Unusual pattern of mycotoxin production in Aspergillus section Flavi

VAAMONDE, GRACIELA; PATRIARCA, ANDREA; COMERIO, RICARDO; VITALE, ROXANA; FERNÁNDEZ PINTO, VIRGINIA

Guarujá, Sao Paulo, Brasil

Simposio; X International IUPAC Symposium on Mycotoxins and Phycotoxins; 2000

IUPAC

Aspergillus section Flavi includes the three aflatoxigenic species A. flavus, A. parasiticus and A. nomius. Based on studies including a great number of isolates, a well-defined pattern of mycotoxin production for each of these species is currently accepted. A. flavus isolates may be non toxicogenic or produce type B aflatoxins (B1 and B2). Some isolates of A. flavus are also capable of producing cyclopiazonic acid (CPA), a toxic indole-tetramic acid. Simultaneous production of type B aflatoxins and CPA has been reported. A. parasiticus and A. nomius produce both B and G aflatoxins (generally B1, B2, G1 and G2) but do not produce CPA. Ability for mycotoxin production varies considerably among isolates of Aspergillus section Flavi from different substrates and different geographical areas. Characterization of toxigenic potential in native populations may be useful to develop strategies for prevention of aflatoxin contamination such as biological control. In a previous study of Aspergillus section Flavi isolates from peanuts grown in our country we found three atypical strains which have an unusual pattern of mycotoxin production. Morphologically similar to A. flavus they produce aflatoxins B1 and G1 and also CPA. Molecular work performed at University of Sydney indicates that they will probably be a new species closely related to A. flavus. In the present work, new isolates from peanuts and other substrates were screened for aflatoxins and CPA production to know the distribution of these atypical strains in our crops. A total of 67 strains from peanuts, 20 from wheat, 13 from soybeans and 4 from corn were analysed. The isolates were cultivated in Czapek-yeast extract agar (CYA) and incubated 7 days at 25ºC. Aflatoxins and CPA production was tested by the agar-plug technique. A. flavus was more frequently isolated than A. parasiticus from all substrates. Based on the combination of mycotoxins produced (AFB+/-, AFG+/- and CPA+/-) six groups of strains were established. The rate of isolates belonging to each group depended on the substrate. Only 5 isolates showed the unusual pattern of mycotoxin production. The atypical strains are not widely distributed and, up to now, they seem to be confined to peanuts. Strains with the same characteristics have been isolated only in other regions of the Southern Hemisphere (Australia and South Africa).