The Theory and Practice of Distinguishing Species of the Aspergillus Flavus Group

Summary

Sixty-two Aspergillus flavus group isolates from the SRRC and FRR culture collections were studied and identified independently by the authors. Strains were grown under standard conditions and observations recorded for a variety of morphological features at various stages of colony development. Aflatoxin production and response on a special A. flavus and A. parasiticus medium were also recorded. A discriminant analysis was performed to further study species relatedness. It was concluded that A. flavus, A. parasiticus, A. sojae, A. oryzae, and A. tamarii could be reliably separated from one another by morphological and microscopic criteria. The most salient distinguishing features were: 1) colony colour; 2) conidial size and roughening; 3) vesicle diameter; 4) conidiophore length; and 5) presence of metulae.

Aflatoxins were indicators of both A. flavus and A. parasiticus while the presence of G aflatoxins was a distinguishing feature of A. parasiticus. Columnarity of conidial heads was found to be an inconsistent character even within isolate; therefore, A. flavus var. columnaris was not distinct from the species. Isolates previously identified as A. toxicarius were identified as either A. flavus or A. parasiticus.