Intrafungal distribution of aflatoxins among conidia and sclerotia of Aspergillus flavus and Aspergillus parasiticus

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Abstract
The distribution of aflatoxins was studied among conidia and sclerotia of toxigenic strains of A. flavus and A. parasiticus cultured on Czapek agar (21 days, 28.degree. C). Total aflatoxin levels in conidia and sclerotia varied considerably within (intrafungal) and among strains. A. flavus NRRL 6554 accumulated the highest levels of aflatoxin (conidia: B1 84,000 ppb; G1, 566,000 ppb; sclerotia: B1, 135,000 ppb; G1, 968,000 ppb). Substantial aflatoxin levels in conidia could place at risk those agricultural workers exposed to dust containing large numbers of A. flavus conidia. Cellular ratios of aflatoxin B1 to aflatoxin G1 were nearly identical in conidia and sclerotia even though levels of total aflatoxins in these propagule types may have differed greatly. Aflatoxin G1 was detected in sclerotia of all A. flavus strains but in the conidia of only 1 strain. Each A. parasiticus strain accumulated aflatoxin G1 in sclerotia and conidia. These results were examined in the context of current evolutionary theory predicting an increase in the chemical defense systems of fungal sclerotia, propagules critical to the survival of these organisms.

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