Thanatephorus cucumeris

(damping-off, shore shin, target spot)

Thanatephorus cucumeris (Rhizoctonia solani) is especially known to cause "damping-off” (figure 1), lesions on the collar (" sore shin ") (figure 2) and, in some countries, leaf spots ("target spot") (figure 3). Its pathogenicity on the roots of tobacco grown in field is not well known and seems somewhat underestimated.
 
One can observe characteristic brown mycelium (figure 4) on rotten, superficially suberised "corky" roots (figures 5 and 6) of slowly growing tobacco. Is it simply a biological indicator of root systems having suffered from agro-climatic stress? Is it a fungus indicator of a “tired” soil” having parasitic potential by itself or in combination with other pests or under the influence of non-parasitic diseases? It is difficult to answer all these questions. It is certain that a number of strains are pathogenic to all the organs on which the fungus has been described and inoculated. In some cases, one can hardly imagine that the high concentration of mycelium on roots, associated with a significant pathogenicity, does not have any impact on them.

Figure 4	Figure 5	Figure 6

  For further information see the fact sheet of Thanatephorus cucumeris (Rhizoctonia solani)