Risk factors

The vector, the fungus, O. brassicae, is favoured by moist, even excessively moist, soils and relatively low temperatures (10-20°C).

The virus does not persist in resting spores of the fungus, formed in unfavourable conditions. The mode of transmission to the potato is unclear, but with the other host species the root system is clearly the primary site of penetration.

Systemic infections of the potato are rare and infected tubers produce healthy plants (stems, leaves and daughter tubers).

It has never been possible to reproduce the symptoms in the tuber by mechanical transmission.

Outbreaks of TNV on potatoes have occurred in North America, Europe and Mediterranean areas but the reasons for these sporadic epidemics are unknown.