Transgenic maize: unexpected differences complicate the analysis of the effects of the Bt protein on the environment

press release of May 29, 2006

Some Bt maize cultivars show differences compared to corresponding conventional cultivars that go beyond the sole production of an additional protein. Even if these differences are comparable to those observed between traditional varieties, this finding by the National Centre of Competence in Research (NCCR) Plant Survival team complicates the impact studies of Bt maize on the environment. 

The bacterium Bacillus thuringiensis (Bt) produces an insecticidal protein used against insect pests. By incorporating the bacterial gene responsible for this property into the genome of a plant, it becomes capable of protecting itself by the same means. That is the case with Bt maize, which can protect itself against a certain pest, depending on the specific Bt gene incorporated.

By comparing four Bt maize cultivars with their corresponding conventional cultivars, a team from the ETH Zurich affiliated with the NCCR Plant Survival detected other chemical differences than those attributable to the sole presence of the insecticidal protein. These differences of unknown origin influenced the development of fungi that colonise maize residues: Fusarium graminearum and Trichoderma atroviride. F. graminearum colonises both maize and wheat and produces toxins that weaken the immune system of animals and humans. T. atroviride is another fungus that could be used to control this pathogenic microorganism.

The objective of the study, that will appear in the Journal of Environmental Quality, was to compare the development of the two fungal species on both Bt and conventional maize residues. It was shown that T. atroviride was not affected by the presence of the Bt toxin. Furthermore, it seems that T. atroviride and F. graminearum are both capable of degrading the insecticidal protein produced by the transgenic plants. "Generally, Trichoderma degraded the insecticidal Bt protein more efficiently than Fusarium, clarifies Andreas Näf, who carried out this study within the framework of his PhD thesis at the ETH Zurich. An incubation period of 14 days caused a reduction of the Bt protein in maize tissue of at least 23%. Thus, application of T. atroviride on Bt maize residues to control deleterious F. graminearum could also support the degradation of the Bt protein."

"However, no definitive conclusion can be made, insists Geneviève Défago, professor at the ETH Zurich and Andreas Näf's thesis supervisor. Theoretically, the only difference between a genetically modified Bt plant and its corresponding variety should be the production of an insecticidal protein, but that is not the case in practice. Therefore, trying to show environmental effects exclusively due to the insecticidal protein produced by transgenic corn remains delicate because of the chemical differences that have been observed and are not caused by the Bt protein."


ETH Zürich
Institut für Integrative Biologie
Prof. Geneviève Défago
Tel. : +41 1 632 38 69 / 48

Andreas Näf