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June 6, 2005
Source:
Proceedings of the National
Academy of Sciences of the United States of America (PNAS)
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
ABSTRACT
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.
Source and access to full text:
http://www.pnas.org/cgi/content/abstract/0409324102v1?etoc
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