Crops
Thielaviopsis basicola
(black root rot of tobacco)
Thielaviopsis basicola (also called Chalara elegans) is certainly the most common and most damaging pathogen in tobacco if the varieties are not resistant. The fungus occurs both in traditional nurseries (with poor hygiene) and in floating seedbeds. It causes "black root rot" of tobacco (figures 1 and 2). This fungus is fairly easy to identify because it can be observed under a microscope or a hand lens, its brown chlamydospores are found in and on the cells of the root cortex (figure 3).
Note that this fungus spreads quickly in nurseries and that recontaminations can easily occur if you are not careful. This disease does not only cause a lot of damage in nursery, but it is also a serious threat to tobacco crop. Indeed, if the growers are not careful enough, they will infect their planting soil through the infected plants. Therefore it is extremely important not to plant contaminated seeds.
To keep guard against attacks of this fungus, please see the related protection methods.
You can consult the Thielaviopsis basicola fact sheet for more general information on this fungus.
Figure 1
Figure 2
Figure 3