Molecular characterization and eradication of new potato spindle tuber viroid isolates from dahlia plants in Japan

Recently, the distribution of seeds and seedlings has expanded worldwide due to the internationalization of agricultural products. Quarantine-notifiable plant pathogens including viroids are therefore spreading globally, which is a major concern in terms of plant protection. Viroids are the smallest known plant pathogen and have a large host range, causing various disease symptoms after infection. In 2011, the Potato spindle tuber viroid (PSTVd), belonging to the Pospiviroid family, was detected in Akita Prefecture (North Japan). By 2015, unregistered PSTVd isolates had been identified in seven dahlia cultivars (a total of about 5000 plants) when leaves were surveyed in the fields where PSTVd was first detected. The newly discovered PSTVd isolates are very similar to a PSTVd dahlia isolate that was found previously in Japan. None of the infected dahlias showed disease symptoms during the early stages of infection, however, growth suppression occasionally occurred during later stages. At present, PSTVd appears to have been successfully eradicated from Akita prefecture, but the threat of new PSTVd isolates spreading to other susceptible hosts, such as tomatoes and potatoes, still remains.