Detection of potato spindle tuber viroid from dahlia bulbs imported from Canada and its sequence characteristics

Potato spindle tuber viroid (PSTVd; genus Pospiviroid) was detected in dahlia (Dahlia sp.) bulbs imported from Canada during post-entry quarantine inspection. Complete genome sequencing identified three PSTVd variants, all of which were identical to variants previously reported from dahlias in Japan. Phylogenetic analysis showed that these PSTVd isolates clustered within a clade containing Japanese dahlia-derived PSTVd variants and were distinct from PSTVd variants previously isolated from potato in Canada. Comparative sequence analysis revealed that the identified variants shared nucleotide substitutions C42U, 63U64, and G201U that have been associated with mild pathogenicity. Tomato plants (cultivar Rutgers) inoculated with the Canadian dahlia-derived PSTVd isolates developed mild symptoms. Similarly, inoculated potato plants (cultivar Dansyakuimo) showed no obvious aboveground symptoms, whereas harvested tubers exhibited mild symptoms, including deformation and eye prominence. These findings provide evidence that PSTVd is present in dahlia tubers imported from Canada and suggest that the detected variants share a common origin with previously reported Japanese dahlia-derived PSTVd isolates.