Thanatephorus cucumeris
(Rhizoctonia solani)

(tobacco leaf spot)

Thanatephorus cucumeris (Rhizoctonia solani anam) causes spots on lower leaves of tobacco. These are characterised by a light brown colour and concentric rings (figures 1-4). That is why it is called in English "target spot". When the moisture content is high, a powdery felting (hymenium) may be observed on the leaves (figure 5), it produces basidiospores which are the origin of secondary aerial inoculum. This fungal disease has become recently a problem on tobacco crops, it was reported in the U.S., Canada, South Africa, Zimbabwe, Brazil and Costa Rica but not in France.
 
Note that Thanatephorus cucumeris is a basidiomycete whose imperfect form or anamorph, Rhizoctonia solani, is well-known on tobacco in France. It is rather observed on  the collar and roots, occurring both in the nursery and in the field.
 
For further information, please, see the fact sheet of Thanatephorus cucumeris (Rhizoctonia solani).