Fusarium moniliforme Sheldon is a nonobligate parasite of maize that produces several mycotoxins. This fungus causes systemic infections of maize kernels, which then serve as dissemination vehicles and inoculum sources. Infected plants may or may not show disease symptoms. Symptomless infection was studied in maize plants and was compared with plants that eventually showed symptoms of seedling disease. Three isolates of F. moniliforme, a hygromycin-resistant mutant of two of these isolates, and Fusarium fujikuroi were used to infect surface and internally sterilized maize kernels, and symptomatic and symptomless infections were observed for 8 weeks. The results indicated that in symptomless infected plants, hyphae were intercellular only and distributed throughout the plant, whereas in plants showing disease symptoms, the fungus was both intercellular and intracellular. Symptomless plants remained symptomless throughout the observation period, and at the ultrastructural level there was no evidence of an antagonistic relationship. This indicates that the symptomless state persists beyond the seedling stage and could contribute, without visual signs, to the total mycotoxin contaminants of maize both before and during kernel development. Keywords: Gibberella fujikuroi, endophyte, toxic fungus, maize, fusarium toxins, corn disease.

The preformed antimicrobial compounds produced by maize, 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one and its desmethoxy derivative 2,4-dihydroxy-2H-1,4-benzoxazin-3-one, are highly reactive benzoxazinoids that quickly degrade to the antimicrobials 6-methoxy-2-benzoxazolinone (MBOA) and 2-benzoxazolinone (BOA), respectively. Fusarium verticillioides ‫؍(‬ F. moniliforme) is highly tolerant to MBOA and BOA and can actively transform these compounds 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 ability to detoxify the antimicrobials. The limited number of species having tolerance suggested the potential utility of these compounds as biologically active agents for inclusion within a semiselective isolation medium. By replacing the pentachloronitrobenzene in Nash-Snyder medium with 1.0 mg of BOA per ml, we developed a medium that resulted in superior frequencies of isolation of F. verticillioides from corn while effectively suppressing competing fungi. Since the BOA medium provided consistent, quantitative results with reduced in vitro and taxonomic efforts, it should prove useful for surveys of F. verticillioides infection in field samples.

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Fumonisins are potent inhibitors of sphingolipid biosynthesis produced by several Fusarium species. Consumption of corn or corn products infected with F. moniliforme, or high levels of fumonisins, is associated with several animal diseases. In a 4-wk feeding study, the concentration of fumonisin B1 that caused nephrotoxicity in Sprague-Dawley rats was much less than that required to cause hepatotoxicity. This retrospective study shows a close correlation between the extent and severity of ultrastructural lesions and the degree of disruption of sphingolipid metabolism. The kidney was more sensitive to fumonisin B1-induced disruption of sphingolipid metabolism than liver with significant elevation of free sphingosine, free sphinganine, and the free sphinganine:free sphingosine ratio in rats fed 15, 50 and 150 micrograms/g fumonisin B1. Accumulation of free sphinganine and elevation of the free sphinganine:free sphingosine ratio in urine closely reflected the changes that occurred in kidney. The accumulated sphinganine and elevation of the free sphinganine:free sphingosine ratio was associated with accumulation of cells in urine. Thus, urine rather than serum is the fluid of choice for detecting elevated free sphingoid bases generated as a consequence of fumonisin-induced kidney damage.

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