Symptoms

• Symptoms on foliage

The symptoms are not always very apparent during the growing season. Indeed, they appear quite late in the season, often at the same time as the senescence of the plants.

The first symptoms are characterised by wilting of the basal leaves, which curl up and turn yellow. The symptoms then spread rapidly to the apex (photos 1 and 2).

The wilting is not always accompanied by the discolouration of all the leaves. Sometimes, only discolouration located between the veins can be observed.

Some cultivars develop forms of dwarfism or internodes with malformed terminal leaves.

• Symptoms on tubers

The expression of the disease on tubers is characterised by a yellowish to brown colouration of the vascular ring often starting from the stolon-end. If pressure is applied to the tuber, the vascular ring may exude a cream-coloured ooze formed by the bacteria and the decomposed plant cells (photo 3).

In an extreme phase the tuber is cracked on the surface and dark marks appear under the periderm. It then decomposes without any particular smell and a cavity may form inside (photo 4).