A Maize Mutant

By Pam Smith
DTN Progressive Farmer Crops Technology Editor

LAWRENCE, Kan. (DTN) -- Most farmers cringe at the sight of an insect-ravaged corn plant, but the defoliated leaves of one corn plant signified a major breakthrough for researchers at Purdue and the University of Illinois.

Gurmukh Johal, a Purdue plant pathologist, and Stephen Moose, a University of Illinois plant scientist, discovered a mutant corn plant with leaves decimated by Western corn rootworm. Typically, this is a pest that costs corn growers more than $1 billion a year by feeding on roots and snacking on pollen and silks.

Occasionally, early emerging beetles will feed and scratch on corn leaves as they wait for silks to emerge. However, in the case of this newly discovered mutation, biochemical and physical changes in the corn leaves caused the rootworm to chow down.

"Up until the discovery of this mutant, people thought well, maybe there's nothing in the corn leaf that this beetle likes to eat," Johal told DTN. "But this mutant tells us that probably there's something in the corn leaf that prevents the beetle from eating it -- there's maybe an active mechanism that keeps this beetle typically from eating."

The discovery could give scientists and farmers new and much-needed information to battle Western corn rootworm. In recent years, the pesky insect has evolved some resistance to Bt traits and crop rotation in major corn-producing states like Iowa and Illinois.

Christian Krupke, a Purdue entomologist and co-author of the study, is testing methods to use these mutant plants to bait and move the beetles around cornfields.

"What we've found in the relatively small plots where we've worked is that the majority of the beetles there will concentrate on the mutant plants," Krupke told DTN. "That's certainly unprecedented and it's a real benefit." The beetles don't just like the corn leaves -- they love them, he added. "They stayed on those plants much longer, and in fact, they stayed on them until they defoliated them."

One concept being explored is that farmers could plant the mutant plants in field boundaries and lure the beetles in, Krupke explained. They could then plant that rootworm-infested area to soybeans the next year, killing the eggs in the soil and reducing the rootworm population over time. If rootworm variants with resistance to crop rotation are present, farmers could reduce populations by spraying the beetles in the heavily infested field borders before they laid eggs.

Such a simple, low-tech method could play a big role in future pest management strategies, Krupke believes.

"[Corn] is the largest crop in North America," he said. "If you have a way to move the largest single pest insect of the largest crop around, well that's something to pay attention to."

Further research could produce even more sophisticated tools. Johal's lab is working to clone and examine the gene in non-mutants that protects corn leaves from insect feeding. The idea is to make even tougher corn varieties.

"We could overexpress the gene or we can somehow express it in different parts of the plant in ways that will make the plant more resistant to the beetle," Johal said of his hopes for future research.

His lab has also discovered two other mutations that make corn leaves palatable to European corn borer and the fall armyworm. Johal said much of his research on those mutations is being done in collaboration with Pioneer.

The research on the original mutation was conducted with funding from Pioneer, the U.S. Department of Agriculture, and the Illinois Agricultural Experiment Station.

(PS/AG/CZ)

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