By Sarah Crespi, Angela Saini, Erik Stokstad
October 30, 2023

HIGH HOPES FOR SHORT CORN
Plants bred or engineered to be short can stand up better to windstorms. They could also boost yields and benefit the environment

On 10 August 2020, a record-breaking windstorm raced across Iowa, the big buckle of the U.S. Corn Belt. Gusts up to 225 kilometers per hour flattened fields and buildings, with losses totaling an estimated $12 billion across several states. “It was devastating,” says Kelly Gillespie, a crop physiologist with Bayer Crop Science, who recalls driving by ruined houses and wrecked silos. About 16% of Iowa’s corn and soybean crops were damaged or destroyed. “Corn snapped and broken for as far you could see.”

In the midst of the destruction, though, Gillespie saw glimmers of hope. When she and other researchers visited fields of experimental corn plants developed by Bayer, they saw that most of the plants had resisted the force of the storm and remained standing. The source of their strength? They were shorter.

To an interstate traveler—or anyone lost in a corn maze—the most impressive feature of corn is its stature. Modern corn can grow twice as tall as a person, but height has drawbacks, making the plants vulnerable to wind and more difficult for farmers to tend. Plant scientists think corn can be improved by making it shorter, and leading seed companies are doing that through both conventional breeding and genetic engineering. Bayer has launched a short variety in Mexico, another company is selling its versions in the United States, and more are getting involved.

Researchers say short corn could be a boon for farmers. “This is an idea long overdue,” says Rex Bernardo, a corn breeder and geneticist at the University of Minnesota. “I’m quite excited.” In addition to bolstering wind resistance, the short stature will allow farmers to drive tractors into their fields longer into the summer to add late-season fertilizer or fungicides to boost the harvest. And according to Stine Seed, a company that has pioneered short corn, the new crop can increase yield even further because it can be planted more densely.

Bayer is now wrapping up its final round of U.S. trials, which took place this summer across 12,000 hectares in Iowa and three nearby states. The company plans to start selling seed to U.S. farmers next year,and at least one other large seed company, Corteva Agriscience, will soon follow suit with its own varieties. Bayer’s corn was conventionally bred with the Midwest Corn Belt in mind, but the company has recently developed a transgenic version it can quickly and efficiently tailor to other regions. In June, it was approved by the U.S. Department of Agriculture (USDA), a key regulatory step.

The new corn varieties join a long tradition of improving crops by shrinking them. In the 1950s and ’60s, plant breeders created semidwarf varieties of rice and wheat, allowing plants to bear more grain without collapsing. These high-yielding varieties were key to the Green Revolution, and they prevented famines in developing world. Now that researchers have pieced together the complex interplay of genes and hormones that control corn growth, the time may be ripe for corn, too, to go big by getting shorter.

CORN (ZEA MAYS) was a much different plant when it was domesticated in southern Mexico some 9000 years ago. Compared with modern corn, its closest living relative, a lanky wild grass called teosinte, looks disheveled, with multiple stalks and tassels that mature into many small cobs with just two rows of seeds. In what would be a nightmare for farmers, teosinte’s seeds fall off, rather than clinging to the cob for easy harvest. Some of the oldest corn cobs uncovered by archaeologists are also tiny and fragile. But after millennia of selective breeding—first by Indigenous farmers, and later in universities and multinational companies—corn has become one of the world’s dominant food crops. In the United States, it brings in about one-third of income from all crops, earning farmers $89 billion in 2022.

With success came stature. Over the past half-century, as breeders selected for larger ears with more numerous and plumper, heavier kernels, they ended up choosing big plants with many leaves for photosynthesis and tall stalks. Modern corn plants can grow up to 4 meters high, although the dominant starchy varieties in the U.S.—88% is used for livestock and ethanol—range between 2.5 and 3.5 meters.

Tall plants have an inherent weakness, however. The weight of the ears, usually more than halfway up the stalk, makes the plant vulnerable to snapping or tipping over in strong winds. Making corn shorter isn’t the only remedy, notes Tony Vyn, an agronomist at Purdue University. Breeders have also selected for stiffer stalks, as well as for resistance to stalk rot, which made earlier corn varieties more prone to snap under the weight of their grain or blow over in windstorms.

Even so, between 2001 and 2016, about 800,000 hectares of corn fields were damaged by high winds, according to U.S. government crop insurance claims. That’s not much compared with the 38 million hectares damaged by drought during the same period, but enough that companies see it as a selling point for short corn.

