Aflatoxin and cyclopiazonic acid production by Queensland isolates of Aspergillus flavus and Aspergillus parasiticus

Abstract

The production of aflatoxins (AFB1, AFB2, AFG1, AFG2) and cyclopiazonic acid (CPA) by 50 Queensland isolates of thc Aspergillusflavus-Aspergillus parasiticus group was examined for the purposes of chemotaxonomy and toxicology. lsolatcs were cultured on Czapek Dox agar at 28¦C and examined microscopically after 5, 7 and 10 days. Conidial heads were classified as either bearing phialides only or phialidcs and metulac, while conidia were classified according to degree of roughness. Isolates were also sown onto maize meal incubated at 28¦C for 28 days and assayed for aflatoxins and CPA. A. flavus types were classified as having biseriate sterigmata in 40-100% of cases and slightly to moderately rough conidia, whereas A. paraszticus types were those with 0-35% biseriate sterigmata and spikey conidia. Of the 38 isolates classed as A. flavus, 34 produced CPA (range 1-70 mg kg-1). Three isolates produced neither aflatoxins (t0.02 mg kg-1) nor CPA (< 1 mg kg-1). Seven produced CPA but no aflatoxins. The remaining 28 isolates produced AFB1 (0.02-280 mg kg-1); seven of these produced low concentrations of AFG1(0.02-0.08 mg kg-1); and only one did not produce CPA. There was no quantitative correlation between CPA and aflatoxin production by the A. fIavus isolates. Of the 12 isolates classed as A. parasiticus, none produced CPA; all produced AFB1 (4-400 mg kg-1); all produced high concentrations of AFG1 (1-400 mg kg-1). The relative prevalence of the two fungi in Queensland is discussed as a guide to the likelihood of aflatoxin and CPA contamination of different agricultural commodities.