Competitive Exclusion of a Toxigenic Strain ofAspergillus flavusby an Atoxigenic Strain

Abstract

Several experiments were employed to test the role of competition in the ability of an atoxigenic strain of Aspergillus flavus to inhibit the aflatoxin contamination of developing cotton bolls. In initial tests, nitrate-nonutilizing mutants were used to follow seed infection by toxigenic and atoxigenic strains of A. flavus in coinoculated bolls. Competitive exclusion was found to contribute to the effect of the atoxigenic strain on contamination, but results suggested a second mechanism may also have been in effect. Aflatoxin contamination by the toxigenic strain was similarly inhibited by an atoxigenic strain in vivo and in liquid fermentation, and the atoxigenic strain was equally effective when applied at spore concentrations either equal to those of the toxigenic strain or one-half those of the toxigenic strain [...]