VARIABILITY AMONG ATOXIGENIC ASPERGILLUS-FLAVUS STRAINS IN ABILITY TO PREVENT AFLATOXIN CONTAMINATION AND PRODUCTION OF AFLATOXIN BIOSYNTHETIC-PATHWAY ENZYMES

Five strains of Aspergillus flavus lacking the ability to produce aflatoxins were examined in greenhouse tests for the ability to prevent a toxigenic strain from contaminating developing cottonseed with aflatoxins. All atoxigenic strains reduced contamination when inoculated into developing bells 24 h prior to the toxigenic strain. However, only one strain, AF36, was highly effective when inoculated simultaneously with the toxigenic strain. All five strains were able to inhibit aflatoxin production by the toxigenic strain in liquid fermentation. Thus, in vitro activity did not predict the ability of an atoxigenic strain to prevent contamination of developing bells. Therefore, strain selection for competitive exclusion to prevent aflatoxin contamination should include evaluation of efficacy in developing crops prior to field release. Atoxigenic strains were also characterized by the ability to convert several aflatoxin precursors into aflatoxin B-1. Four atoxigenic strains failed to convert any of the aflatoxin biosynthetic precursors to aflatoxins. However, the strain (AM6) most effective in preventing aflatoxin contamination in developing bells converted all tested precursors into aflatoxin B-1, indicating that this strain made enzymes in the aflatoxin biosynthetic pathway.