Background/Question
Since pollen flow or seed dispersal usually lead to the presence of transgenic plants in the nature, the coexistence of transgenic crops and their wild relatives is an environmental concern. In this study we tested the hypothesis that competition and herbivory selective pressures can change the rate of transgene flow from transgenic crops to wild species and increase the potential of transgene escape risk and persistence outside of cultivation.
Methods
We conducted filed experiments using cages with nets, and cultivated Bt-transgenic Brassica napus (Bt OSR) and wild mustard (B. juncea) in pure or mixed stands. Lepidopteran herbivores (Plutella xylostella), stimulating low herbivory, were applied and rates of transgene flow and reproductive organs were measured.
Results
Bt OSR produced more ovules and pollen than wild mustard, but their ratios of pollen and ovule (P/O) were not significantly different. Low herbivory had no effects on fitness parameters of Bt OSR and wild mustard, and also on the transgene flow rate. All Bt progenies of wild mustard plants were from mixed cages, with a gene flow rate of 0.66%. Wild mustard produced less pollen and more ovule and therefore lower P/O ratio in mixed stands than in pure stands. A lower P/O ratio indicates a shift in sex allocation toward greater female investment, which indicates a higher potential gene flow rate received pollen from transgenic plants.
Conclusions
The findings of this study indicate that the presence of transgenic plants in wild populations may further increase the potential transgene flow through altering reproductive traits of wild species.