Abstract
Gene flow from transgenic crops allows novel traits to spread to sexually compatible weeds. Traits such as resistance to insects may enhance the fitness of weeds, but few studies have tested for these effects under natural field conditions. We created F2 and F3 crop–weed hybrid lineages of genetically engineered rice (Oryza sativa) using lines with two transgene constructs, cowpea trypsin inhibitor (CpTI) and a Bt transgene linked to CpTI (Bt/CpTI). Experiments conducted in Fuzhou, China, demonstrated that CpTI alone did not significantly affect fecundity, although it reduced herbivory. In contrast, under certain conditions, Bt/CpTI conferred up to 79% less insect damage and 47% greater fecundity relative to nontransgenic controls, and a 44% increase in fecundity relative to the weedy parent. A small fitness cost was detected in F3 progeny with Bt/CpTI when grown under low insect pressure and direct competition with transgene-negative controls. We conclude that Bt/CpTI transgenes may introgress into co-occurring weedy rice populations and contribute to greater seed production when target insects are abundant. However, the net fitness benefits that are associated with Bt/CpTI could be ephemeral if insect pressure is lacking, for example, because of widespread planting of Bt cultivars that suppress target insect populations.
Highlights
The environmental release of transgenic crops has generated considerable debate about the ecological and evolutionary consequences of adopting these crops
This study confirms that insect-resistance transgenes from cultivated rice are effective when transferred to weedy rice and can increase fecundity of weedy rice when target insects are present
Results from the F2 and F3 hybrid generations were generally consistent, demonstrating that the Bt/cowpea trypsin inhibitor (CpTI) transgene can result in lower insect damage and greater seed production under natural field conditions, with no effects on survival
Summary
The environmental release of transgenic crops has generated considerable debate about the ecological and evolutionary consequences of adopting these crops. A major biosafety concern relates to unwanted effects because of transgene flow from genetically engineered (GE) crops to their wild or weedy relatives (Ellstrand 2003; Snow et al 2005). Novel transgenic traits that enhance fitness are expected to introgress into recipient populations, whereas traits that are associated with fitness costs may eventually be lost (Jenczewski et al 2003). Studies of such fitness consequences under natural biotic and abiotic conditions are uncommon, in part because so few of the currently grown transgenic crops can hybridize with feral, weedy, or wild relatives (exceptions include canola and squash). The number and diversity of transgenic crops, including the introduction of relatively undomesticated biofuel crops, is expected to increase dramatically in the coming decade (Gressel 2008)
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