When producing planting material, it is essential to start with a clean stock. This is commonly achieved by screening all material by PCR tests, but in part this can be achieved by using indicator plants for pathogen (virus) detection.

A limitation of PCR is that the biological relevance cannot be determined when detecting a virus. With indicator plants we can determine whether a virus is biologically active. It should however be noted that not all viruses can be detected with indicator plants, it is limited to viruses that can be mechanically transmitted.