| Summary: | 碩士 === 國立臺灣大學 === 植物病理與微生物學研究所 === 103 === Viroids consist of solely non-coding ssRNA (249-401 bp) and frequently form secondary structure by intramolecular interactions. They are known as the smallest plant pathogens and infect a wide variety of crops. In spite of its small and simple property, plant viroids cause a great deal of agricultural loss. Citrus is one of the most important crops, of which numerous cultivars are susceptible to several viroids. In Taiwan, two plant viroids have been reported, namely Citrus exocortis viroid (CEVd) and Hop stunt viroid (HSVd). Nevertheless, Citrus bent leaf viroid (CBLVd), Citrus dwarf viroid (CDVd), Citrus bark cracking viroid (CBCVd), Citrus viroid V and VI (CVd-V and VI) are also reported globally to be able to infect citrus crops worldwide. The molecular biology technique reverse transcription polymerase chain reaction (RT-PCR) is commonly employed to detect the citrus viroid. Complex infections can generally be found in citrus crops. Due to the fact that a single plant may be infected by multiple viroids simultaneously, the present detection method for citrus viroids is time-consuming and laborious. Thus, the purpose of this study aims to improve the detection technique for multiple citrus viroids in a time-saving and cost-effective manner, thereby facilitating the field survey and inspection of citrus viroids. The study concludes a survey of citrus viroids over various locations in Taiwan, including Hsinchu, Changhwa, Douliu, Chiayi, Pingtung, Yilan, Hualien and Taitun. Our result suggests that rather than CEVd and HSVd, additional three viroids, CBLVd, CDVd and CBCVd, might also exist in the citrus fields of Taiwan. In addition, via phylogenetic analyses, we suspected that CEVd exists in Taiwan for a long time to form two specific clades, whereas other 3 detectable citrus viroids might be imported in recent years from all over of the world.
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