Clavibacter michiganensis subsp. sepedonicus
Causative agent and transmission
Clavibacter michiganensis subp. sepedonicus (formerly called Cory-nebacterium sepedonicum) is the causative agent for bacterial wilt on crops and ring rot on tubers.
This bacterium can easily survive on plant waste, on agricultural tools (harvesting and conditioning) and in all types of premises. It is also transmitted by the seed potato.
The disease develops most frequently in cool and damp weather and is of concern in areas such as northern Europe, Canada and the Far East.
Description of symptoms on crops
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The symptoms are not always easily visible on crops. However, wilting of the foliage may be noted on some plants, occurring quite late, with yellowing, coiling and necroses of the foliage, unlike Ralstonia. This wilting is not combined with discoloration of the whole leaf since only areas between the veins are discoloured.
Description of symptoms on tubers
Disease on the tubers is expressed by browning of the vascular ring starting at the stem-base which then develops into soft rot (not damp). The tuber must be cut crosswise to enable observation of the symptoms.
Pressing the tuber causes a yellowish-white bacterial exsudate to ooze out from the vascular tissues.
Severe attacks can cause cracking on the surface.
This parasite is classified as quarantine-regulated and is subject to compulsory control measures.
The use of certified seed potatoes that have undergone health checks remains the best guarantee.