Both viruses and bacteria are common and often latently – i.e. not visibly – present. The 4×50 tuber test is a standard test used to determine infections, especially in high-quality starting materials.
A sample of 200 tubers are supplied with a sample form for the survey. Four samples of 50 tubers are examined for PVY virus, for Pectobacterium and Dickeya or tobacco rattle virus (TRV).
It is also possible to carry out a 2×100 inspection on a sample of 200 tubers for the nematodes Melodoigyne fallax and chitwoodi. Different combinations are possible; this can be indicated on the sample form.