from 33 countries deposited in NCBI GenBank, showing that the virus is a great international traveler. The long-distance transmission among countries is most likely in plant materials carried by human. Phylogenetic and population genetic analyses indicated that the common ancestor of current PNRSV isolates was originated from America continent. Management and control The most important measure in controlling PNRSV is through planting of certified virus-free trees. Tree nurseries producing propagative material can use thermotherapy (keeping cultures at 38˚ C for at least 20 days), and/or apical meristem cultures to eliminate PNRSV. Prompt removal of infected trees is often recommended as a control strategy, but is not practical for most growers. Field studies have shown that planting of same or similar cultivars near an infected orchard favored earlier infection than when different cultivars were grown, indicating that planting of unrelated cultivars could help slow spread of the virus and allow healthy trees to bear fruit before infection. Genetically engineered resistance may be a possibility for control in the future using RNA interference silencing. References External links ICTVdB - The Universal Virus Database: Prunus necrotic ringspot virus Family Groups - The Baltimore Method Bromoviridae Viral plant pathogens and diseases Hop diseases Rose diseases