Concerns have been raised in Europe about the efficiency, sustainability,
and environmental impact of the first genetically modified crops. The
committees and regulators in charge of approving procedures have encouraged
a field trial approach for safety assessment studies under current agronomic
conditions. We describe the gene flow from sugar beet (Beta vulgaris L.) in a multi-year
and multi-crop monitoring study on farmers' fields at two locations that has
been carried out since 1995. We analyzed two sugar beet lines that have been
genetically transformed for herbicide resistance. One sugar beet has
resistance to glufosinate and the other to glyphosate. Large differences
among lines, years and locations were observed. These differences provided a
broad range of situations to estimate the risks. Sugar beet bolters produced
the majority (86%) of the herbicide-resistant seeds harvested in the
field. Direct pollen flow from sugar beet bolters to weed beets that were
growing within the same field as well as in a neighboring field that was
left fallow accounted for only 0.4% of the resistant seeds released over
the years and locations. Descendants of the hybrids between the sugar beet
and the weed beet produced the remaining 13.6% of resistant seeds.
Herbicide-resistant seeds from the progeny of the weed beet were recorded up
to 112 m away from the closest transgenic pollen donor. Indications were
observed of non-randomness of the weed beet producing resistant progeny. We
also analyzed pollen flow to male-sterile bait plants located within and
outside of the sugar beet field. Herbicide-resistant pollen flow was
recorded up to 277 m, and fitted with an inverse power regression. Using
sugar beet varieties with no, or very low, sensitivity to bolting and
destroying bolters are two necessary measures that could delay gene flow.