Symptoms

• Symptoms on foliage

Early bacterial infections induce rotting of mother tubers and may be responsible for poor or non-emergence.

Blackleg is the most typical symptom (photo 1). It ranges from a dark brown wet rot of the lower part of the plant to dry necroses depending on weather conditions (photo 2). In some cases, only internal necrosis develops, sometimes associated with hollowing of the stem due to pith degradation (photo 3). Chlorosis and/or leaf wilting symptoms associated with blackleg (photos 4 and 5) enable the identification of diseased plants in infected fields.

Although humid conditions are favourable to the development of rot, warm dry conditions are more likely to cause wilting.

• Symptoms on tubers

Diseased tubers show soft rot, often extending from the stolon end into the tuber (photo 6). The wet rot presenting a granular consistency has a creamy-white colour or a brown to black colour near the margins of the diseased tissue (photo 7). Secondary saprophytic organisms developing in infected tissue cause nauseating smells and the formation of mucus. Lenticel rots are observed in the case of field conditions that are too wet or in high humidity storage conditions (photos 8 and 9).