Symptoms

• Symptoms on foliage

Symptoms of TSWV range from chlorosis, mottling, stunting and wilting to severe necrosis of leaf, stem and fruit tissues. However, symptoms may vary according to the condition and age of the plant, as well as environmental conditions.

Primary infections (i.e. occurring in the current year) may cause brown areas and necrotic spots, either round or in the form of concentric rings (photo 1). Necrotic lesions develop on petioles and stems and affected tissues dry up and then fall.

TSWV attack starts at the top of the plant, with symptoms ranging from discolouration or chlorosis of the top (photo 2). Stem necroses can also be observed.

When infected the previous year, the plants can suffer from leaf roll, leaf curl and necrotic spots (photo 3).

TSWV lesions sometimes have a necrotised appearance around a central green area.

• Symptoms on tubers

Deformed tubers may be observed with splits, cracks and dark spots on the surface or under the skin. TSWV can also induce external or internal concentric brown necrotic arcs (photo 4), dark spots or internal necrosis and rot in the tuber flesh (photo 5).