Wild sunflowers with transgene for Bt toxin produced more seeds than
normal wild sunflowers.
Cultivated sunflower (Helianthus annuus).
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
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)
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.
Ohio State University; University of Nebraska; Indiana University.
Dow AgroSciences, Pioneer Hi-Bred International, and the USDA.
Not on the market as of 2008.
Copyright 2008 The Nature