Poster: Biotech Risk Assessment
Abs #
902: Competition, growth, and nitrogen use efficiency of transgenic weedy Brassica rapa
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Presenter: |
Stewart, Jr., C. Neal , nealstewart@utk.edu |
Authors | Stewart, Jr., C. Neal (A) Halfhill, Matthew D. (A) (B) Rufty, Thomas W. (B) Raymer, Paul L. (C) Weissinger, Arthur K. (B) Warwick, Suzanne I. (D) | | Affiliations: |
(A): University of Tennessee
(B): N.C. State University
(C): University of Georgia
(D): Agriculture and Agri-food Canada
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| Web Site: | http://psls.ag.utk.edu/stewart.htm | |
Much has been written about the suspected weed enhancement conferred by the crop-borne introgression of transgenes such as one coding for insect resistance and the creation of “superweeds”. We have experimentally examined the superweed scenario in backcrossed introgressed crop × weed populations. The transgenic crop used was Brassica napus cv ’Westar’ harboring insect resistance Bacillus thuringiensis (Bt) cry1Ac and a green fluorescent protein (gfp) transgenes. These transgenes were introgressed into BC2F2 Bulk weedy Brassica rapa populations, with F1, BC1F1, BC2F1 populations and a BC2F2 nontransgenic population created en route. Experiments using continuous flow hydroponics showed that under high N, wild type B. rapa outperformed B. napus and transgenic hybrid populations with higher growth rates and N accumulation. There were no differences among plant types in experiments where growth was limited by low N availability. BC2F2 Bulk transgenic weedy Brassica rapa populations were competed against wheat in the field to test whether transgene introgression would enhance their competitiveness. Wheat had decreased yield and biomass when grown in the presence of any Brassica competitor, but fared best when competed against BC2F2 Bulk transgenic weedy B. rapa populations. The latter decreased wheat yield by 25%, while nontransgenic B. rapa, nontransgenic BC2F2 and transgenic B. napus reduced wheat yield by 47%; a significant difference. These results have led us to pose a genetic load hypothesis: selection for a transgene in introgressed weeds will be accompanied by crop genes in linkage disequilibrium, decreasing the competitive nature of an erstwhile highly fit weed by the genetic pollution of crop genes.
