Issue Environ. Biosafety Res. Volume 1, Number 1, October 2002 Page(s) 19 - 28 DOI 10.1051/ebr:2002002

Environ. Biosafety Res. 1 (2002) 19-28
DOI: 10.1051/ebr:2002002

Bt-transgenic oilseed rape hybridization with its weedy relative, Brassica rapa

Matthew D. Halfhill¹, Reginald J. Millwood¹, Paul L. Raymer² and C. Neal Stewart Jr.<sup>3

1</sup>  University of North Carolina at Greensboro, Department of Biology, 312 Eberhart Bldg. Greensboro, NC 27402, USA
²  University of Georgia, Georgia Experiment Station, Griffin, GA 20223, USA
³  Dept. of Plant Science and Landscape Systems, University of Tennessee, Knoxville, TN 37996, USA

Abstract
The movement of transgenes from crops to weeds and the resulting consequences are concerns of modern agriculture. The possible generation of "superweeds" from the escape of fitness-enhancing transgenes into wild populations is a risk that is often discussed, but rarely studied. Oilseed rape, Brassica napus (L.), is a crop with sexually compatible weedy relatives, such as birdseed rape (Brassica rapa (L.)). Hybridization of this crop with weedy relatives is an extant risk and an excellent interspecific gene flow model system. In laboratory crosses, T ₃ lines of seven independent transformation events of Bacillus thuringiensis (Bt) oilseed rape were hybridized with two weedy accessions of B. rapa. Transgenic hybrids were generated from six of these oilseed rape lines, and the hybrids exhibited an intermediate morphology between the parental species. The Bt transgene was present in the hybrids, and the protein was synthesized at similar levels to the corresponding independent oilseed rape lines. Insect bioassays were performed and confirmed that the hybrid material was insecticidal. The hybrids were backcrossed with the weedy parent, and only half the oilseed rape lines were able to produce transgenic backcrosses. After two backcrosses, the ploidy level and morphology of the resultant plants were indistinguishable from B. rapa. Hybridization was monitored under field conditions (Tifton, GA, USA) with four independent lines of Bt oilseed rape with a crop to wild relative ratio of 1200:1. When B. rapa was used as the female parent, hybridization frequency varied among oilseed rape lines and ranged from 16.9% to 0.7%.

Key words: transgene / oilseed rape / Brassica rapa / hybridization / Bacillus thuringiensis

Correspondence and reprints: C. Neal Stewart, Jr. Tel.: (1) 865 974 7324; fax: (1) 865 974 1947;
    e-mail: nealstewart@utk.edu

© ISBR, EDP Sciences 2002

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