A Pictorial Guide for the Identification of Mold ... - OAR@ICRISAT

Alternaria alternata (Fr.) Keissler
Symptoms on grain. The fungus produces woolly or powdery chains of dark brown conidia
of variable lengths and shapes. The color of the colony is usually extremely variable between
olive green to dark brown (Fig. 6a, b).
Morphology. The mycelium may be either sparse or abundant and variable in color, usually
light olive green to brown. Hyphae are dark brown, thick, septate, and branched.
Conidiophores are simple, erect, 40-50 μm long, 2-6 μm thick, and often clustered.
Conidiophores produce dark pigmented conidia in an acropetal succession of simple or
branched chains. These chains normally branch at the beak of a spore, or sometimes from
the short lateral projection of the beak. Conidia have transverse and oblique septa, measure
10-18 x 20-65 μm, and are ovoid to obovoid, obclavate, obpyriform, ellipsoidal, uniform,
with an elongated terminal cell (Fig. 7). Conidia often have a short conical or cylindrical beak
which is about one third the length of the conidium, and measure 2-5 x 10-20 μm. Surface
walls are either smooth or verrucose and pale to mid-golden brown.
Quick clue. Chains of conidia are produced at the beak of a spore, or sometimes from the
short lateral projection of the beak.
Importance. The fungus is distributed worldwide and is usually seedborne. It causes leaf
spot on several hosts and blight of pigeonpea (Cajanus cajan (L.) Millsp.), chickpea (Cicer
arietinum L), and groundnut (Arachis hypogaea L ) . Several metabolites and toxins have
been isolated from A. alternata: tentoxin (Templeton 1972), AF-toxins I and II (Maekawa et al.
1984), alkaloids (Rizk et al. 1985), alternariol (Logrieco et al. 1990), and mannitol
(Combe et al. 1970).
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