Sclerotinia sclerotiorum

(Sclerotinia leaf spot, Sclerotinia stem rot)

Sclerotinia leaf spot is a common disease in France. It mainly infects the stem and leaves of tobacco. 
 
The main symptoms caused by Sclerotinia sclerotiorum, on mature plants, are light brown to beige lesions located on leaf midribs (figures 1 and 2). Stems cankers (figure 3) initiating from the petiole of senescent leaves are also observed.

Sclerotinia sclerotiorum is easy to identify. It is characterised by a white mycelium and large black sclerotia. To confirm Sclerotinia diagnosis you may induce the development of fungal structures by placing some samples in an airtight container (a plastic bag) containing a damp paper towel. This will provide the required humidity for the formation of these structures.
 
Apothecia (figure 4), the sexual (teleomorph), form of the fungus sometimes occur in the field.
  
   
For further information on this fungus, please see the fact sheet for Sclerotinia sclerotiorum.