Severe windstorms wreak havoc on fields of tall corn, like this one in Iowa laid low by a derecho in 2020.LISA SCHMITZ/NATIONAL WEATHER SERVICE/WIKIMEDIA

Bayer has used conventional breeding to create three short hybrid varieties that were tested for the U.S. market this summer and are now being harvested by about 300 farmers. Field trials demonstrated better wind resistance compared with tall corn, Gillespie says. “Seeing the standing corn for the first time just gave me goosebumps.” The 2020 windstorm provided an even more strenuous test. Afterward, Gillespie and colleagues analyzed 14 experimental fields that were hit by heavy winds; on average 25% of short corn was damaged compared with 50% of tall corn, they reported in Crop Science in August 2022.

Corteva, which owns the famous seed company Pioneer Hi-Bred International, is aiming for similar results with its conventionally bred short corn, which it hopes will be ready for market in a few years. Corteva researchers test the strength of new hybrids by exposing them to gusts of up to 160 kilometers per hour from a wind machine.

Breeding shortness into an existing variety of corn typically takes 5 years or more. To shortcut this process, Bayer has turned to genetic engineering. Speed is important because Bayer sells about 200 varieties of hybrid corn tailored to various conditions, such as climate and disease threats. Creating short versions of all those varieties through conventional breeding, and making enough hybrid seed to sell, would be prohibitively time consuming.

Bayer’s genetic engineers have focused on a plant growth hormone called gibberellin. At first the approach looked unpromising. Decades ago researchers knocked out the genes that control early steps in gibberellin synthesis, but the result was plants that had deformed flowers and abnormal ears. Since then, scientists have adapted an approach previously used to engineer shorter versions of tomato, apple, banana, and other crops. They figured out how to suppress corn genes that code for enzymes known as gibberellin 20 oxidases, which put the biochemical finishing touches on the hormone in particular parts of the plant. This way, the levels of gibberellin can be lowered in the stalks, but not the flowers, stunting the plants’ growth without undermining their productivity.

Initial attempts resulted in corn plants that were far too short to be commercially viable. But after considerable tinkering, Gillespie and her colleagues solved the problem in collaboration with the company BASF. They added DNA that encodes microRNAs, small molecules that can suppress genes. In this case the targets were two genes that regulate the creation of gibberellin mainly in the leaves and stalk, resulting in plants that were one-third shorter. To avoid shrinking the leaves as well, the researchers delivered the mutant alleles with a genetic switch from a rice virus that is most active in the stalk.

Field studies in 2019 and 2020 at two locations in Illinois confirmed the manipulation did not affect the ears; they weighed the same as those from typical tall varieties, Gillespie and colleagues reported in March 2022 in the Plant Biotechnology Journal. This successful change in stature by interfering with gibberellin was “the first of its kind in corn,” says Guri Johal, a corn geneticist at Purdue who has discovered a mutation, called D16, with a similar effect.

Short but sturdier

Tweaking growth hormones through breeding or genetic engineering can create shorter corn plants by reducing the length of stalk segments between leaves. The plants are sturdier because the ears grow closer to the ground, lowering the center of gravity. The plants also tolerate tight spacing, thanks to more upright leaves. A smaller tassel allows more light to reach the leaves.

Some of the time saved with transgenic corn is lost because of stricter regulatory requirements. Companies must provide field and laboratory data to USDA, which assesses whether genetically modified crops pose a threat to agriculture, and they consult with the U.S. Food and Drug Administration for checks on food safety. Because Bayer’s version will be paired with a transgenic trait for pest resistance (Corteva’s likely will, too), the Environmental Protection Agency will have to evaluate it as well. The reviews can take years.

To speed up the process, Bayer and other companies are working on short corn made with gene editing, an approach that can alter gibberellin without adding genes from other species. Corn varieties created this way will face fewer regulatory hurdles in the U.S. and some other countries, but they’re still years away.

IN SINALOA, MEXICO, where luxuriant corn fields carpet the plains between the Sierra Madre mountains and the Gulf of California, short corn is already having an impact. The farms are some of the most productive in Mexico but have long suffered from large, persistent windstorms called derechos. In 2007, Bayer began to breed a short corn for the region’s farmers by selecting varieties with a mutation that limits transport of another growth hormone, auxin, in the stalk. The resulting plants are about one-third shorter than normal, and less likely to fall over or snap in a derecho. (This variety, which went on the market in 2020 as VITALA, isn’t suitable for use in the United States because it is tailored to the soil and climate in Sinaloa, as well as the day length at that latitude.)

