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

Aspergillus niger van Tieghem
Symptoms on grain. Colony on seed grows slowly, consisting of a compact to fairly loose
white to faintly yellow basal mycelium, which bears abundant erect and usually crowded
conidial structures, typically carbon black but sometimes deep brown-black, covering the entire
colony except for a narrow growing margin (Fig. 20). Conidial heads are typically large and
black, compact at first, spherical, or split into two or more loose to reasonably well-defined
columns, and commonly reach 700-800 μm in diameter.
(Note: Severely infected sorghum grains are discolored and shrivelled.)
Morphology. Conidiophores are smooth, hyaline or faintly brownish near the apex and up to 3
μm in length and 15-20 μrn in diameter. Apices are spherical or nearly so, up to 75 μm in
diameter but often quite small. Two series of conidia-bearing cells (supporting cells and
phialides) are produced, but in some heads only phialides are present. Supporting cells are of
varying lengths and sometimes septate, but when mature usually 20-30 μrn long. Phialides
are more uniform in length, usually 7-10 x 2-3 μm. Conidia are typically spherical at maturity,
often very rough or spiny, mostly 4—5 μm diameter, and very dark in color or with conspicuous
longitudinal striations (Fig. 21).
Quick clue. Aspergillus niger is recognized by the production of compact, greenish black,
brownish black, purplish black, or carbon black, spherical or columnar spore heads.
Importance. Seed infection can reduce germination. Production of large numbers of airdisseminated
spores can cause respiratory diseases in man and animals. Aspergillus niger is
worldwide in distribution and occurs in and upon the greatest variety of substrata including
grains, forage products, spoiled fruits and vegetables, exposed cotton textiles and fabrics,
leather, dairy products, and other protein-rich substrata (Raper and Fnnel 1973).
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