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

Alternaria longissima Deighton & MacGarvie
Symptoms on grain. Colony on grain is brown to blackish brown (Fig. 12).
Morphology. Mycelium is partly superficial and partly immersed. Conidiophores are erect or
ascending, simple or occasionally branched, straight or slightly flexuous, sometimes geniculate,
somewhat swollen at the apex, septate, pale to mid-pale brown, smooth below, verruculose at
and sometimes below the apex, 150 μm long, 3-5 μm thick, with one to several conidial scars.
Conidia are solitary or catenulate, extremely variable in shape and size, pale straw colored to
brown. They are usually very long (up to 500 μm), Cercospora-like, obclavate or with a basal
sub-cylindric portion of few to several cells and a very long, narrow septate beak (Fig. 13). They
have 5-40 transverse septa. Conidia are 4-17 μm thick in the broadest part and about 2.5 μm
thick at the apex. Shorter conidia, variable in shape and often with a few longitudinal or oblique
septa, are also formed. Conidia are thin-walled, smooth except around the base where they are
often verruculose. Dark brown, multicellular, muriform chlamydospores 16-42 x 16-34 μm
sometimes occur, both on natural substrata and in culture.
Quick clue. Very long, Cercospora-like conidium is a distinct feature of A. longissima.
Importance. The fungus was previously reported on sorghum along with method(s) to kill the
fungus adhering to the grains for safe use of grains for consumption (Navi et al. 1997).
Metabolites isolated from A. longissima include tenuazonic acid, cellulase, and
polygalacturonase (von Ramm and Lucas 1963; Mikami et al. 1971).
Figure 12
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