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Nitrogen-fixing maize – with or without biotech?

One way to improve profitability, is to reduce input costs. When it comes to maize, one of those inputs – and a particularly significant one at that – is nitrogen fertiliser. But how much could you save if your maize, like legumes, could fix its own nitrogen?

Thanks to modern understandings of genetics, researchers from the University of Wisconsin in the United States now hypothesise traits from modern maize’s most ancient ancestor could be reintroduced to produce nitrogen-fixing maize.

This, they say, is not a future aspiration; despite not knowing which specific gene triggers nitrogen fixation, that benefit could be accomplished today through traditional plant breeding. Fan that I am of modern (and unfortunately controversial) genetic technologies, that seems like a boon.

Benefits from the Mountains of Mexico

According to Dr. Vania Pankievicz, a researcher from the University of Wisconsin’s bacteriology and agronomy departments, farmers in Mexico’s southern Oaxaca state grow a variety of Maize that doesn’t require nitrogen fertiliser.

The variety in question is a very long-season indigenous maize landrace (locally created cultivar) called Sierra Mixe. Growing between 15 and 20 feet (5 to 6 metres) in height, this landrace is produced year after year in nitrogen-deprived soils, and without nitrogen fertiliser.

Nitrogen-fixing bacteria

In presenting to Ontario farmers at an environmental farming conference earlier this year, Pankievicz said she and other university colleagues – including Dr. Jean-Michel Ané, the project’s lead researcher – now know the key to Sierra Mixe’s natural nitrogen success is its ability to produce an abundance of “aerial roots” – plus mucilage, a glycerin-like substances excreted from those areas of the stalk, and one rich in nitrogen-fixing bacteria.

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Aerial roots are above-ground roots that grow from nodes on the maizestalk. - Photo Courtesy of Dr. Jean-Michel Ané, University of Wisconsin
Aerial roots are above-ground roots that grow from nodes on the maizestalk. - Photo Courtesy of Dr. Jean-Michel Ané, University of Wisconsin

Large roots from about 10 nodes per plant

Aerial roots are above-ground roots that grow from nodes on the maizestalk. While standard commercialised maize varieties produce small roots from about 3 nodes per plant, Sierra Mixe maize produces large roots from about 10 nodes per plant. Mucilage production is similarly much higher. Constantly rehydrated by the Oaxaca region’s tropical rains, that mucilage drips onto the soil where the bacteria within can make nitrogen available to the plant.

Pankievicz says the current hypothesis for the genetic origins of Sierra Mixe’s bacteria-filled mucilage production – and consequently, the ability to absorb nitrogen naturally – comes from Mexicana, an ancient maize ancestor common to both it as well as commercial maize. In modern varieties, she says, this trait was lost as new varieties were developed and grown in environments with high nitrogen pressure; that is, with lots of seasonally applied fertiliser.

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Dr. Vania Pankievicz Pankievicz says there is no reason the genetic characteristic can’t be reintroduced right now via traditional breeding with Sierra Mixe. - Photo: Matt McIntosh
Dr. Vania Pankievicz Pankievicz says there is no reason the genetic characteristic can’t be reintroduced right now via traditional breeding with Sierra Mixe. - Photo: Matt McIntosh

Reintroducing genes

What gene specifically allows Sierra Mixe and Mexicana to naturally absorb nitrogen has not yet been discovered, though it is being explored. Once that has been determined, modern genetic manipulation techniques could be employed to quickly incorporate the ability into high-productivity commercial varieties. The same could then be done for other grass and cereal crops as well.

Also read: Pioneer CRISPR-Cas: GMO rules frustrate innovation

However, Pankievicz, says there is no reason the genetic characteristic can’t be reintroduced right now via traditional breeding with Sierra Mixe. This, she says, would be highly effective from a regulatory perspective (less biotech-related baggage) and prove to be the quickest way to commercialisation.

Breeding program

Pankievicz believes the next step is to continue investigating how the trait works while starting a breeding program. Doing so, she says, would complement long-standing research initiatives looking for nitrogen-fixing bacteria strains that will associate with maize – as happens with legumes. Together, success in both research areas would help develop even less nitrogen-dependent yet commercially-viable maize varieties.

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Realistic impact?

If high-productivity nitrogen-fixing maize is realised, farmers worldwide could benefit – that would ideally include the largest producers in the American Midwest as well as the poorest growers of Africa. Really making these theoretical nitrogen-fixing varieties work, of course, would likely require some agronomic finesse at the field level, to be sure.

The cynic within my own mind, though, makes me question how successful nitrogen-fixing commercial maize would be

But the prospective financial fertiliser savings certainly make this worth exploring. Given this author’s proximity to North America’s Great Lakes region and the ongoing nutrient runoff issues experienced there, musing poetically about a natural reduction in water-borne nitrates is another tantalizingly positive possibility.

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Mucilage drips onto the soil where the bacteria within can make nitrogen available to the plant. - Photo Courtesy of Dr. Jean-Michel Ané, University of Wisconsin
Mucilage drips onto the soil where the bacteria within can make nitrogen available to the plant. - Photo Courtesy of Dr. Jean-Michel Ané, University of Wisconsin

The cynic within my own mind, though, makes me question how successful nitrogen-fixing commercial maize would be. This is particularly true if such varieties were developed through biotechnology. The differences between regulatory environments and (often visceral) political rhetoric around biotechnology in places like Canada, the United States, and the European Union are themselves several elephants in a small room.

Regulatory challenges

As much as it pains me to say it, perhaps achieving this biological breakthrough over the course of years via traditional breeding is the best approach to take. Doing so, one would hope, might remove many of the regulatory challenges associated with commercializing biotech-crops, and leave far less room for particularly-zealous special interest groups to stymie development and dissemination.

As an aside, this piece may have become a vector for a wider political discussion about science and policy. So, apologies to you, dear reader.

Regardless, nitrogen-fixing maize is an interesting prospect, however it might be realised.

2 comments

  • M Stephens

    How will this function in the dry climate in most of the major maize growing regions

  • M Stephens

    I would not reject any effort to deliver nitrogen fixation to maize but breeding even today takes a long time especially when you need to move genetics into thousands of corn inbreeds. We already have biological nitrogen fixation delivered by microbes via the pivotbio product just introduced

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