Drought Tolerance

July 25, 2009 01:44 PM

Drought-tolerant varieties look alluring, particularly now, with water an increasing concern across the nation.

Syngenta, Pioneer Hi-Bred and Monsanto Company promise they will have genetic packages with drought tolerance on the market before long. This summer, Thomas Carter, a geneticist with the USDA–Agricultural Research Service in Raleigh, N.C., is releasing the first true drought-tolerant soybean variety, based on more than two decades of work.

We're all eager to see what scientists develop and how it works in the field. Any genetic boost that helps crops withstand dry weather conditions could be a great help. But the enhancement still won't make crop management any less important for farmers. Shooting for bigger corn yields with higher plant populations could complicate the situation, as well.

"You can't give up on managing a crop, especially when water is limited. The plant is still vulnerable. You can't just ignore that,” says Mark Westgate, Iowa State University professor of crop production and physiology.

"There's no magic bullet for making a bigger crop and using less water. Pushing corn population up increases the possibility of a bad response under stressful conditions,” he says.

Drought is just one of many yield-reducing stresses. Others range from temperature extremes and salinity to chemical exposure, insects, nematodes and disease pathogens. Harvesting top yields will still require properly managing all of these stresses. Plus, in many parts of the nation, irrigation management will remain a key component.

"We can't be complacent, saying we've got drought-tolerant genetics and we just put them out there and not irrigate. We can't do it and expect good yields,” Westgate says.

Root to kernel. New technology providing greater root protection will help, since healthy roots are the basis for everything taking place in the plant.
"Rapidly growing root tips produce a lot of cytokinin that tells the plant to grow,” Westgate says. "Anything that slows growth of the plant will depress its ability to make kernels. The corn ear is not the plant's big priority for growth. It fights with everything else going on. When the plant is stressed, the ear is the first to lose. If there's stress during flowering, that tells the flowers to slow down growth. It doesn't take much stress for this to happen.”

That's why making sure the corn plant gets adequate moisture at key times is so important.

"Think what irrigation does to root growth,” Westgate says. "What timing of irrigation do roots need to proliferate and grow fast? If you keep roots healthy, the plant responds very positively to that. Roots sense moisture stress first. The early phase of seed development is the expansion phase. That sets the limit for how much the kernel can ever weigh. When that size is set, you cannot make it much bigger. You can make it smaller with early water stress, which shortens the duration of filling.”

While Westgate applauds the new drought-tolerant genetic work, good irrigation management that gets water to the crop at crucial times will remain vital, he says.

"The No. 1 stress factor with corn is still water,” Westgate says.


You can e-mail Charles Johnson at cjohnson@farmjournal.com.


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