GENET archive


2-Plants: Transgenic crop trial's gene flow turns weeds into wimps

genet-news mailing list

-------------------------------- GENET-news --------------------------------

TITLE:  Transgenic crop trial's gene flow turns weeds into wimps
SOURCE: Nature 421 ( 462), doi:10.1038/421462a, by David Adam
DATE:   Jan 30, 2003

------------------ archive: ------------------

Transgenic crop trial's gene flow turns weeds into wimps

Could 'superweeds' carrying genes from genetically modified crops behave
less like Superman and more like Clark Kent, his puny alter ego? The
first results from a pioneering field trial in the United States suggest
as much - and that the effects of gene flow from transgenic crops may be
less aggressive than some environmentalists predict.

The experiment, run by Neal Stewart and his colleagues at the University
of Tennessee, Knoxville, would have struggled to win regulatory approval
in Europe. In it the team used an oilseed rape crop that had been given a
gene from the bacterium Bacillus thuringiensis (Bt), enabling it to
produce a toxin that repels insects. They crossed the genetically
modified variety with a wild relative, Brassica rapa, then backcrossed
the resulting hybrid with the wild plant again, and released the
resulting 'superweed' into the environment.

The resistant weed's ability to compete as a pest - and therefore the
likelihood of the rogue gene sweeping through wild plant populations -
was assessed by its effect on fields of wheat. In other fields, the
researchers introduced naturally occurring weeds.

The team found that the transgenic weed was far from dominant, having 20%
less effect on wheat yield than the unmodified B. rapa weeds. Stewart
presented his team's results, from the first year of trials in North
Carolina and Georgia, at a conference on gene flow between plants held in
Amsterdam on 21-24 January.

Stewart, who believes that genetically modified crops are currently
"over-regulated", suggests that the modified weeds lose potency because
they are disrupted by the genetic load of crop genes being carried over
with the Bt transgene. "Weeds have undergone years of selection that make
them very good at what they do," he says.

Other plant researchers welcomed the results as an important advance. "We
need to move on from asking whether gene flow takes place, to
investigating what happens when and where it does," says Brian Johnson,
biotechnology adviser to the conservation group English Nature and an
expert on transgenic-crop issues.

But some cautioned that the preliminary results are not a green light for
the use of such crops in Europe, where their commercial planting is under
a de facto moratorium. In a separate study announced last year, plant
ecologist Allison Snow at Ohio State University in Columbus found that
similar Bt transgenes can make wild sunflowers produce more seeds - a
sign that modified wild populations could prosper and spread in the
environment (see Nature 419, 655, 2002).