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Fusarium verticillioides produces fumonisin mycotoxins during the colonization of maize, and fumonisin B₁ (FB₁) production is necessary for manifestation of maize seedling blight disease. The objective of this study was to address FB₁ mobility and accumulation in seedlings to determine if proximal infection by F. verticillioides is necessary for FB₁ accumulation. Taking advantage of an aconidial mutant known to have limited capability for seedling infection, tissue and soil samples were analyzed to compare wild-type F. verticillioides against the mutant. Inoculation with either strain caused accumulation of FB₁ in the first and second leaves, but the mutants were unable to colonize aerial tissues. FB₁, FB₂, and FB₃ were detected in the soil and seedling roots, but only FB₁ was detected in the leaves of any treatment. These data suggest root infection by F. verticillioides is necessary for accumulation of FB₁ in leaves, but the mechanism for accumulation does not require colonization of the leaf.

In an earlier study using maize seedlings grown from kernels inoculated with Fusarium verticillioides, fumonisin B(1) (FB(1)) was preferentially accumulated in leaf tissue compared to FB(2) and FB(3). The present study tested whether maize seedlings preferentially translocate FB(1) when plants are watered with FB(1) and/or FB(2), without the fungus present. The results show that neither FB(1) nor FB(2) was translocated when administered in the watering solution, and although both FB(1) and FB(2) were taken up by the roots, the accumulation of FB(2) in roots was significantly less than expected, indicating that FB(1) was preferentially accumulated. In addition, there was clear evidence of ceramide synthase inhibition in the roots and sphingoid base and sphingoid base 1-phosphates accumulated in leaf tissue presumably due to translocation from the roots. These findings suggest that the fungus-plant interaction is necessary for FB(1) translocation in maize seedlings infected with F. verticillioides.

The fungus Fusarium verticillioides infects maize and produces fumonisins, inhibitors of ceramide synthase. Seeds of the cultivar Silver Queen were inoculated with fumonisin-producing or non-fumonisin-producing strains of F. verticillioides. Leaf lesion incidence and severity of effects on root and stalk growth were significantly correlated with fumonisin in roots and disruption of sphingolipid metabolism in roots. Uninoculated seeds grown in soil watered with solutions of fumonisin B1 exhibited above-ground symptoms indicative of F. verticillioides-induced seedling disease and dose-dependent reduction in root mass that was inversely correlated with fumonisin B1, sphingoid bases, and sphingoid base 1-phosphates in roots. There was also evidence of an adaptive response to disrupted sphingolipid metabolism in both the virulence and watering assays, suggesting induction of pathways responsible for metabolism of sphingoid base 1-phosphates after prolonged exposure. The results suggest that fumonisin, and its effects on sphingolipids, could contribute to all aspects of F. verticillioides maize seedling disease.

The fungus Fusarium verticillioides infects maize and produces fumonisins. The purpose of this study was to determine the ability of F. verticillioides to produce fumonisins in synthetic and natural soils and their biological availability to maize roots. Maize seeds were inoculated with a pathogenic strain of F. verticillioides (MRC826) and planted in synthetic and three different natural soils. There were statistically significant reductions in stalk weight and root mass and increased leaf lesions in the MRC826-treated seedlings in all soil types. Fumonisins were detected in all of the soils of seedlings grown from MRC826-inoculated seeds. The fumonisin produced in the soils was biologically available to seedlings as demonstrated by the statistically significant elevation of free sphingoid bases and sphingoid base 1-phosphates in their roots. These results indicate that F. verticillioides produced fumonisins in the autoclaved synthetic and natural soils and that the fumonisin produced is biologically available on the basis of evidence of inhibition of ceramide synthase.