Technical Abstract: The interaction between maize and Gibberella fujikuroi mating population A (MP-A; =Fusarium moniliforme) involves the plant's defensive compounds DIMBOA and DIBOA. These preformed compounds and their derivatives have wide-ranging antimicrobial activity, yet MP-A is very tolerant because of its ability to detoxify the compounds. A screen of many Fusarium species showed that MP-A had the greatest tolerance. Of the >50 strains of MP-A screened, only one was found to be sensitive to the compounds. Subsequent genetic analyses assessing segregation of tolerant and sensitive progeny indicated that two loci, Fdb1 and Fdb2, are involved in detoxification. In vitro physiological complementation assays resulted in detoxification of the antimicrobial BOA and have suggested an unknown intermediate compound is produced. Cloning of Fdb1+ by genetic complementation is underway. Cloning and targeted disruption of the native Fdb1+ allele in a detoxifying strain of MP-A will allow for stringent testing of hypotheses regarding the impact of antimicrobial detoxification on fungal virulence and/or fitness for endophytic growth.