Characterization of the Aspergillus flavus population from highly aflatoxin-contaminated corn in the United States

Authors: Weaver, Mark; Callicott, Kenneth; Mehl, Hillary; Opoku, Joseph; Park, Lilly; FIELDS, KEIANA - University Of Memphis; MANDEL, JENNIFER - University Of Memphis

Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2022
Publication Date: 11/2/2022
Citation: Weaver, M.A., Callicott, K.A., Mehl, H.L., Opoku, J., Park, L.C., Fields, K., Mandel, J.R. 2022. Characterization of the Aspergillus flavus population from highly aflatoxin-contaminated corn in the United States. Toxins. 14(11). Article 755. https://doi.org/10.3390/toxins14110755.
DOI: https://doi.org/10.3390/toxins14110755

Interpretive Summary: Aflatoxin contamination of corn is a major threat to the safe food and feed. The cause of this contamination is the infection of corn with by the opportunistic pathogen Aspergillus flavus. We obtained corn samples that had been rejected due to high aflatoxin contamination and characterized the A. flavus population associated with these samples. This population was also compared to an A. flavus population from more typical corn samples to evaluate how unique the population from high aflatoxin corn was. While the two populations had substantial similarities, the striking difference was the scarcity in the high aflatoxin corn samples of a known aflatoxin biocontrol genotype that was highly abundant in the typical commercial corn sample. Both populations also had numerous isolates that were genetically similar to, but distinct from the commercial biocontrol strain, suggesting that that biocontrol strain is a representative of a very common lineage of A. flavus on corn in the US.

Technical Abstract: Aflatoxin contamination of corn is a major threat to the safe food and feed. The United States Federal Grain Inspection Service (FGIS) monitors commercial grain shipments for the presence of aflatoxin. One-hundred and fourty six Aspergillus flavus were isolated from 29 highly contaminated grain samples to characterize the visual phenotypes, aflatoxin producing potential and genotypes to explore the etiological cause of high aflatoxin contamination of US corn. Five of the isolates had reduced sensitivity (43-49% resistant) to the fungicide azoxystrobin, with the remainder all being over 50% resistant to azoxystrobin at the discrimi-nating dose of 2.5 µg / mL. Only six isolates of the highly aflatoxigenic S morphotype were found, and 48 isolates were non-aflatoxigenic. Analysis of the mating type locus revealed 45% MAT 1-1 and 55% MAT 1-2. The A. flavus population originating from the highly aflatoxin contaminated grain samples was compared to a randomly selected subset of isolates originating from commercial corn samples with typical levels of aflatoxin contaminatation (average < 50 ppb). Use of simple sequence repeat (SSR) genotyping followed by Principal Component Analysis (PCoA) revealed a similar pattern of genotypic distribution in the two populations, but greater diversity in the FGIS-derived population. The noticeable difference between the two populations was that genotypes identical to strain NRRL 21882, the active component of the aflatoxin biocon-trol product Afla-Guard™, were ten times more common in the commercial corn population of A. flavus compared to the population from the high aflatoxin corn samples. The other similarities between the two populations suggest that high aflatoxin concentrations in corn grain are generally the result of infection with common A. flavus genotypes.