The bans were originally put in place in 1998 because of concerns about gene escape
into the environment.
That means transgenic plants created by the T-DNA vector system have a ready route for horizontal gene escape, via Agrobacterium, helped by the ordinary conjugative mechanisms of many other bacteria that cause diseases.
(15.) McNicole et al (1997) The Possibility of Agrobacterium as a Vehicle for Gene Escape. MAFF.
He is little concerned about the gene escape
into wild plants to produce "superweeds," because a cross between a GM crop and a wild relative will involve all of the GM crop's genome, including the characteristics that make it dependent on the tender loving care of the farmer for survival.
* Kansas State University, Manhattan, Kansas -- $160,000 to study potential gene escape
in imidazolinone resistant sunflowers and the impact on related wild species.
Radish as a model system for the study of engineered gene escape
rates via cropweed mating.
They exacerbate weed problems in two ways:  by the natural evolution of herbicide resistant weeds through repeated exposure to herbicide and;  by gene escape from crops to natural populations of plants.
Gene escape from cultivated plants is documented for crops including cotton, cucumber, corn, millet, canola, quinoa, radish, rice, sorghum, strawberry, sugarbeets, and watermelon.
What are the ecological consequences of gene escape? It depends upon the nature of the engineered trait.
Once an engineered gene escapes
into the natural environment, it spreads rapidly and has the potential to alter plant evolution.
Most previous studies of gene escapes
have focused on pollen straying far and wide, says Jean-Francois Arnaud of the Universite de Lille 1 in France.