Stable Bacillus thuringiensis (Bt) toxin content in interspecific F-1 and backcross populations of wild Brassica rapa after Bt gene transfer

Stable expression of a transgene may lead to increased fitness for wild plants after acquiring the transgene via crop-weed hybridization. Here, we investigate the stability of Bt toxin content in wild Brassica rapa acquiring the Bt gene from Bt Brassica napus. The Bt toxin content in nine Bt-expressing B. napus lines was 0.80-1.70 mug/g leaf tissue throughout the growing season. These nine lines were crossed with three accessions of wild B. rapa and the Bt gene was successfully transferred to interspecific hybrids (F-1) and successive backcross generations (BC1 to BC4). The Bt toxin level in F-1 and BC progenies containing the Bt gene remained at 0.90-3.10 mug/g leaf tissue. This study indicates that the Bt gene can persist and be stably expressed in wild B. rapa.