Magnitude and Strain Composition of Aspergillus flavus Soil Surface Populations in Yuma County Commerical Fields

Abstract

Aflatoxin contamination of cottonseed occurs when cotton bolls are infected by certain strains of the fungus Aspergillus flavus. The risk of aflatoxin contamination in a field is partially dependent on both the quantity of A. flavus and the toxigenicity of A. flavus strains in that field. A. flavus can be easily divided into two major subdivisions known as strain S and strain L. Strain S isolates consistently produce large amounts of aflatoxin and, therefore, the percentage of strain S isolates in the population (percent S) is one indication of the aflatoxin producing potential of the population. Strain S isolates were found in every commercial field sampled at every sampling date in Yuma County, but percent S varied greatly among fields from 4% to 93 %. Significant differences among fields located near each other suggest that locally important, but not yet identified, variables such as crop rotation histories or soil type are affecting A. flavus population magnitude and composition.