Other fungi causing brown spots

Other fungi or related organisms causing brown spots on tobacco leaves, are very rare or absent in France.
 
- Corynespora cassiicola:
This fungus causes circular spots sometimes more than 2 centimeters wide with brown concentric zones.

  In favourable conditions one can observe with a hand-lens or a microscope conidiophores bearing long, hyaline, pluricellular thick-walled conidia

- Curvularia verruculosa:
This fungus is characterised by round to oval spots, which are at first yellow then change rapidly covering the entire lamina and turn brown.
 
On the spots one can observe branched conidiophores, topped by several multicellular curved, brown conidia, with verrucolose walls (figure 1).

   - Phyllosticta nicotianae:
The spots caused by this fungus are of irregular shape (2 cm in diameter), well defined, having a clear center with brown pycnidia surrounded by darker outlines, that can be observed with a hand-lens. 
 
The pycnidia contain cylindric, one-celled conidia (figure 2).
 
  - Phytophthora nicotianae (formerly P. parasitica var. Nicotianae):
This oomycete causes large patches on tobacco leaves, which are initially wet and dark green, circular, then turn brown by necrosis. These spots can reach 8 cm in diameter.
 
In moist conditions it produces ovoid to spherical (figure 3) sporangia, spherical oospores, and numerous spherical chlamydospores are also observed in damaged tissues.
 
For further information concerning this soilborne fungus, a feared root parasite, please see the fact sheet of Phytophthora nicotianae.