Description of the fungus  

• The conidiophores of Alternaria spp. are often dark, simple or branched, more or less twisted.
• Of conidia are produced in their chain terminus. These multicellular conidia (= dictyospores) are initially ovoid then end up being prolonged by a beak, then taking the shape of a club and gradually a brown tint (figure 1). The transverse and longitudinal partitions of these conidia constitute a characteristic characteristic of the genus Alternaria . Assembled in chains of varying length (figure 2), they have an irregular shape and variable dimensions (20-80 x 9-18 µm). Their apical bill, well differentiated, does not exceed 1/3 of the total length of the conidium.
• Appearance of colonies on malt-agar medium : they have a heterogeneous appearance, sterile white areas made up of aerial hyphae alternating with darker, grazing areas in which melanized conidia are produced. Alternaria alternata grows rapidly on this medium to initially give colonies in gray tones, which turn brown with age.