Present in many soils and in certain substrates, responsible for damping off seedlings and root alterations (see the chapter on Root browning ), Rhizoctonia solani is mainly present in nurseries, extensive nurseries being the most affected. It is able to attack the root collar of the tomato ( Rhizoctonia basal stem canker) . On the latter, it causes lesions appearing either after planting or later on plants produced under unfavorable conditions. At first moist, brownish, sometimes reddish brown, their outline is well defined. Ultimately, these cankers may surround the base of the stem and often take on a rather dry appearance (Figures 1 and 2). Often, this damage also extends to the upper part of the root system.

It should be remembered that the partitioned, hyaline to brown mycelium characteristic of this telluric fungus is easily observable on the affected tissues, this thanks to a binocular magnifying glass (figure 3).

We were able to observe very occasionally on tomatoes the presence of the perfect form of R. solani : Thanatephorus cucumeris (basidiomycete). On this occasion, several symptoms were observed on various organs of the tomato (see the chapter on Stem alterations ), in particular on the neck of this nightshade. On the latter, we could notice a blackish wet lesion, covered in this case with a thick whitish hymenium.

R. solani and its teleomorph can also affect the stem, leaves and fruits of tomatoes.

For additional information on this fungus, you can consult the sheet Thanatephorus cucumeris (Rhizoctonia solani) fact .