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Genotypic Diversity of Aspergillus parasiticus in an Illinois Corn Field

Aspergillus parasiticus was isolated from direct platings of soil from a corn field near Kilbourne, Illinois. Soil contained 0.2 to 4.0 CFU of Aspergillus flavus and/or A. parasiticus per g of soil. Sixty isolates of A. parasiticus, each from a separately collected soil sample, were examined for ability to produce sclerotia and aflatoxins, and were subjected to DNA fingerprinting. PstI digests of total genomic DNA from each isolate were probed using the pAF28 repetitive sequence. Among 60 isolates analyzed, 33 (55%) distinct DNA fingerprint groups were identified (each group sharing less than 80% pAF28 band similarity), including 50 distinct genotypes (83%) with less than 100% pAF28 band similarity. A single A. parasiticus fingerprint group represented 13% of the sample population. The 83% genotypic diversity of the A. parasiticus population was equivalent to the 81% genotypic diversity recorded earlier for a population of 31 A. flavus isolates from the same field soil. Sclerotia were produced by 82% of the 50 A. parasiticus genotypes during dark incubation at 25°C. All isolates of A. parasiticus producedaflatoxin B₁B₂ and G₁G₂, whereas only 36% of the 31 A. flavus isolates from these soils produced aflatoxins.