| Summary: | 碩士 === 國立中興大學 === 園藝學系所 === 106 === The harvest season of most mandarins and tangerines in Taiwan is during November to March. On the other hand, lemon can be harvested annually, however, the yield in summer is much higher than spring which causes the price variation and affects the income of cultivators. It has been known that low temperature and drought can induce flower bud initiation in citrus. This research is aimed to study the effect of water deficit on flowering of ‘Ponkan’ mandarin and ‘Murcott’ tangor and the effect of water deficit combined with girdling on ‘Eureka’ lemon flowering and the quality of off-season fruits. The potting ‘Ponkan’ and ‘Murcott’ trees were subjected to water deficit for two months starting from September 2015. After two months of water withdraw, the soil water contents decreased from 54-60% to 5.7-5.9%. Both citrus varieties formed flower buds two weeks after re-watering. Same water deficit treatment was also applied in September 2016, however, no significant flower bud formation was observed in both varieties. In summer of 2016, field grown ‘Eureka’ lemon was treated with water deficit and girdling, flower bud formation was induced after ten weeks, but it was not significantly different from the control group and no significant difference in soil volumetric water content was observed between treatment and control group. When ‘Eureka’ lemon was observed was harvested in November, not only the fruit weight and size but also the ratio of total soluble solids to titrable acidity were higher. When the fruit was harvested in March, the content of ascorbic acid in fruit was higher and the peel color is greener.
The drought stress exerted the effects on growth and yield of crops. When ‘Ponkan’ was treated with water deficit to induce off-season flowering often developed wilited leaf and cause leaf falling. Results from the foliar application of 1.0 mM salicylic acid and 1.5 mM hydrogen peroxide to potting ‘Ponkan’ trees indicated that salicylic acid treatment could increase the starch content in leaves one week after application. After seven weeks of water stress, trees receiving salicylic acid treatment had higher drought tolerance than hydrogen peroxide treatment. The leaf relative water content, chlorophyll fluorescence were higher in salicylic acid treated trees and the electrolyte leakage percentage and hydrogen peroxide content in leaves were lower when treated with salicylic acid. Three weeks after re-watering, those trees treated with hydrogen peroxide showed sprouting in shoots and developed off-season flowers after on-season flowering was ended.
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