It's being heralded as the next big breakthrough for corn: drought tolerance. Expect corn hybrids with the inherent ability to perform where hybrids only a few generations ago would fail.

But mention drought trait, and its meaning — and value — can depend on where you farm, how you farm and even how Mother Nature treats you from year to year.

The intricacy of the drought-stress trait complex has made chasing the next step-change in corn hybrids somewhat elusive. But researchers are getting closer, and the first generation of these hybrids is expected to be on-farm in the next couple of years, with full rollout expected by the end of the next decade.

Drought tolerance is one component of stress tolerance that corn breeders and researchers have used to select corn hybrids for decades. “Corn breeding programs select hybrids each year based on their performance under prevailing growing conditions,” notes Mike Lee, professor of plant breeding and genetics at Iowa State University. “So each season there is a selection for drought tolerance. That will always go on.”

What has changed is that now corn researchers can identify specific genes or DNA sequences that have a documented effect on a plant's response to water stress. “The work now is to identify those genes, know their function and then try to introduce those genes that will carry out those functions in the corn plant.”

Sounds easy enough, but consider that there are about 50,000 genes in a corn plant, each with a very specific function that researchers are just beginning to understand. “Through its development, the corn plant has been very adept at collecting genes it finds useful,” says William Beavis, professor of population and quantitative genetics at Iowa State University. “So we have a database of a bunch of genes, and some may or may not have something to do with drought stress. We are learning, but right now we are just beginning to understand the interrelationships among all the genes.”

Drought, depending on its severity or duration, can impact a corn plant in different ways. There are the long-term dry weather patterns that can impact an entire growing season, and then there are the intermittent dry periods within key periods of the growing season. Specific corn hybrids will react differently to those stresses.

“With drought tolerance, it's important to define the target,” says Rita Mumm, director of the Illinois Plant Breeding Center at the University of Illinois. “There are many modes of action that can confer the stress tolerance. And it depends of whether you are targeting Corn Belt acres to provide some minimization of risk during pollination, or dryland corn areas where the water stresses are much different.”

THERE ARE TWO major categories in drought-trait research: improving the plant's ability to capture available resources, and modifying the plant to produce more grain with a finite amount of resources.

For instance, changing a corn hybrid's root structure to give the plant the ability to better capture available water would be one way to develop drought traits. On the other end of the spectrum would be modification of the plant's biochemistry to better utilize the amount of water available, making the most grain with limited resources.

So researchers look at all aspects of a plant's growth: root structure, leaf architecture, root mass, silking, pollination, to name a few — all to identify those areas that can have the most impact when water is at a premium.

One of the lower-hanging fruits of this effort is what's called anthesis to silking interval (ASI). In layman's terms: silks that don't properly form due to drought stress, ears don't fully pollinate and yield is reduced. “ASI has been well studied and is a known reason for reducing corn yields during drought stress at pollination, and is one of the first major flaws expressed when a hybrid is under stress,” says Jeff Schussler, senior research manager at Pioneer. “If silking is delayed, fewer kernels are pollinated. If we can modify the plant to better handle that stress, we should be able to improve silk emergence under stress.”

There's a lot of genetic variation in ASI, with some hybrids better able to handle this specific stress. And researchers are looking at current genetics as well as transgenic solutions that will help lead to the drought stress trait.

“The solution to drought stress isn't a silver bullet, it's more like silver buckshot,” says Mark Lawson, Monsanto yield and stress platform lead. “There are many avenues to reduce drought stress, and our goal is to find the ones that work best for the producer.”

Monsanto has completed its regulatory submissions in the U.S. and Canada for what it calls the world's first biotech drought-tolerant corn product. Developed with BASF, hybrids with this first-generation trait will target dryland corn producers in the western U.S. “This is a specific trait for areas with annual rainfall averages in the 12-16-in. range,” Lawson says. “We are targeting the approximately 10 million acres with a typical yield of 70-130 bu./acre.” Expected release, pending regulatory approval, is 2012.

Pioneer's first generation of drought trait hybrids is in final evaluations, and is expected by 2011. And Syngenta expects its entry into the drought trait arena will come by 2012.

WHY THE WEST FIRST? Basically,a drought-specific trait is easier to identify in more arid environments. Here again is one of the complexities of the drought trait: identifying what works well in a dry environment is relatively straightforward. Yet a hybrid that withstands a dry period may not be the best hybrid during normal growing conditions.

“Just because one gene is found to provide drought tolerance doesn't mean there aren't other adverse effects on the plant,” Lee says. “Once a gene is discovered, we have to go about testing in other environments to ensure the trait works as intended.”

In some situations, a drought-tolerant hybrid in central Iowa may actually under-perform in good, even marginal, growing conditions. “Targeted drought breeding has its strengths and limitations. We can find those that perform when under water stress, but we must ensure there are no yield penalties to the producer in optimum environments,” Schussler says.

So what can producers expect when drought stress traits become widespread? Company officials indicate that at a minimum, researchers plan for a 6-10% yield increase over current hybrids. That may be easier said than done. In the central Corn Belt, ever-improving corn hybrids are making that a moving yield target. “In years without drought stress, producers will see yield parity with our drought products. But in years where there is drought, they will see improved yields,” Lawson says. “Farmers need assurance that with the drought-stress trait there is improved yield stability and no negative effect.”

And it's likely that depending on the success of the drought trait, we could see expanding corn acres. “Producers in marginal growing areas are always trying to figure out ways to minimize the risk they have of growing a crop and would like hybrids that offered more stable yields,” Lawson says. “If we can provide hybrids that provide that improved yield stability, then farmers will have more options in their operations and one of those options might be a shift to more corn.”

How much will this cost? Companies interviewed say it's still too early to put a price on the technology. “We're still early in the process, talking with farmers understanding what type of value this technology can deliver,” says Steve Knodle, U.S. traits marketing manager at Monsanto. “We are looking at the results and the different benefits these traits will bring to farmers. We expect these traits to be stacked with our newest trait platforms and priced to deliver value to the farmer in those targeted geographies.”