A Bt TRANSGENE REDUCES HERBIVORY AND ENHANCES FECUNDITY IN WILD SUNFLOWERS

Abstract

Abstract. Gene flow from transgenic crops can introduce novel traits into related species, but the ecological importance of this process is unknown. 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 wild sunflower (H. annuus) in the western and midwestern United States. We studied a crop-developed Bacillus thuringiensis (Bt) transgene, cry1Ac, in backcrossed wild sunflower populations. Lepidopteran damage on transgenic plants was strongly reduced relative to control plants at our two study sites, while damage by several weevil and fly species was unaffected. Our results suggest that reduced herbivory caused transgenic plants to produce an average of 55% more seeds per plant relative to nontransgenic controls at the field site in Nebraska. A similar but nonsignificant trend was seen at the site in Colorado (14% more seeds per plant). In a greenhouse experiment the transgene had no effect on fecundity, suggesting that it was not associated with a fitness cost. 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.

Indirect costs of a nontarget pathogen mitigate the direct benefits of a virus-resistant transgene in wild Cucurbita

“…Most studies of the fitness of herbivore-or pathogen-resistant transgenes in crop-wild plant hybrids (and their backcross progeny) have tended to examine direct trade-offs in pairwise comparisons (e.g., with and without the target herbivore/pathogen) that lack the full host-natural enemy-community complex. Typically, these studies have found that seed production of hybrids carrying resistance to herbivores or pathogens increases in the presence of their target herbivores or pathogens (41)(42)(43)(44). However, upon escape into natural populations, resistance transgenes face a complex suite of direct and indirect costs.…”

Shared flowering phenology, insect pests, and pathogens among wild, weedy, and cultivated rice in the Mekong Delta, Vietnam: implications for transgenic rice

“…Transgenes are typically inherited as dominant traits that result from strong, constitutive gene expression, with the potential to have major effects on plant fitness (e.g., Snow et al, 2003). The evaluation of biosafety risks must consider both the probability of gene flow and its potential consequences.…”

“…The most direct method for evaluating the consequences of gene flow is to quantify the fitness effects of a transgene on hybrids between a transgenic cultivar and a wild or weedy relative under field conditions. For example, Snow et al (2003) found that a Bacillus thuringiensis (Bt) gene conferring resistance to lepidopteran herbivores increased the fecundity of hybrids between a sunflower cultivar and wild sunflower. In contrast, Burke and Rieseberg (2003) found that an oxalate oxidase transgene for white mold resistance did not confer a fecundity advantage to crop-wild hybrids in sunflower.…”

Identification and mapping of SNPs from ESTs in sunflower

“…In addition to oilseed production, sunflowers have become increasingly popular in recent years as a confectionery (snack food) and an ornamental crop. Apart from this commercial importance, the sunflowers have also recently moved to the center of the ecological and evolutionary stage (Burke and Rieseberg 2003;Rieseberg et al 2003;Snow et al 2003;Lexer et al 2004) alongside more well-studied organisms such as fruit flies (Drosophila spp. ), Darwin's finches (Geospiza spp.…”