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Title: Screen of Bacillus thuringiensis toxins for transgenic rice to control Sesamia inferens and Chilo suppressalis

Author
item GAO, YULIN - China National Rice Research Institute
item HU, YANG - China National Rice Research Institute
item FU, QIANG - China National Rice Research Institute
item ZHANG, JIE - Chinese Academy Of Agricultural Sciences
item Oppert, Brenda
item LAI, FENGXIANG - China National Rice Research Institute
item ZHANG, ZHITAO - China National Rice Research Institute

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2010
Publication Date: 8/15/2010
Citation: Gao, Y., Hu, Y., Fu, Q., Zhang, J., Oppert, B.S., Lai, F., Zhang, Z. 2010. Screen of Bacillus thuringiensis toxins for transgenic rice to control Sesamia inferens and Chilo suppressalis. Journal of Invertebrate Pathology. 105(1):11-15. doi: http://dx.doi.org/10.1016/j.jip.2010.05.002.

Interpretive Summary: Transgenic rice is being developed in China to control damaging stem boring insects. The insecticidal toxins from the bacterium Bacillus thuringiensis (Bt) are effective in controlling lepidopteran (moth) pests when expressed in field crops. To identify the most effective Bt toxins for stem borer control in rice, toxins were screened for control of the pink stem borer and striped stem borer. Toxins with the highest toxicity in stem borers included Cry1Ca and a combination of Cry1Ac/Cry1Ca. Therefore, it is recommended that transgenic rice expressing these Bt toxins will be effective at controlling stem borer populations and reducing resistance development.

Technical Abstract: Transgenic rice to control stem borer damage is under development in China. To assess the potential of Bacillus thuringiensis (Bt) transgenes in stem borer control, the toxicity of five Bt protoxins (Cry1Aa, Cry1Ab, Cry1Ac, Cry1Ba and Cry1Ca) against two rice stem borers, Sesamia inferens (pink stem borer) and Chilo suppressalis (striped stem borer), was evaluated in the laboratory by feeding neonate larvae on artificial diets containing Bt protoxins. The results indicated that Cry1Ca exhibited the highest level of toxicity to both stem borers, with an LC50 of 0.24 and 0.30 micrograms/gram for C. suppressalis and S. inferens, respectively. However, S. inferens was 4-fold lower in susceptibility to Cry1Aa, and 6- and 47-fold less susceptible to Cry1Ab and Cry1Ba, respectively, compared to C. suppressalis. To evaluate interactions among Bt protoxins in stem borer larvae, toxicity assays were performed with mixtures of Cry1Aa/Cry1Ab, Cry1Aa/Cry1Ca, Cry1Ac/Cry1Ca,Cry1Ac/Cry1Ba, Cry1Ab/Cry1Ac, Cry1Ab/Cry1Ba, and Cry1Ab/Cry1Ca at 1:1 (w/w) ratios. All protoxin mixtures demonstrated significant synergistic toxicity activity against C. suppressalis, with values of 1.6- to 11-fold higher toxicity than the theoretical additive effect. Surprisingly, all but one of the Bt protoxin mixtures were antagonistic in toxicity to S. inferens. In mortality-time response experiments, S. inferens demonstrated increased tolerance to Cry1Ab and Cry1Ac compared to C. suppressalis when treated with low or high protoxin concentrations. The data indicate the utility of Cry1Ca protoxin and a Cry1Ac/Cry1Ca mixture to control both stem borer populations.