Fusarium oxysporum f. sp. nicotianae

(Fusarium wilt)

Fusarium oxysporum f. sp. nicotianae (Fusarium wilt), is a vascular pathogen  rather specific to tobacco, it is not currently present in France. As the bacterium Ralstonia solanacearum, it is most prevalent in many tropical and subtropical countries, especially in the Americas and Asia. The damage caused by this fungus can be significant.
 
It causes foliar symptoms which are very similar to those induced by Verticillium dalhiae (figures 1 and 2). However, unlike Verticillium wilt, in the case of Fusarium wilt, stem vessels have an even dark to chocolate brown color (figure 3). The cortex of the stem can also be affected (figure 4). Fusarium oxysporum f. sp. nicotianae develops in the xylem where it obstructs the vessels by gums which contribute to plant wilting by disrupting the sap flow.
 
Note that this fungus is characterised by short, branched conidiophores, with  unicellular microconidia, multicellular macroconidia and chlamydospores. For further information we recommand you to consult the fact sheet of Fusarium oxysporum f. sp. nicotianae