What ancient corn farmers can teach us about engineering crops for climate change

What ancient corn farmers can teach us about engineering crops for climate change

In the era of GMO crops, farmers can learn old lessons of diversity

Gabriela Serrato Marks

Marine Geology

Massachusetts Institute of Technology

There are more than 50 strains of maize, called landraces, grown in Mexico. A landrace is similar to a dog breed: Corgis and Huskies are both dogs, but they were bred to have different traits. Maize domestication worked the same way.

Some landraces of maize can grow in really dry conditions; others grow best in wetter soils. Early maize farmers selectively bred maize landraces that were well-adapted to the conditions on their land, a practice that still continues today in rural areas of Mexico.

If you think this sounds like an early version of genetic engineering, you'd be correct. But nowadays, modern agriculture is moving away from locally adapted strains and traditional farming techniques and toward active gene manipulation. The goal of both traditional landrace development and modern genetic modification has been to create productive, valuable crops, so these two techniques are not necessarily at odds.

Corn cob DNA

Jason Wallace / Wikimedia

But as more farmers converge on similar strains of (potentially genetically modified) seeds instead of developing locally adapted landraces, there are two potential risks: one is losing the cultural legacy of traditional agricultural techniques that have been passed on in families for centuries or even millennia, and another is decreasing crop resilience even as climate variability is increasing.

From weed to tortilla

Mexico is the main importer of US-grown corn, but that imported corn is primarily used to feed livestock. The corn that people eat or use to make tortillas is grown almost entirely in Mexico, which is where landraces come in.

It is a common practice to grow multiple landraces with different traits as an insurance policy against poor growth conditions. The wide range of landraces contains a huge amount of genetic diversity, making it less likely that one adverse event, such as a drought or pest infestation, will wipe out an entire crop. If farmers only grow one type of corn, the whole crop is vulnerable to the same event.

Landraces are also different from most commercially available hybrid strains of corn because they are open pollinating, which means that farmers can save seeds and replant them the next year, saving money and preserving the strain. If a landrace is not grown anymore, its contribution to maize's genetic diversity is permanently lost.

Domesticating maize

John Doebley, University of Wisconsin Madison

This diversity was cultivated over generations from maize's wild cousin, teosinte, by 60 groups of indigenous people in Mexico. Teosinte looks like a skinny, hairier version of maize. It still grows wild in some parts of Central America, but its close relatives have been found, domesticated, at archaeological sites in the region over 9,000 years old. These early maize cobs could easily fit in the palm of your hand – not big enough to be a staple crop that early farmers could depend upon for sustenance. Genetically, they were more similar to wild teosinte than to modern maize.

Until recently, historians and scientists alike weren’t sure how long it took for maize to spread outside southern Mexico, and what that spread did to its genetic diversity. Moreover, they were unsure how maize transformed from a skinny weed into a productive crop eaten across the world.

That uncertainty changed when Douglas Kennett, professor of environmental archaeology at Penn State, and several colleagues from anthropology departments around the US, started working on a rock shelter in Honduras with thousands of fossilized cobs. In a study published this past summer, they found that maize was a staple food crop in the region by 4,300 years ago.

Young Maya Corn God

The Met

To figure out how productive the maize was, they ended up using a low-tech method with a fancy name: morphological analysis – aka, looking at lots of corn. If the cobs were too small, it would mean that maize wasn't a staple crop yet. They found the opposite: the cobs were large enough to suggest that farmers had selected for highly productive types of maize and were using it as a staple food crop. The archaeologists also found that the cobs in Honduras, which is outside the natural range of teosinte, were larger than cobs of the same age from the original domestication region in southern Mexico. The scientists think that people in Honduras were able to develop more productive maize landraces because their crops were isolated from wild teosinte.

The size and shape of the ancient cobs from Honduras show that early farmers engineered the maize crop to make it more productive. They developed unique landraces that were well adapted to local conditions and successfully cultivated enough maize to support their communities. In many ways, they were early geneticists. However, in contrast to modern genetic modification, which strives to make things uniform, they were able to preserve the huge amount of genetic diversity present in maize. In fact, there is more genetic diversity in domesticated maize than in wild teosinte.

Crucial diversity

We have a lot to learn from the indigenous farmers who were growing maize 4,000 years ago. Their history provides examples of both environmentally sound genetic modification and effective adaptation to climate variability. As droughts and storms alike become more severe and frequent, crops will need to live through more extreme weather than they do now.

Flickr/Jay Galvin

Early farmers from Mexico to Honduras (and beyond) dealt with similar environmental differences by developing their own locally adapted landraces. In regions that are cold or dry, local landraces grow better than commercially available strains. Moreover, the genetic diversity preserved in landraces means that modern farmers still have a wide library of traits to choose from. Wiping out this valuable diversity by switching to hybrid crops that are not open pollinating will make maize crops far more vulnerable to adverse events.

In addition to the genetic motivation to preserve maize landraces, there might be a culinary push to keep the varieties around. Unfortunately, the mass-produced tortillas most people in the US and Mexico eat are a far cry from homemade, small-batch tortillas that only contain corn, slaked lime (to break down the kernels and make them more nutritious), and water. People argue that specialized landraces actually have better flavor than typical corn varieties (I happen to agree with them).