At a February agricultural trade show in Culiacán, Sinaloa’s capital, Bayer highlighted its short corn in large party tents surrounded by corn plants. Salesmen in black jeans and white company shirts pitched VITALA as a package, combined with agronomic advice and digital maps based on satellite imagery and data streams from the farmers’ high-tech tractors and combines. The combination of technology and improved seed can push yields to 16 tons of corn per hectare, Bayer says, compared with the 12 tons typical for Sinaloa. Bayer expects about 6000 hectares of VITALA short corn to be planted in Sinaloa next year.

Whether conventionally bred or genetically engineered, short corn has other advantages, says Fred Below, a crop physiologist at the University of Illinois Urbana-Champaign, who has received funding from Bayer to study its new hybrids. Because the plant puts fewer resources into its stalk, it can divert more into roots—though Vyn notes that the extent to which this actually happens hasn’t been fully studied. A more developed root system would help plants better tolerate drought and extract fertilizer from the soil.

In U.S. field trials, the short corn benefited from nitrogen applied later in the season when it would be harder to add to tall corn, Vyn, Below and colleagues reported in Field Crops Research in May. That could have environmental benefits. Scientists have reported that water quality near farm fields can improve 15% to 20% when some of the fertilizer is applied later in the season. That’s when corn plants are enlarging their kernels and need it most, reducing the excess that can leach into groundwater or run off into streams. Excess nitrogen pollutes groundwater and causes algal blooms in lakes—even as far away from the Corn Belt as the Gulf of Mexico. Making better use of nitrogen fertilizer may turn out to be the biggest benefit of short corn, says Kendall Lamkey, a corn breeder at Iowa State University.

Additional environmental benefits could accrue if short stature allows farmers to spray fungicides on mature corn plants from tractors rather than airplanes, which can lead to greater drift away from the fields, potentially exposing people and wildlife. Although downsides may yet materialize, Below says he’s optimistic about the potential: “I’m convinced it’s going to be more advantages than disadvantages.”

FOR U.S. FARMERS, the prospect of greater yield may be the biggest lure. Stine Seed, based in Iowa, already sells short corn in the United States. Its varieties are not planted on a large scale, in part because Stine is a relatively small producer of corn seed. But Stine says its hybrids can exceed the yield of tall corn by up to 10% in optimal conditions.

Founder Harry Stine grew up on a small Iowa farm and started breeding corn and soybeans in the 1970s. Larger companies like Monsanto licensed the improvements he made in soybeans, making Harry Stine a fortune; now in his early 80s, he is Iowa’s only billionaire.

In the company’s early days, however, Stine had far less to spend on R&D than the big seed companies. That cost-cutting led to an unintended breakthrough with corn. The standard practice with breeding trials was to plant corn densely, then thin the plots to give plants room to grow. Stine didn’t have the labor to do this weeding, so he let all the plants live, then selected the corn from the plots that performed the best.

Over the years, this led to hybrids that were about one-third shorter than conventional corn. Their leaves are angled upward more, and the tassels are smaller, letting more light reach the lower leaves. Crucially, this means more plants can be grown per hectare, potentially increasing the overall harvest. “I think Harry’s onto something,” Lamkey says.

On his family farm in north-central Illinois, Darron Judd has been growing Stine’s short corn for several years. To get the recommended density in his fields, he had to modify his tractor to plant seeds in rows 38 centimeters apart rather than the standard 76 centimeters. The change was costly, but Judd likes the sturdiness of the short corn. “It just stands great.” He aims for 18 tons per hectare. The Illinois average is 13 tons.

Yet Stine Seed President Myron Stine says several factors have made it hard to win new customers for short corn. For example, farmers like to compare new varieties to what they’re used to growing, he says. If they do this by alternating rows of short and tall corn, the shorter hybrid will not perform as well because it’s shaded by the taller corn. Lamkey says another reason many farmers have been reluctant to plant corn more densely is that it forces them to bet on the weather: in a dry year, plants packed into a rain-fed field can literally run out of water. And Seth Murray, a corn geneticist and breeder at Texas A&M University, notes that farmers have to buy more seed to plant densely—offsetting some of the profit from higher yield.

For Bayer and Corteva, those hurdles may prove less daunting. Those two companies account for 70% of the U.S. corn seed market, and they have more resources to promote proper planting of short corn.

In Iowa, at least, they expect to find receptive ground. Farmers there have become “hyperfocused” on the risk of derechos, Lamkey says. Those who turn to short corn to reduce the risk of loss may reap other benefits, in yield and environmental protection.

Decades after wheat and rice were transformed in the Green Revolution, corn is getting its turn.

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