The risk of crop transgene spread

An environmental concern regarding the cultivation of genetically modified crop plants is whether transgenes can be transferred to wild or weedy relatives by hybridization and backcrossing, potentially resulting in plants with enhanced invasiveness or weediness. The problem has been addressed for several crop-weed systems, but attention has focused on the initial crop-weed hybridization, and there is a lack of experimental data concerning the subsequent stages in the gene transfer process. We have studied the introgression of genes from oilseed rape (Brassica napus) to the weedy relative Brassica campestris (B. rapa). The two species hybridize spontaneously, and hybrids have been found in natural populations. Here we report that transgenic, herbicide-tolerant weed-like plants with B. campestris morphology, the same number of chromosomes as B. campestris, and high fertility, are produced as early as the first-backcross generation in field experiments where transgenic, herbicide-tolerant, interspecific hybrids are grown together with B. campestris.