Symptoms on tubers

Tubers show brown-black surface lesions with radial or reticulated cracks which may be confused with those of common scab, caused by bacteria of the genus Streptomyces.

Circular lesions and light brown plaques may also be observed, as well as blisters which form on tubers during storage (photos 1 to 4).

The symptoms caused by TNV are also called ABC-disease because of the initial description of the three types of symptoms induced by the virus:

- A symptom: black-brown blisters;

- B symptom: rots or deep sunken lesions developed in storage from the type A blisters;

- C symptom: scab-like pale brown lesions with star-shaped cracks to brown spots without cracks, visible at harvest.