Relationships between exogenous-toxin quantity and increased biomass of transgenic Bt crops under elevated carbon dioxide

Field-OTC experiments were conducted with the goals of ascertaining if increased biomass in Bt transgenic cotton and rice grown under elevated CO2 results in diminished exogenous-Bt toxin, and assessing the effectiveness of Bt transgenes against lepidopteran pests. Bt cotton responded differently, in terms of Bt-toxin quantity, than Bt rice, and both indicated differences among developmental stages. Dramatic biomass increase significantly diluted Bt-toxin content in 45-DAS (“days after seedling”) petioles and shoots and 90-DAS Bt cotton squares, and in the 50-DAS tissues and 100-DAS leaf sheaths of Bt rice. Moreover, the dilution effect was partially responsible for decreased Bt-toxin in these tissues, but not responsible for significant decreases in Bt-toxin in 90-DAS Bt cotton leaves and bolls. Furthermore, elevated CO2 significantly affected the fitness and performance of Chilo suppressalis, and the susceptible and resistant colonies of Helicoverpa armigera, although adversely affected Bt-gene expression for the transgenic cotton and rice.