How about GE cover crops?

posted in: Science | 10
The cover crop, red clover, grows in winter wheat. Photo by Steve Deming; MSU W.K. Kellogg Biological Station via Flickr.
A red clover cover crop grows in winter wheat. Photo by Steve Deming; MSU W.K. Kellogg Biological Station via Flickr.

In a past post, I argued that killing a cover crop with an herbicide was better for building soil than killing it with tillage. Here is another option. Why not develop genetically engineered cover crops that die easily when sprayed with an innocuous substance?

Such cover crops would be a benefit to farmers and the soil. Farmers could use these cover crops to build their soils without worrying that they would undo their progress by having to use tillage to kill the crop. An easy-kill cover crop would make a near-organic no-till system much more practical. Depending on how it was done, herbicide use could be reduced or eliminated.  It might even be possible to place such a GE trait into multiple cover crop species, to be used by farmers in varying cover cropping situations and climates.

A GE cover crop would avoid many of the objections to GE food crops.  Since the engineered organism would not be harvested, the risk of it mixing with non-GE crops is greatly reduced. As a cover crop, it would never get to the consumer – no Frankenfoods here.

Unlike current GE crops, the trait given to these cover crops would not be beneficial to the plant, evolutionarily speaking. The trait would be more like an undesirable mutation, but one that we designed to be of advantage to us. There would be no risk of developing herbicide resistant weeds. Even if the trait did escape to other species, it would be of no advantage and so would not spread rapidly.

As to how this could be engineered, I can only speculate. The ideal would be to modify the plants to be susceptible to a low dose of a cheap substance like vinegar, which organic farmers already use for weed control. Another option would be to make the plants highly susceptible to very low doses of a current herbicide, preferably one that is relatively non-toxic, non-mobile, and readily degraded in the soil. Glyphosate would be a good candidate if not for all the weeds that have become resistant to it.

I found few references to efforts in this area, although with strategies different from mine. In one, researchers engineered plants to die at high temperatures. Although they were successful, they thought that using photoperiod as the trigger mechanism would make the timing of the crop death more reliable than temperature. Another strategy, this one described in a patent held by the Idaho Research Foundation, uses hybrid lethality (also called hybrid necrosis), here in wheat, to make the crop die early, before completing its life cycle.

There would still be challenges, like what to do with the weeds growing in the cover crop, which would not die when sprayed, or when the cover crop died.  The cost of the seed could also be a problem. Farmers typically want low-cost seed for cover crops, but whoever developed this trait would want to recoup costs by increasing the seed price. Perhaps this is where public research could step in and provide a service.

I can imagine other uses for such crops. Farmers could plant them as designer weeds to cover the soil, mimicking the role of weeds and competing with them, but then spray them out before they compete with the cash crop. The trait could be used in species that have allelopathic properties to improve their competitiveness while they are growing and after they are killed. Other possibilities are genetically engineered mustard cover crops designed to produce high levels of the desired glucosinolates in the roots or high dhurrin-producing sudangrass for control of nematodes.

There will still be those who object to GE plants in any form. However, for those whose concerns are specifically with using GE crops for food, this may be acceptable. The linking of genetic engineering with soil building cover crops could be a different model for future genetic development.

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Andrew McGuire is an Irrigated Cropping Systems Agronomist for Washington State University Extension. He works with farmers in the Columbia Basin of Central Washington in improving soils through cover crops and high residue farming systems.

  • Weeds growing in the cover crop would definitely be a challenge, but this technology would be very useful if paired with strong weed-blocking cover crops such as sorghum sudangrass.

    I grow sorghum sudangrass cover crops b/c IMO it’s one of the best covers for coaxing starved soil back to health AND it blocks weeds, but killing it is a problem for me. I’m committed to no-till and prefer not to use herbicide because my farm had a horrendous superweed outbreak in the recent past. So I rely on a hard frost to kill, which is too late to get the next cover crop cocktail established and growing before winter sets in.

    So a GE cover crop like you describe could solve my timing problem.

  • Dylan

    Wouldn’t you have the same issue of “herbicide” resistance when it is time to kill off the cover crop?

    • Good question. Dylan, I am not a weed scientist, but I don’t think so. Because this is not a weed, it would not be present in the field all the time like weeds are, thereby receiving every herbicide application. Assuming that it is managed well and has no hard seed (germinates years after you plant it), this would greatly reduce the selection pressure for resistance.

      Also, unlike weeds, these would be engineered to die when exposed to a specific chemical, which, I think, would also reduce the chance of resistance developing.

    • Ewan R

      I think Anastasia’s proposal was to use a non-herbicidal molecule to trigger the death of the plant (so… basically she’s proposing a suicide gene…) thus the only population you’d have to worry about being resistant would be the covercrop itself – and given that it should come from a certified seed producer each year it’s not likely to be up and evolving resistance – resistant seed would either be non-transgenic or simply broken, and would be the fault of the seed producer.

      • Did Anastasia propose this already? I easily could have missed it as I am relatively new to this blog and have not caught up on my reading.

        • Ewan R

          No apparently I don’t read beyond the first letter of someone’s name though… totally misattributed…

          • lol I was going to say – I know I have pregnancy brain but I totally don’t remember that!

  • Keith Hayes

    I see your points Andrew, but I think purists in the organic food movement would be opposed to the use of any GMO in organic agriculture even if it wasn’t to be consumed by humans. Many of them see adoption of GMO’s in any fashion as caving in to big ag.

    • Brenna

      I would find it interesting to see what spin “purists” could put on this idea, particularly if it was a suicide gene rather than requiring heavy doses of herbicide to kill. I tend to lean organic, but also feel I can be reasonable when it comes to biotech. The only time I see most people upset is when we are talking about food… although I might venture a guess that many don’t realize how many GMOs are actually out there already.

  • Stan Ford

    We already have crops that frost kill, but it is interesting. The frost killing of course only works on fall cover crops. Heat killed plants a little harder, but then again they is why they developed crimper/rollers. A lot is going to depend on where you are.