Clavibacter michiganensis

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Clavibacter michiganensis cells (SEM) (click on image to enlarge it)
Author(s): Solke H. De Boer, Canadian Food Inspection Agency
Source: PaDIL

Clavibacter michiganensis (Smith 1910) Davis et al. 1984

The bacterium is wide-spread, Gram-positive, non-sporulating and causes several important crop diseases, mainly in temperate areas. The cells are rod-like and about 0.5-1.0 µm long. It spreads through small wounds and is easily transmitted through farming tools or seeds. It invades the xylem vessels of the host plant, causing wilts, cankers and rots.

C. michiganensis survives for several months in plant residues or seeds. Management methods include the use of uninfected seeds or plant materials and chemical control. Several subspecies of this bacterium have been described which cause diseases on specific crops. The two most important ones are:

Clavibacter michiganensis subsp. michiganensis (Smith) Davis et al. causes bacterial canker of tomatoes which is characterized by wilting and canker lesions on the stem. Other symptoms are clearly defined brown leaf spots or leaf curling. Fruits may have "bird's eye spots" which are raised areas with a dark centre and a white halo. Plants may survive but yield will be reduced. Latent infections are also common. This subspecies has quarantine status in some countries. For a review on the identification and biology of this form see the EPPO Bulletin (2016).

Vernacular names
• Deutsch: Bakterielle Tomatenwelke
Bakterienringfäule der Kartoffel
• English: tomato bacterial canker
bacterial canker of tomato
bacterial wilt of alfalfa
alfalfa bacterial wilt
potato ring rot
• Español: marchitez bacteriana
• Français: chancre bactérien
flétrissement de la pomme de terre

Clavibacter michiganensis subsp. sepedonicus (Spieckermann and Kotthoff) Davis et al. causes potato ring rot and has quarantine status in some regions. The main symptom is a discoloration of the vascular ring of the tubers which contains bacterial ooze (see illustration below). Above-ground symptoms include yellow leaf margins which become necrotic. The disease survives inside infected tubers and can be easily transmitted mechanically. Yield losses can exceed 50%.

Other subspecies are:
Clavibacter michiganensis subsp. insidiosus (McCulloch) Davis et al. - causes alfalfa bacterial wilt
Clavibacter michiganensis subsp. nebraskensis see Clavibacter nebraskensis
Clavibacter michiganensis subsp. tesselarius - causes leaf spots in wheat.

Corynebacterium michiganense