Nutrient Environments Influence Competition among Aspergillus flavus Genotypes

The population dynamics of Aspergillus flavus, shaped in part by intraspecific competition, influence the likelihood and severity of crop aflatoxin contamination. Competition for nutrients may be one factor modulating intraspecific interactions, but the influences of specific types and concentrations of nutrients on competition between genotypes of A. flavus have not been investigated. Competition between paired A. flavus isolates on agar media was affected by varying concentrations of carbon (sucrose or asparagine) and nitrogen (nitrate or asparagine). Cocultivated isolate percentages from conidia and agar-embedded mycelia were quantified by measurements of isolate-specific single-nucleotide polymorphisms with quantitative pyrosequencing. Compositions and concentrations of nutrients influenced conidiation resulting from cocultivation, but the percentages of total conidia from each competing isolate were not predicted by sporulation of isolates grown individually. Success during sporulation did not reflect the outcomes of competition during mycelial growth, and the extents to which isolate percentages from conidia and mycelia differed varied among both isolate pairs and media. Whether varying concentrations of sucrose, nitrate, or asparagine increased, decreased, or had no influence on competitive ability was isolate dependent. Different responses of A. flavus isolates to nutrient variability suggest genotypes are adapted to different nutrient environments that have the potential to influence A. flavus population structure and the epidemiology of aflatoxin contamination.