Phylogeny of five predominant pospiviroid species in Belgium

In Belgium pospiviroids are routinely detected in various hosts. The most frequently found pospiviroids are: Citrus exocortis viroid (CEVd), Chrysanthemum stunt viroid (CSVd), Potato spindle tuber viroid (PSTVd), Tomato apical stunt viroid (TASVd) and Tomato chlorotic dwarf viroid (TCDVd). Apart from the high incidence of pospiviroids in latently-infected ornamentals, viroids have also been found in plants where they cause disease: PSTVd and TCDVd in tomatoes and CSVd in chrysanthemum. In order to gain more epidemiological data on these infections, this study has conducted phylogenetic analyses of Belgian isolates for each of these five pospiviroid species. PSTVd and CEVd-isolates show a clustering depending on host plant identity. This was not observed for TCDVd and TASVd. A very high degree of sequence similarity was noticeable for CSVd-isolates from various hosts. During the past decade, PSTVd and CSVd-infected mother plants have been systematically eradicated in Belgium after positive detection results, also when found in symptomless plants, leading to a decreased trend of these quarantine pests in the past few years. However, other non-quarantine pospiviroid species are still ubiquitously present in many ornamentals. Since these pospiviroids can be equally harmful to crops as the two quarantine pests PSTVd and CSVd, there is still a risk that transmission occurs from symptomless-infected ornamental plants to economically important crops in Belgium such as tomato, pepper and chrysanthemum.