A comparison of soil and corn kernel Aspergillus flavus populations: Evidence for niche specialization

Aspergillus flavus is a fungal, opportunistic, soil-borne pathogen of corn which may produce carcinogenic, acutely-toxic aflatoxins. The purpose of this study was to determine if there are two ecotypes of A. flavus: facultative parasites and saprophytes. Mature corn ears and soil samples were collected from eleven Louisiana fields in August, 2007. A. flavus was isolated from kernels (612 isolates) and soil (255 isolates). Sixteen vegetative compatibility groups (VCGs) were identified from soil isolates and six of these VCGs were found in corn isolates. Eighty-eight percent of corn isolates belonged to 2 VCGs (found in all fields) whereas only 5% of soil isolates were in the same 2 VCGs (found in 3 fields). Haplotypes were generated for a random subsample of 99 corn and 91 soil isolates from polymorphisms at 8 simple sequence repeat (SSR) loci. SSR fingerprints revealed 102 different haplotypes with 26 from corn isolates and 78 from soil isolates. One haplotype was shared between corn and soil isolates. Both VCG assemblages and SSR fingerprints differed significantly between the soil and the corn kernel populations. Differences between the populations indicate not all soil isolates are effective corn pathogens whereas some isolates have become effective at occupying the corn niche. Understanding the pathogenicity of A. flavus is important for developing atoxigenic biological control against toxigenic A. flavus and for resistance screening.