Differentiation of Aspergillus flavus from A. parasiticus and other closely related species

More than 150 isolates of Aspergillus flavus, A. oryzae, A. parasiticus, A. sojae and A. tamarii from collections around the world were examined independently in two laboratories as unknowns, and data assessed to evaluate a wide range of morphological characters for suitability as taxonomic criteria. Mycotoxin production was also assessed. It was concluded that conidial wall texture was the most effective criterion for distinguishing A. flavus and A. parasiticus. A. flavus has a broad interface with VA. oryzae; therefore, a combination of characters was necessary to separate these two species. Mycotoxin production correlated well with morphological speciation. Only A. flavus and A. parasiticus isolates produced B aflatoxins. Very few A. flavus isolates produced G aflatoxins whereas almost all A. parasiticus isolates did. The A. parasiticus isolates never produced cyclopiazonic acid, but some isolates of A. flavus, A. tamarii and A. oryzae did.