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[SANET-MG] The best-laid schemes o' mice an 'men Gang aft agley



Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0409324102
Agricultural Sciences
Concurrent use of transgenic plants expressing a single and two Bacillus thuringiensis genes speeds insect adaptation to pyramided plants
( resistance management )

Jian-Zhou Zhao *, Jun Cao , Hilda L. Collins *, Sarah L. Bates *, Richard T. Roush , Elizabeth D. Earle , and Anthony M. Shelton * *Department of Entomology, Cornell University/New York State Agricultural Experiment Station, Geneva, NY 14456; Department of Plant Breeding and Genetics, Cornell University, Ithaca, NY 14853; and Statewide IPM Program, University of California, Davis, CA 95616

Transgenic plants expressing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) were grown on over 13 million ha in the United States and 22.4 million ha worldwide in 2004. Preventing or slowing the evolution of resistance by insects ("resistance management") is critical for the sustainable use of Bt crops. Plants containing two dissimilar Bt toxin genes in the same plant ("pyramided") have the potential to delay insect resistance. However, the advantage of pyramided Bt plants for resistance management may be compromised if they share similar toxins with single-gene plants that are deployed simultaneously. We tested this hypothesis using a unique model system composed of broccoli plants transformed to express different Cry toxins (Cry1Ac, Cry1C, or both) and a synthetic population of the diamondback moth (Plutella xylostella) carrying genes for resistance to Cry1Ac and Cry1C at frequencies of 0.10 and 0.34, respectively. After 24-26 generations of selection in the greenhouse, the concurrent use of one- and two-gene plants resulted in control failure of both types of Bt plants. When only two-gene plants were used in the selection, no or few insects survived on one- or two-gene Bt plants, indicating that concurrent use of transgenic plants expressing a single and two Bt genes will select for resistance to two-gene plants more rapidly than the use of two-gene plants alone. The results of this experiment agree with the predictions of a Mendelian deterministic simulation model and have important implications for the regulation and deployment of pyramided Bt plants.

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