James and the Giant Corn Genetics: Studying the Source Code of Nature

October 8, 2009


Filed under: agriculture,biology — James @ 5:46 pm

I’m sure everyone reading this has heard the term ‘superweed.’ These are the terrible new creations that will, or in some cases have, been created by herbicide resistant crops. What makes them so super and terrible? They’re resistant to the same herbicide as the herbicide resistant crop they grow among. Treating crops with herbicides selects for herbicide resistance crops in the same way treating infections with antibiotics selects for antibiotic resistant bacteria. Taking antibiotic drugs kills all the bacteria susceptible to the antibiotic. That means any individual bacterium which can survive the treatment is much more likely to reproduce and thrive now that all its competitors were killed by the drug. In the same way, spraying fields with an herbicide, while good at killing off weeds, also gives a big selective advantage to any weeds that carry traits which allow them to survive the spray. Thusly are the superweeds born. Why isn’t that the end of the world? Read on the find out.

The whole point of engineering a crop to resist a specific herbicide is to create a difference between the crops and the weeds so a farmer can kill weeds but not his or her crops. Once the weeds are resistant to the herbicide, just like the crops are, the difference is gone. So there’s no point in spraying the herbicide, and no point in buying the seed engineered to resist it. Things are right back where they started, only the farmer has had years or decades of effective weed control in between.

That is ALL superweeds do, nullify the advantage of the herbicide resistant crops that drove their creation. Just like an antibiotic resistant infection is no worse than an untreated resistant infection, an herbicide resistant weed is no more damaging than a normal weed, it simply grows under a single condition that would kill that normal weed (the application of a particular herbicide).

That’s why superweed is a misleading name. As superpowers go, superweeds are less like a spiderman or a superman and more like ta man who was bitten by a radioactive octopus and now can still be killed by all the usual things EXCEPT drowning (and still passes out from lack of oxygen so he can’t even do cool things underwater). Superweeds aren’t something to be happy about, but they’re not the end of the world as we know it. And since the danger of a superweed is only that it’ll reverse the benefits of using the the herbicide resistance/herbicide system that created it, its silly to argue we shouldn’t use the technology because using it might eventually reduce the benefit of using it.

That’s not to say we shouldn’t try to slow or prevent the development of resistance while using the technology. Fortunately, biologists know a lot about slowing evolutionary selection. For BT crops, that are toxic for insects (while being safe for humans, all about acidic vs basic digestive systems), farmers can and do plant refuges of non-BT plants so any insects that survive the BT toxin will have their resistant genetics diluted by mating with the non-resistant insects living in the refuge. People who are infected with HIV are treated with a mixture of three or more anti-HIV drugs to prevent selection for resistant strains of the virus. Occasionally, by chance, a virus will mutate to get resistance to one of the drugs, but since its still killed off by the other two it never receives an evolutionary advantage and so the mutation never spreads to the rest of the population. In the long term I imagine something similar could and should be developed for herbicide resistant crops, with resistance to multiple herbicides, with unrelated modes of action*, so there is little evolutionary selection for resistance to any one of the chemicals individually.

But regardless of what happens in the future, doesn’t it seem silly for people who are mostly opposed to herbicides (an GMOs) in the first place to blame the latter for the chance that it might render the former less effective?

*The mode of action is what the chemical in the herbicide does to the plant to kill it.

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