Aspergillus flavus Populations in Matrices of the Corn Agroecosystem

Infection of corn by the pathogen Aspergillus flavus can result in the contamination of the grain with aflatoxin, a potent, regulated mycotoxin. A. flavus has high genetic diversity, even within a single field, but it is unknown if the population is homogeneous among the different matrices of the corn agroecosystem or whether there are discernable subpopulations. We collected isolates of A. flavus from two sites for 2 years from soil, grain, corn silks, and Helicoverpa zea moths and larvae. This collection of more than 1,000 isolates of A. flavus were screened and characterized based on aflatoxigenic potential, sclerotial morphotype, and 17 simple sequence repeat (SSR) markers. The collection from the Corpus Christi, Texas, study site had a higher frequency of aflatoxigenic isolates than the collection from Stoneville, Mississippi. The genotype of a commercially available biocontrol isolate of A. flavus was present at both study sites but was five times more abundant at Stoneville, Mississippi, than at Corpus Christi, Texas. SSR-based population genetics indicated that the A. flavus populations collected from various matrices were not differentiated and that there appeared to be significant gene flow among the populations within each site.