the purpose of avoiding high-peak harvest seasons, new shoots excision treatment can be done on mid-June in Taichung during summer, same treatment should be advanced to mid-May to mid-June in Yunlin. In winter, growers in Taichung can perform new shoots excision in mid-October, while growers in Yunlin are suggested to do the excision in late-October but before mid-November to achieve the same flowering regulation effect.
In the second experiment of this thesis, we focused on the floret opening mechanism from the perspective of carbohydrate metabolism. With the bud maturing and opening, its fresh weight (FW), dry weight (DW), FW/DW ratio, concentration of glucose and fructose rose continuously, while concentrations of sucrose and water soluble polysaccharides stayed stable. In addition, concentration of starch increased dramatically after buds opened. With the opening of a single flower buds, while inflorescence was keeping in 100 mg·L-1 8-HQC vase solution (without any exogenous carbohydrate), its FW, DW, FW/DW ratio, concentrations of glucose and fructose increased continuously. Since concentration of starch did not decrease after 8 days, the increase soluble carbohydrates came from the breakdown of water soluble polysaccharides, or carbohydrates transported from other tissues and organs.
The third and fourth experiments were done to understand carbohydrate translocation/competition among buds, opened florets, and stalk within an Oncidesa Gower Ramsey ‘Honey Angel’ inflorescence, in the case of without any exogenous carbohydrate supplement. We found that the existence of basal florets improved the opening of upper buds in the late vase days (more than 11 days), but basal opened florets withered severely if upper buds existed in the inflorescence, which indicated nutrient might transport from basal opened florets to upper buds. During the early vase days (within 8 days), main stalk was a major carbohydrate source for upper buds. Although basal opened florets can be a carbohydrate source to upper buds in the late phase, it competed with upper buds for carbohydrates, when main stalk was an available source within an inflorescence.
New shoot excision experiment in this thesis providates useful information to Oncidesa growers in Taiwan. Experiments about florets opening mechanism and nutrients mobilization within an inflorescence are important basic researches in post-harvest physiology in Oncidesa.
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