Aspergillus niger is one of the most common and easily identifiable species of the genus Aspergillus, with its white to yellow mat later bearing black conidia. On Czapek agar, colonies consist of a compact white or yellow basal felt covered by a dense layer of dark-brown to black conidial heads. Conidial heads are large (up to 3 mm x 15-20 um in diameter), globose, dark brown, becoming radiate and tending to split into several loose columns with age. Conidiophores are smooth-walled, hyaline or turning dark towards the vesicle. Conidial heads are biseriate with the phialides borne on brown, often septate metulae. Conidia are globose to subglobose (3.5-5.0 um in diameter), dark brown to black and rough-walled.
Cultures of aspergillus niger show relatively slow (2.5-3.5 mm per day) radial extension at room temperature (24-26°C) on weak media such as Czapek's agar, but at higher temperatures (30-35°C) and/or richer media, growth proceeds more rapidly.
Propagules of aspergillus niger (most probably conidia) are common in the soil and air mycoflora of regions with hot climates. Thus emerging seedlings may potentially be affected by soilborne aspergillus niger, and the growing crop by airborne aspergillus niger. Contaminated seed may also be a major source of inoculum.
The following test is performed to determine the presence of aspergillus niger:
1. Seed is either untreated or pretreated with 2% NaOCl.
2. Incubate on a blotter for 24 h at 20°C, 24 h at -20°C, and 7 days at 20°C and 12 h dark/12 h NUV light.
The fungus may develop on the ears of maize, the sooty mould eventually covering the whole ear. Subsequent seed germination is reduced and seeds are discolored and shriveled. In soybeans a mixture of species including aspergillus niger which can cause discoloration, caking, mustiness and heating.
This is the third most common species associated with invasive pulmonary aspergillosis. Aspergillus niger produces a range of extracellular enzymes and is used commercially in the fermentation industries. It produces an antifungal peptide that suppresses growth of a range of fungi and siderophores.
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