Potato is an important and vegetatively propagated crop species that is affected by many viruses, which tend to build up in crops in subsequent cycles of vegetative propagation. Unlike diseases caused by fungi and bacteria, viral diseases cannot be contro lled with the use of fungicides or chemical agents. Once a plant is infected the only possible way to eliminate the virus is by meristem-tip culture in combination with heat-treatment. However, the downside of this method is that it is time consuming and laborious. During the last couple of years, great advances have been made in utilizing RNA silencing as an antiviral tool. High levels of resistance toward virus infection have been obtained utilizing this mechanism in transgenic plants, demonstrating the robustness of this defense response. However, due to the current negative attitude to transgenic plants, the full potential of RNA silencing as an antiviral tool has not been achieved. Nevertheless, the study presented in this proposal is collaborative e ffort between the International Potato Center and Bioforsk to further exploit this technology and develop a non-transgenic, RNA silencing-based method for the generation of virus-free planting material.