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Dealing with drought

It is easy to see why corn-breeding companies are emphasizing drought tolerance. Just read some of last year's reports from the National Oceanic and Atmospheric Administration's National Climatic Data Center:

  • July 2007 brought record and near-record warmth to the western U.S. Below-average rainfall, combined with high temperatures, put 46% of the U.S. in some stage of drought by the end of July.

  • The June through August summer season ended with a long-lasting heat wave that produced more than 2,000 daily high temperature records across the southern and central U.S. At August's end, drought affected almost half of the U.S.

  • Temperatures in September 2007 were the eighth warmest on record, hot enough to break 1,000 daily high records.

According to Pioneer Hi-Bred International, drought stress is responsible for more lost bushels of corn yield than any other cause, costing American farmers as much as $3 billion annually.

Breeders and agronomists agree that water is the most limiting factor for corn producers. It is not surprising then that breeders have been selecting corn for drought tolerance for decades. More recently, they have been able to speed the process with marker-assisted selection and transgenic technology.

Pioneer uses conventional breeding, marker-assisted breeding and transgenics (incorporating genes from other species) in a coordinated approach, reports Jeff Schussler, Pioneer research scientist.

Its transgenic hybrids with drought-tolerance genes are still about five to seven years away, he says. But through genetic screening technology, Pioneer already has introduced some hybrids with native tolerance to drought.

Complex process

Breeding for drought tolerance is a complex process. Lack of water affects different parts of the corn plant (for example, roots, leaves and silks) at various stages throughout its growth. Breeders must accumulate genes that convey drought tolerance to these various plant parts simultaneously without adversely affecting yield, explains Mark Lawson, Monsanto's corn technology yield and stress lead. “Breeding is a slow process, but hopefully biotech will allow a step change,” he says.

Monsanto's biotech trait for drought tolerance in corn is in early development. “We have technology in the field and are collecting yield data,” Lawson says. “We'll decide this fall on the next steps to take.” The company could release hybrids with biotech-derived drought tolerance some time after the turn of the decade.

Monsanto's first-generation drought-tolerant hybrids will be targeted for the dryland market in the western Corn Belt, and its second-generation products will be aimed at broad-acre applications throughout the Corn Belt.

Water optimization

Enabling corn to use water more efficiently in both irrigated and dryland conditions is a centerpiece of corn development at Syngenta Seeds, says Wayne Fithian, the company's business lead product manager. Syngenta is using conventional breeding as well as gene sequencing, marker-assisted breeding and transgene technology to develop hybrids that optimize water.

“We're testing thousands of hybrids on both dryland and irrigated ground,” Fithian says. This includes test locations throughout the Corn Belt and particularly the West. Syngenta expects hybrids featuring its biotech-derived drought-tolerance genes to be commercialized sometime around the end of the decade. Syngenta's brands are NK Seed, Garst and Golden Harvest.

One of the company's goals is to stabilize yield potential in areas where it has been quite variable, such as in the western Corn Belt, Fithian says. The company's work also could allow corn to be grown in dry areas where it has not traditionally been grown. This is important as the demand for corn for both food and fuel continues to rise.

Growers in certain areas of the West who currently follow a wheat-fallow-wheat rotation could potentially switch to a wheat-corn-fallow rotation. This could help them better manage weeds and diseases affecting wheat production, Fithian says. He adds that university research has shown that breaking the wheat disease and wheat cycle (by introducing corn into the rotation) could help growers get as much as seven more bushels of wheat per acre.

Decades of progress

Hybridization and modern management practices also have helped improve drought tolerance and corn yields over the decades.

Paul Sun, vice president, research, Dairyland Seed, points out that in the 1930s, widespread drought occurred twice and only 85% of the corn was harvestable. With the introduction of double- and then single-cross corn hybrids, not only did yields climb, but at least 90% of the corn crop was harvestable after the long drought of 1988.

“We've been building drought tolerance over the years with conventional breeding. Hybridization has helped,” Sun says. Dairyland Seed has focused on conventional breeding, selecting hybrids that demonstrate high yield and consistency of yield year after year. “We cannot predict the weather, so stability is important,” Sun says.

He observes that high planting density tolerance also has an effect on drought tolerance, particularly in areas that experience periodic times of drought stress. In the 1930s, corn farmers planted an average of 8,000 plants per acre. Today, it is not unusual to see fields with 32,000 plants per acre.

Over the years, corn breeders have made significant genetic progress in yield gain in hybrid corn. Still, in the Corn Belt (with one crop per year), breeders face a fundamental challenge. Today's hybrids are not able to maximize use of all natural resources available to them during the growing season, Sun says.

Dairyland Seed's research program focuses on developing hybrids that will maximize use of all available natural resources during the growing season. “By taking this approach, we will secure yield gain as well as drought tolerance,” Sun explains.

Next year's weather patterns may be very different from those of 2007, but prolonged drought and periodic dry periods can happen at any time. Fortunately, work is being done to develop corn hybrids now and in the not-too-distant future that can better optimize water when it is there and survive when it is not.

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