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[SANET-MG] season decline in Bt toxin production
The paper below shows a major defect in Bt toxin production, the same
effect may also appear in maize. It seems to me this research was an
obvious direction and should have been demanded by regulators years
before the widespread use of Bt was promoted.
Season-Long Variation in Expression of Cry1Ac Gene and Efficacy of
Bacillus thuringiensis Toxin in Transgenic Cotton Against Helicoverpa
armigera (Lepidoptera: Noctuidae)
Authors: Olsen, K. M.; Daly, J. C.; Holt, H. E.; Finnegan, E. J.
Source: Journal of Economic Entomology, June 2005, vol. 98, no. 3, pp.
The insertion of genes encoding insecticidal Cry1A -endotoxins from the
bacterium Bacillus thuringiensis Berliner variety kurstaki (Bt) into
varieties of cotton (Gossypium spp.) was undertaken to assist in the
control of a range of lepidopteran pests. In Australia, where
Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren)
are major pests, the level of control is useful, but not complete,
because efficacy declines as the crop matures. Fluctuations in the
efficacy of Bt cotton, to the extent that some insects survive, provide
opportunities for H. armigera to develop resistance to the Bt toxin.
Therefore, variations in the efficacy of Bt cotton need to be understood
if we are to plan rational resistance management strategies to retard
the rate of the development of resistance. We measured the changes in
efficacy associated with plant development over the growing season, in
the field and glasshouse. In addition, the levels of Cry1Ac protein
toxin and cry1Ac RNA were determined. In this first demonstration of the
relationship between these three factors, we found that the
developmental decline in bioefficacy in field-grown plants was
associated with reduced cry1Ac transcript levels and Bt toxin levels in
postsquaring cotton. In addition, changes in plant chemistry associated
with the maturation of the cotton plant were observed to contribute to
changes in the efficacy of Bt toxin. Results from the field and
glasshouse suggested that variations in efficacy within the growing
season and between seasons also may be influenced by environmental factors.
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