Farmers Cope With Roundup-Resistant Weeds

This is a big concern, because the trend promises higher food prices and increased environmental destruction. The use of crops which are genetically modified to resist Roundup herbicide, a short-acting herbicide which used to kill just about all plants helped minimize farming practices which were more labor intensive and promoted chemical runoff and soil erosion. But we may have to return to the practices of past decades.

Just as the heavy use of antibiotics contributed to the rise of drug-resistant supergerms, American farmers’ near-ubiquitous use of the weedkiller Roundup has led to the rapid growth of tenacious new superweeds.

But farmers sprayed so much Roundup that weeds quickly evolved to survive it. “What we’re talking about here is Darwinian evolution in fast-forward,” Mike Owen, a weed scientist at Iowa State University, said.

Now, Roundup-resistant weeds like horseweed and giant ragweed are forcing farmers to go back to more expensive techniques that they had long ago abandoned.

The problem is relatively small right now, perhaps 4-5% of the crop acreage is affected by these mutant weeds. But its a growing threat and not just in the US. Major crop producing countries such as Australia, China and Brazil are also affected.

lol, my question in my head was, "How does it get phenylalanine?"

Round-Up is glyphosate, which competitively inhibits an enzyme important in the synthesis of the amino acid phenylalanine. I'm guess that an amino acid change in the active site resulted in an enzyme that doesn't like glyphosate but is okay with the normal substrate.

Mon Santo inserted a bacterial enzyme into their soy plants for phenylalanine synthesis, so they're resistant to glyphosate.

WetCatechumen, I don't think the exact mechanism for Roundup (glyphosate) resistance has been pinned down. However, a study published in the January 19, 2010 issue of the Proceedings of the National Academy of Sciences proposed a possible explanation.

The herbicide glyphosate became widely used in the United States and other parts of the world after the commercialization of glyphosate-resistant crops. These have constitutive overexpression of a glyphosate-insensitive form of the herbicide target site gene, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS).

Aware of the problem of Roundup resistant weeds, the investigators compared populations of one weed species. One population was resistant, the other population was susceptible to the herbicide.

EPSPS enzyme activity from resistant and susceptible plants was equally inhibited by glyphosate, which led us to use quantitative PCR to measure relative copy numbers of the EPSPS gene. Genomes of resistant plants contained from 5-fold to more than 160-fold more copies of the EPSPS gene than did genomes of susceptible plants.

EPSPS gene amplification was heritable, correlated with resistance in pseudo-F2 populations, and is proposed to be the molecular basis of glyphosate resistance.

I don't understand the science involved :o, but it sounds as if the weeds which are resistant have achieved it by simply overproducing the gene which is affected by Roundup. And I think that is roughly the same strategy used in Monsanto's genetically modified crops. However, the company achieved it artificially and the weeds have achieved it naturally.

Competitive inhibition reduces the enzymes affinity for substrate.
Competitive inhibitor binds reversibly to the enzyme’s active site.The inhibitory effect can be overcome simply by increasing the substrate concentration.

I’m assuming the weeds just increase their uptake of phenylalanine.

erm…sort of. I should have written "…by simply overproducing the gene which is not affected by Roundup.

Well, now this will be interesting.

"To fight them, Mr. Anderson and farmers throughout the East, Midwest and South are being forced to spray fields with more toxic herbicides, pull weeds by hand and return to more labor-intensive methods like regular plowing.

“We’re back to where we were 20 years ago,” said Mr. Anderson,"

I am not sure sure Monsanto can make a lot of margin on hand pulling weeds?:rolleyes: How will they be able to patent, people pulling weeds by hand?:cool:

For the next couple of years the farmers will have to use the HIV Cocktail strategy of mixing different combinations of enzyme blocking agents. Who knows they may have to go back to the Thio-Phenol based products like Trithion and the rest, switching from Organo-Phosphates and Organo-Sulfates.:shrug:

Monsanto helped create agent orange. Now they are big manipulator of our food supply.

I remember reading somewhere some years ago that within the next 25 to 40 years, we may be seeing the return of innoculation-resistant TB, polio, smallpox, and all sorts of little goodies that we smugly thought, in our scientific brilliance, that we had “wiped out forever”.

Yeah, we never figured that organisms which have been here for 160,000 years might just figure out a way to adapt.

“It’s not nice to fool Mother Nature!”

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