Overview of Citrus Exocortis Viroid and Hop Stunt Viroid in Taiwan

Two previously reported citrus viroids, Citrus exocortis viroid (CEVd) and Hop stunt viroid (HSVd), represent main threats to the citrus industry in Taiwan. However, studies on these citrus viroids remain largely to be explored. To establish study about the current status of the citrus viroids in Taiwan, we focused on development of multiplex detection, disease ecology of the citrus viroids, and interaction between the two citrus viroids. In multiplex detections, our field-survey assay revealed that HSVd was more prevalent than CEVd and The two viroids commonly co-existed within the citrus cultivars. Results of the multiplex quantitative analysis showed uneven distributions of both viroids within different plant tissues such as twig bark. In disease transmission studies, both viroids were detected only rarely on seed coats, seed membranes and inner seeds, suggesting that these two viroids do not exhibit seed-borne transmission in citrus hosts. For interaction studies, our results demonstrated that the two viroids have a positive relationship and a similar infection pattern, while displaying titer enhancement and localization similarity with no symptom aggravation.