Biological control of aflatoxin contamination using non-toxigenic Aspergillus flavus

The use of non-toxigenic isolates of Aspergillus flavus to control aflatoxin contamination of seeds has been used in a number of crops. The non-toxigenic isolate is usually applied on a substrate to the soil surface where it saprophytically colonizes organic debris and out competes the indigenous toxigenic A. flavus, presumably lowering toxigenic inoculum potential. Other work has shown that co-inoculation of non-toxigenic and toxigenic isolates in the infection court results in amelioration of aflatoxin contamination. This is considered a parasitically based mechanism. The intra-specific inhibition of aflatoxin synthesis by non-toxigenic isolates toward toxigenic isolates growing together in vitro provides a partial explanation of the co-inoculation phenomenon. Our work has shown that the intra-specific aflatoxin inhibition is nutrient and vegetative compatibility group independent, and during the first 24 hrs of toxigenic isolate growth it must physically touch or come in contact with the growing non-toxigenic isolate. Furthermore, we have shown that there is specificity in the "thigmo-down regulation" of aflatoxin synthesis. Just because an isolate inhibits one toxigenic isolate doesn't insure that it will inhibit another one. The specificity of aflatoxin inhibition allows testing of the relative importance of the two contributing mechanisms to biological control: the saprophytic/epidemiologic mechanism vs. the parasitic/thigmo-down regulation mechanism.