Creating a market for traditional landraces of maize creates an increased commercial incentive to grow them and may be the way forward for preserving the resilience of this important and delicious crop. And that would be better for all in the long run, when an increasingly unpredictable climate will require plenty of options for our food sources to continue thriving. Staying true to the traditions of the past may actually be the key to surviving into the future.

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Devang Mehta

Synthetic Biology

ETH Zurich

While I broadly agree with the author’s core point that we can learn much from studying ancient plant varieties, there are several points in this article I disagree with:

  1. Starting with the claim that “modern agriculture is moving away from locally adapted strains and traditional farming techniques and toward active gene manipulation,” that's simply incorrect. The vast majority of new plant varieties on the market are produced using the same principles of genetic selection practiced by ancient Mexican farmers (and farmers in other civilizations) rather than genetic engineering.
  2. You write that, “If a landrace is not grown anymore, its contribution to maize’s genetic diversity is permanently lost.” This is not true. Many countries as well as international organizations work hard to preserve seed varieties that are no longer in favor. These seed banks are a great resource and offer an opportunity for further genetic improvement using conventional plant breeding, genetic engineering and genome editing.
  3. Much is made about how hybrids cannot be replanted, as you mention, but this is an acceptable trade-off to most farmers since the benefits and productivity offered by modern hybrids are unparalleled. I resent the implication in the piece that farmers are passive actors with no self-interest or capacity to innovate. In fact most of the tremendous yield increases of the last century (including the Green Revolution that saved millions of lives) were driven by publicly funded breeders and innovative farmers. All of this is not to dismiss the importance of landraces and wild relatives to modern agriculture; landraces and wild species are great resources (and are often used as such) for bringing sources of pathogen resistance or traits like drought resistance into modern high yielding plants. It is however, impractical to ask farmers to abandon profitable modern varieties for ancient landraces which cannot compete in yield.
  4. You write that “modern genetic modification... strives to make things uniform.” This is absolutely not the case. Genetic engineering seeks to deliver targeted trait improvements in a quicker, more precise manner than breeding. It has been applied to engineer virus resistance in papaya, cost-saving herbicide resistance in many crops, insect resistance to reduce insecticide use and increase micronutrient content in rice, wheat and even orphan crops like cassava. These are hardly “uniform” changes.
  5. On the question of flavor: yes, it is true that breeding priorities throughout history have prioritized yield over subjective traits. This is changing, although in a world where we still cannot feed everyone, yield remains (and should remain) the most important parameter for a successful agricultural system.
  6. Lastly, breeding, both hybrids or landraces, takes time, which is in short supply due to climate change. Genetic engineering and genome editing are tools that can speed up this process tremendously and should be used to harness the genetic diversity of landraces.

Gabriela Serrato Marks responds:

  1. Large farms are primarily using commercially available seeds, some of which are genetically engineered. That is different from how maize is grown by small-scale farms in Mexico, and is certainly different from how maize was originally domesticated/cultivated. 
  2. Storing some varieties in seed banks is not the same as having landraces actively grown. I’m not very familiar with how seed banks operate, but your article says that “a lot of seed bank material is left uncharacterized and unused.” I don’t think a farmer in Oaxaca will ever have access to a seed stored in the Svalbard bank, for example.
  3. There is cultural significance and a long history attached to maize landraces, and it would be unfair to diminish the importance of that history when arguing about which crops are best.  On the issue of farmers, I am actually making the opposite argument to what you suggest: I am trying to show that innovative farmers, either 4,340 years ago or now, have the tools – landraces – to adapt to climate variability. In Mexico, “profitable modern varieties” have actually not been adopted instead of landraces, which is why there are still more than 50 landraces grown today. Small-scale farmers tend to favor landraces and grow multiple types, because that approach increases yield and provides insurance against one event wiping out the entire crop.  I am not asking anyone to “abandon” improved varieties (they’re not being widely used by smallholders), but I do think it is unfair for western scientists to come into Mexico and Central America and tell (mostly indigenous) farmers to grow commercially available, hybrid seeds, when it is working just fine to use landraces.
  4. I appreciate the clarification. Perhaps it would make more sense to compare growing multiple landraces to monoculture, which could become more prevalent if commercial hybrids are marketed as the best solution.
  5. I am not an economist, but the argument about flavor shows that there is cultural and culinary demand for landraces. If we (as consumers) continue to increase the demand for landraces, that will support the market for these maize types.
  6. I completely agree with you that we should use genetic techniques to create improved crops, but I think it is important to continue to grow current landraces to preserve their traits and allow for targeted genome edits if that technology becomes more widely available. we should learn from early maize cultivators, who prioritized genetic diversity and were early genetic engineers.

Devang Mehta responds:

A couple follow-ups:

  • A lot of corn grown in Mexico are hybrids (30 percent) and this is increasing. Mexico in fact has the premier institute for maize and wheat breeding, CIMMYT (which spearheaded the Green Revolution). Mexican farmers grow a small amount of landraces for home consumption but this method of production can never feed 9 billion people. So a lot of this technology is actually home-grown rather than imposed by ‘western scientists.’
  • There is an ongoing effort to harness the material in seed banks for farmers like the ones you speak of. I get what you say about cultural history, but that culture can be kept alive and shared if these landraces are brought into breeding programs worldwide rather than remaining a niche product grown in only Mexico. In other words, I want some of those amazing tortillas too!

Gabriela Serrato Marks responds:

It sounds like we broadly agree that landraces are a valuable genetic resource!

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