Symptoms

• Symptoms on foliage

The intensity of the symptoms and the speed of their appearance depend on the host (age, species, cultivar), on the inoculum (quality and quantity) and on the environmental conditions (temperature, moisture, type of soil, etc.). As a result, the symptoms in growing crops are not always obvious and usually start with the crinkling of a few leaflets (photo 1).

In the first stage of the disease wilting is visible only at the warmest time of day and may affect only one or two stems (unilateral wilt), then it finishes by spreading to the entire plant (photo 2).

With a severe attack, a bacterial exudate oozing can be observed at the leaf axils or from the vascular tissues of cut-off stems (water glass test: photo 3)

• Symptoms on tubers

Symptoms on tubers are characterised by the browning of the vascular ring, which is visible once the tubers have been cut off. A beige, then brown, rot (which explains the name of the disease) develops at the vascular ring (photo 4) and the tuber finishes by decomposing. Cutting (and pressing on) the tuber reveals a creamy fluid exsudate oozing from the vascular tissues (photo 5).

The exudate may also ooze out of the eyes or from the stolon-end attachment of infected tubers; the emergence of the bacterial ooze is visible externally by the formation of crusts with soil particles adhering (photos 6 and 7).