|Munkvold, Gary - IOWA STATE UNIVERSITY|
Submitted to: American Phytopathology Society Website
Publication Type: Other
Publication Acceptance Date: October 15, 1999
Publication Date: N/A
Interpretive Summary: Injuries to plants caused by insects such as the European corn borer are often the initial infection sites for a group of fungi called Fusaria. At least two species of Fusaria produce toxins called fumonisins that cause potentially fatal diseases in horses and swine and cancer in laboratory rats. Genetically-engineered (or transgenic) corn plants have a high level lof resistance to corn borer larvae. Because infection by fungi that produce fumonisins is often associated with insect damage to corn kernels, we hypothesized that genotypes of corn protected from such damage by genetic engineering might have reduced fumonisin concentrations. Our field experiments utilized several commercial transgenic hybrids and non- transgenic control hybrids. Fusarium infection of kernels was lower in transgenic hybrids compared with standard hybrids. Fumonisin concentrations were significantly lower in transgenic hybrids that were infested with European corn borer compared with non-transgenic controls. The size of the differences was sufficient to affect the toxicity of these corn kernels to horses and to human cell cultures. Considering the ubiquitous nature and carcinogenic properties of fumonisins, these results suggest that grain from transgenic maize may be safer for human and animal consumption than non-transgenic grain. Consumers interested in food safety issues, and livestock producers will benefit from this information.
Technical Abstract: Kernels of corn often contain mycotoxins produced by fungi in the genus Fusarium. Injuries to plants caused by insects such as the European corn borer, Ostrinia nubilalis, are often the initial infection sites for Fusaria. Corn borer larvae carry the fungi from plant surfaces into maize stalks and ears, and insect wounds also can be infected by airborne fungal spores. Under conditions favorable for fungal development, concentrations of mycotoxins are occasionally high enough to be harmful to livestock animals and humans. We hypothesized that maize hybrids genetically engineered with Bacillus thuringiensis genes encoding for the ë-endotoxin CryIA(b) would have reduced fumonisin concentrations compared with non- transgenic genotypes. Our field experiments utilized several commercial transgenic Bt hybrids and near-isogenic standard hybrids. Corn hybrids were either naturally infested or manually infested with O. nubilalis. Fusarium minfection of kernels was lower in Bt hybrids compared with their near- isogenic counterparts. This effect was consistent among those hybrids expressing CryIA(b) in kernels, but inconsistent in other transgenic hybrids. High levels of O. nubilalis increased infection and fumonisin concentrations in all hybrids, especially the non-transgenic hybrids. Fumonisin B1 concentrations were lower in Bt hybrids compared with their near-isogenic counterparts, but the size of this effect depended on the hybrid and whether the plants were manually infested with O. nubilalis. Statistically significant (P ó 0.05) differences in fumonisin B1 concentrations occurred only when plants were manually infested. The size of the differences was sufficient to affect the toxicity of these corn kernels to horses and to human cell cultures.