Symptoms

• Symptoms on foliage

The most typical symptom on the foliage consists of bright yellow or necrotic chevrons (photo 1), although it is rarely observed in field conditions.

Different forms of mosaic symptoms and mottling turning into necrotic spots may also be observed (photo 2), quite often on leaves with a single stem (hence the name “stem mottle”).

With some cultivars, notably Santé and José (Wilja), the infection may become totally systemic and associated with the presence of necrotic leaf spots, sometimes with a halo (photo 3), and sometimes yellowing of the entire plant.

• Symptoms on tubers

The most typical symptoms of TRV are usually found inside the tubers, in the flesh (photos 4 and 5). These are quite marked brown necrotic arcs or more irregular wavy lines (photos 6 to 11), which can widen out to form spraing or corky spots sometimes extending over a large part of the tuber.

Superficial necroses can sometimes be found (photos 12 and 13). These can form rings centred on the lenticels. They are generally not typical enough to allow a definite diagnosis. When cut, the tuber shows that these lesions are not always related to internal necroses and that they may remain localised at the periderm.

TRV disease is recurrent in many potato producing countries and losses can be high in some years in some production areas. Internal tuber necroses, also known as spraing, are often due to TRV, but they may also be associated with Potato mop-top virus (PMTV) or following abiotic stress (physiological rust).