Potato X virus. Coloured transmission electron micrograph (TEM) of particles (green/blue) of the potato X virus. Potato X is a member of the potexvirus group that infects potato plants. It possesses long, filamentous particles that are transmitted by physical contact between healthy and infected plants. The use of virus-free propagative materials can control the spread of the virus. Potexviruses cause mosaics (patches of yellow or green colour) or ringspots (yellow circles with green centres) to develop in infected plants. Magnification unknown.