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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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