Field Efficacy and Seasonal Expression Profiles for Terminal Leaves of Single and Double &lt;I&gt;Bacillus thuringiensis&lt;/I&gt; Toxin Cotton Genotypes

Adamczyk, John J.; Adams, L. C.; Hardee, D. D.

doi:10.1603/0022-0493-94.6.1589

Cited by 125 publications

(67 citation statements)

References 8 publications

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“…However, unlike our results showing similar seasonal declines of about threefold in Cry1Ac and Cry2Ab in DP 164 B2RF, previous studies with other cultivars found that the seasonal decline in toxin concentration was generally less for Cry2Ab (35)(36)(37) than Cry1Ac (38)(39)(40)(41)(42). In any case, seasonal declines in the concentration of Bt toxins could be an important factor affecting redundant killing because there is extensive variation among cotton cultivars in patterns of production of Bt toxins (43).…”

Section: Discussioncontrasting

confidence: 98%

Potential shortfall of pyramided transgenic cotton for insect resistance management

Brévault

Heuberger

Zhang

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

154

222

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To delay evolution of pest resistance to transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt), the "pyramid" strategy uses plants that produce two or more toxins that kill the same pest. In the United States, this strategy has been adopted widely, with two-toxin Bt cotton replacing one-toxin Bt cotton. Although two-toxin plants are likely to be more durable than one-toxin plants, the extent of this advantage depends on several conditions. One key assumption favoring success of two-toxin plants is that they kill insects selected for resistance to one toxin, which is called "redundant killing." Here we tested this assumption for a major pest, Helicoverpa zea, on transgenic cotton producing Bt toxins Cry1Ac and Cry2Ab. Selection with Cry1Ac increased survival on two-toxin cotton, which contradicts the assumption. The concentration of Cry1Ac and Cry2Ab declined during the growing season, which would tend to exacerbate this problem. Furthermore, analysis of results from 21 selection experiments with eight species of lepidopteran pests indicates that some cross-resistance typically occurs between Cry1A and Cry2A toxins. Incorporation of empirical data into simulation models shows that the observed deviations from ideal conditions could greatly reduce the benefits of the pyramid strategy for pests like H. zea, which have inherently low susceptibility to Bt toxins and have been exposed extensively to one of the toxins in the pyramid before two-toxin plants are adopted. For such pests, the pyramid strategy could be improved by incorporating empirical data on deviations from ideal assumptions about redundant killing and cross-resistance. (Résumé d'auteur

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Section: Discussioncontrasting

confidence: 98%

Potential shortfall of pyramided transgenic cotton for insect resistance management

Brévault

Heuberger

Zhang

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

154

222

View full text Add to dashboard Cite

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“…This was a qualitative ELISA analysis. ELISA is an economical method for detecting Cry1Ac in cotton and has been used for this purpose in many studies (Abel and Adamczyk, 2004;Adamczyk et al, 2001;Anklam et al, 2002;Kranthi et al, 2005;Sims and Berberich, 1996).…”

Section: Cry1ac In Cotton Bollsmentioning

confidence: 99%

Outcrossed cottonseed and adventitiousBtplants in Arizona refuges

Heuberger

Yafuso

DeGrandi-Hoffman

et al. 2008

Environ. Biosafety Res.

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Outcrossing of non-Bt cotton (Gossypium hirsutum (L.)) in refuges by transgenic Bt cultivars could reduce the efficacy of refuges for delaying resistance in seed-feeding pests. Based on reports that outcrossing decreased as distance from Bt cotton increased in small-scale studies, we hypothesized that increasing refuge width or distance from Bt fields would reduce outcrossing. In a large-scale study in Arizona, we quantified Bt seed in refuges of experimental and commercial fields, comparing outcrossing between in-field (narrow) and external (wide) refuges and among rows of refuges at various distances from Bt fields. Some refuges, including those in tightly controlled experimental plots, contained up to 8% adventitious Bt plants. Some, but not all, Bt plants likely resulted from Bt seed in the non-Bt seed bags. We did not detect a difference in outcrossing between infield and external refuges. However, statistical power was low because outcrossing was low (< 0.4% of seeds) in both treatments. Higher outcrossing levels (≤ 4.6% of seeds) were observed in the studies measuring outcrossing at various distances from Bt fields, yet outcrossing did not decrease as the distance from Bt fields increased. We hypothesize that Bt plants in refuges cross-pollinated surrounding non-Bt plants, overshadowing the expected association between distance from Bt fields and outcrossing.

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“…Consequently, Cry1Ac and Cry2A are good candidates for gene stacking in Bt cotton to control H. virescens; since they do not share binding sites in H. virescens, they share low sequence homology and have distinct modes of action (7,35). Furthermore, this combination of toxins broadens the toxicity spectra of the cultivars, because Cry2A toxins are active against some lepidopteran pests that are unaffected by Cry1Ac (1,39,43). Bt cotton plants expressing both Cry1Ac and Cry2Ab toxins will be the first commercial plants developed based on the gene stacking strategy.…”

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confidence: 99%

Dual Resistance to Bacillus thuringiensis Cry1Ac and Cry2Aa Toxins in Heliothis virescens Suggests Multiple Mechanisms of Resistance

Jurat-Fuentes¹,

Adang

2003

Appl Environ Microbiol

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One strategy for delaying evolution of resistance to Bacillus thuringiensis crystal (Cry) endotoxins is the production of multiple Cry toxins in each transgenic plant (gene stacking). This strategy relies upon the assumption that simultaneous evolution of resistance to toxins that have different modes of action will be difficult for insect pests. In B. thuringiensis-transgenic (Bt) cotton, production of both Cry1Ac and Cry2Ab has been proposed to delay resistance of Heliothis virescens (tobacco budworm). After previous laboratory selection with Cry1Ac, H. virescens strains CXC and KCBhyb developed high levels of cross-resistance not only to toxins similar to Cry1Ac but also to Cry2Aa. We studied the role of toxin binding alteration in resistance and cross-resistance with the CXC and KCBhyb strains. In toxin binding experiments, Cry1A and Cry2Aa toxins bound to brush border membrane vesicles from CXC, but binding of Cry1Aa was reduced for the KCBhyb strain compared to susceptible insects. Since Cry1Aa and Cry2Aa do not share binding proteins in H. virescens, our results suggest occurrence of at least two mechanisms of resistance in KCBhyb insects, one of them related to reduction of Cry1Aa toxin binding. Cry1Ac bound irreversibly to brush border membrane vesicles (BBMV) from YDK, CXC, and KCBhyb larvae, suggesting that Cry1Ac insertion was unaffected. These results highlight the genetic potential of H. virescens to become resistant to distinct Cry toxins simultaneously and may question the effectiveness of gene stacking in delaying evolution of resistance.

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Field Efficacy and Seasonal Expression Profiles for Terminal Leaves of Single and Double <I>Bacillus thuringiensis</I> Toxin Cotton Genotypes

Cited by 125 publications

References 8 publications

Potential shortfall of pyramided transgenic cotton for insect resistance management

Potential shortfall of pyramided transgenic cotton for insect resistance management

Outcrossed cottonseed and adventitiousBtplants in Arizona refuges

Dual Resistance to Bacillus thuringiensis Cry1Ac and Cry2Aa Toxins in Heliothis virescens Suggests Multiple Mechanisms of Resistance

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