Geneticists create 'next generation' of GM crops*

Soya beans and cotton could be treated with alternative herbicide.

Heidi Ledford

Dicamba-resistant crops could give soya farmers more options to beat weeds.

Brett Hampton / University of Nebraska Institute of Agriculture and
Natural Resources

Researchers have created what could be the next generation of transgenic
crops by inserting a gene for herbicide resistance from a bacterium into
plants. The new crops could help to combat the spread of resistance to
other commonly used herbicides.

The approach is not a new one — many farmers already grow crops that
have been engineered to resist the herbicide glyphosate. But the new
plants are resistant to a compound called dicamba, and could offer
farmers an alternative in areas where glyphosate-resistant weeds have
become a problem.

Dicamba, which kills broadleaf weeds but spares grasses, has been used
for decades to protect fields planted with corn, a member of the grass
family. The researchers have now created transgenic soya beans, tomatoes
and other broad-leaved crops that are resistant to this herbicide — a
development that will expand the range of dicamba's uses.

Dicamba lasts only a few months in soil, and rarely contaminates water
contamination is rare. The chemical itself is stable, but it is quickly
devoured by hungry hordes of microbes living in the soil.

Shuffling genes

Don Weeks and his collaborators at the University of Nebraska in Lincoln
isolated a gene from Pseudomonas maltophilia that is responsible for the
breakdown of dicamba. They then transferred this gene into tobacco, soya
beans, tomatoes and the model plant Arabidopsis thaliana. In every case,
the plants became resistant to dicamba, the researchers report in this
week's Science.1

Monsanto, the makers of the 'Roundup Ready' line of glyphosate-resistant
crops in St Louis, Missouri, has already licensed the dicamba
technology. The company says it hopes to make dicamba-resistant soyaa
beans available commercially in three to seven years, with cotton to
follow after that. Monsanto does not market dicamba itself.

Farmers will probably embrace the crops, says Robert Hartzler, a weed
specialist at Iowa State University in Ames. "It's definitely going to
help some of the problems that are developing with our heavy reliance on
glyphosate," he says.

Some 90% of soya-bean crops in the United States and 60% of its cotton
are genetically engineered to resist glyphosate. Although critics argue
that transgenic technology encourages use of herbicides, advocates say
that the crops have helped many farms to stop tilling the earth before
they plant — a practice that causes added soil erosion and water
pollution. Instead, farmers can plant glyphosate-resistant crops
directly after 'burning down' existing weeds with glyphosate.

The problem is that glyphosate-resistant weeds are on the rise,
particularly on farms that do not till. And this issue threatens to
drive up the cost of no-till farming, sending farmers back to their old
tilling ways, says William Johnson, a weed specialist at Purdue
University in West Lafayette, Indiana.

But dicamba comes with problems of its own, says Hartzler. The
compound's volatility means that it can kill off broad-leaved plants on
fields and houses up to half a kilometre away, meaning that farms close
to sensitive areas such as vineyards or private gardens may not be able
to use dicamba-resistant crops. "It's one of the most common consumer
complaints that I deal with," notes Johnson.

Hartzler says that this 'dicamba drift' is more a cosmetic nuisance than
an ecological disaster. Weeks, who along with his collaborators stands
to receive royalties from Monsanto for products developed from their
discovery, adds that farmers have decades of experience with dicamba,
and management techniques are already well established.

What's more, over the 40 years of dicamba use, only a few isolated
dicamba-resistant weeds have sprung up, and they have not posed a threat
to agriculture. But that's not to say that resistance won't become a
problem with more widespread future use. "I don't think we can say
resistance won't develop," says Hartzler, "but it is a much lower
likelihood than with other herbicide classes. But then, that's what they
originally said about glyphosate."