PARENT SESSION
Oral Session #78: Herbivory: Effects on Plants.
Presiding: C. Ivey
Thursday, August 8. 9:00 AM to 11:30 AM. Apache Meeting Room, TCC.
Effects of a Bt transgene on herbivory and fecundity in BC1 wild sunflower (Helianthus annuus).
Snow, Allison*,1, Pilson, Diana2, Rieseberg, Loren3, Paulsen, Matthew2, Pleskac, Nicholas2, Reagon, Michael*,1, Selbo, Sarena1, Wolfe, Diana3, 1 Ohio State University, Columbus, OH2 University of Nebraska, Lincoln, NE3 Indiana University, Bloomington, IN
ABSTRACT- Gene flow from transgenic crops is expected to introduce novel traits from unrelated species into sexually compatible wild relatives. Transgenes that confer resistance to insects, diseases, herbicides, or harsh growing conditions may enhance the fitness of recipient species, but the effects of this process on wild populations have not been studied. Here, we report the first empirical evidence that wild plants can benefit from a bacterial transgene under uncaged, natural conditions. Cultivated sunflower (Helianthus annuus) is known to hybridize frequently with common sunflower (also H. annuus) where they co-occur in the western and mid-western USA. We studied a crop-developed Bt transgene (Cry1Ac) in backcrossed (BC1 ) common sunflower populations that segregated for the presence or absence of the transgene. Plants were selected to be male-sterile to prevent the dispersal of Bt pollen. The transgene exhibited dominant Mendelian inheritance and was very effective in BC1 plants. Lepidopteran damage on transgenic plants was strongly reduced relative to nontransgenic control plants, while damage by several weevil and fly species was unaffected. Transgenic plants produced 55% more seeds per plant than controls at a field site in Nebraska and 14% more seeds at a site in Colorado. In a greenhouse experiment involving drought-stressed, nutrient-stressed, and control BC1 plants, the transgene had no effect on fecundity. This suggests that no inherent cost or benefit was associated with the transgene in the absence of herbivores. If Bt sunflowers are released commercially, we expect that Bt genes will spread to wild and weedy populations, kill susceptible herbivores on these plants, and increase seed production when these herbivores are common. We are conducting further studies to examine whether a strong fitness benefit due to a novel transgene could affect the abundance and/or distribution of this common agricultural weed.
KEY WORDS: transgene, herbivory, fecundity, sunflower