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Wild sunflowers with transgene for Bt toxin produced more seeds than normal wild sunflowers.

Manipulated Organism: Cultivated sunflower (Helianthus annuus).

Inserted Transgene: crylAc gene derived from Bacillus thuringiensis ("Bt"). The gene crylAc is for production of the protein crylAc, which is fatal to many larvae of lepidoptera (moth) species. The gene was fused to the cauliflower mosaic virus (CaMV-35S) promoter so that the insecticide would be produced in all parts of the plant. A transgenic line of Bt sunflowers was developed by Dow AgroSciences and Pioneer Hi-Bred for potential commercialization as an insect-resistant crop.

Goal of This Study: Environmental risk assessment. Since cultivated sunflowers frequently hybridize with wild sunflowers in the western and midwestern United States, this study sought to assess the likelihood of genetically modified hybrids spreading as weeds in agricultural areas or otherwise disturbing population dynamics of wild sunflowers in nonagricultural areas. To mimic the escape of the Bt transgene into the wild, the researchers crossed Bt cultivated sunflowers with wild sunflowers to obtain transgenic wild sunflowers that were Bt-resistant. They planted these hybrids along with unmanipulated wild sunflowers in field plots in Nebraska and Colorado.

Results of This Study: The transgenic plants produced "significantly more inflorescences, more inflorescences that produced mature seeds and more viable seeds per plant than nontransgenic controls" (p. 284). In greenhouse experiments, where the microenvironment was varied to mimic environmental stress conditions, but insect pests were excluded, there was no difference in seed or inflorescence production between Bt hybrids and nontransgenic plants. "This indicates that the transgene was not associated with an inherent fitness cost or benefit. . . . Our results suggest that the fecundity advantage of transgenic plants in the field was due to protection from lepidopteran herbivores" (p. 284). The authors conclude:
If Bt sunflowers are released commercially, we expect that Bt genes will spread to wild and weedy populations, limit damage from susceptible herbivores on these plants, and increase seed production when these herbivores are common. (p.279)

Our study is the first to demonstrate that a transgene derived from a crop has the potential to increase the fitness of wild plants, and thus increase in frequency in wild populations. . . . A crylAc gene that becomes common in wild sunflower populations will clearly have negative effects on the suite of native lepidopteran herbivores that use wild sunflowers as their primary host plant. (p.285)

Source: Snow A. A., D. Pilson, L. H. Rieseberg et al. (2003). "A Bt Transgene Reduces Herbivory and Enhances Fecundity in Wild Sunflowers," Ecological Applications vol. 13(2), pp. 279-86.

Author Affiliations: Ohio State University; University of Nebraska; Indiana University.

Funding: Dow AgroSciences, Pioneer Hi-Bred International, and the USDA.

Product Status: Not on the market as of 2008.

Copyright 2008 The Nature Institute.

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