Detoxification of corn antimicrobial compounds as the basis for isolating Fusarium verticillioides and some other Fusarium species from corn

The preformed antimicrobial compounds produced by maize, 2,4-dihydroxy-7-me thoxy-2 H-1,4-benzoxazin-3-one and its desmethoxy derivative 2,4-dihydroxy- 2H-1,4-benzoxazin-3-one, are highly reactive benzoxazinoids that quickly de grade to the antimicrobials 6-methoxy-2-benzoxazolinone (MBOA) and 2-benzox azolinone (BOA), respectively. Fusarium verticillioides (= F, moniliforme) is highly tolerant to MBOA and BOA and can actively transform these compoun ds to nontoxic metabolites. Eleven of 29 Fusarium species had some level of tolerance to MBOA and BOA; the most tolerant, in decreasing order, were F. verticillioides, F, subglutinans, F. cerealis (= F, crookwellense), and F. graminearum. The difference in tolerance among species was due to their ab ility to detoxify the antimicrobials, The limited number of species having tolerance suggested the potential utility of these compounds as biologicall y active agents for inclusion within a semiselective isolation medium. By r eplacing the pentachloronitrobenzene in Nash-Snyder medium with 1.0 mg of B OA per mi, we developed a medium that resulted in superior frequencies of i solation of F. verticillioides from corn while effectively suppressing comp eting fungi. Since the BOA medium provided consistent, quantitative results with reduced in vitro and taxonomic efforts, it should prove useful for su rveys of F. verticillioides infection in field samples.