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SUGAR beets genetically modified to resist one herbicide have accidentally
acquired the genes to resist another. The accident provides yet more evidence
that the widespread use of herbicide-resistant crops could lead to the creation
of superweeds.

European regulations forbid the creation of plants resistant to several
herbicides because they might become uncontrollable. However, in September, when
trial plots of beets designed to resist the herbicide glufosinate were sprayed
with glyphosate to kill them off, not all the plants died. In nine plots in
Britain, France and the Netherlands, 0.5 per cent of the crop survived. “That
adds up to a lot of plants,” says Brian Johnson of the government conservation
agency English Nature.

The errant resistance gene crept into the beets in the greenhouses of a
German seed company, says Wolfgang Faust of Aventis in Frankfurt, the company
that created the beets. A few of the beets were pollinated by another variety
engineered to resist glyphosate, making their offspring doubly resistant. “If
they can’t prevent it there, there is little chance they will avoid it in the
field,” says Johnson.

Faust says that such “stacking” of resistance genes is unlikely in beets,
because they flower in their second year and most are harvested in the first.
“But some plants always bolt and bloom in their first year,” responds Johnson.
Their weedy offspring have to be killed with broad-spectrum herbicides. If these
beets acquire additional resistance genes, they can be killed only by more
noxious herbicides.

While only one similar incident of gene stacking has been reported, in
rapeseed in Canada
(NewScientist, 19 February, p 21),
Johnson says there are “informal” reports from the US.