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Corn+Soybean Digest

Soybean Gene Stops Afl atoxin

Soybeans may do more for corn than serve as a good rotation partner.

Laboratory studies by Nancy Keller, Texas A&M University plant pathologist, have shown that the product of a particular soybean gene inhibits aflatoxin production.

She's collaborating with Pioneer Hi-Bred International to put this soybean gene into corn to determine if the gene can reduce aflatoxin production in the field.

The end result could be aflatoxin-resistant seed corn available to farmers within three or more years, says Keller.

"That's extremely good news," says Carl Hensz, a Harlingen, TX, grower who saw much of his corn victimized by aflatoxin in last year's drought and in previous years.

"Aflatoxin-resistant corn would make a huge difference for my production," Hensz adds. "I'd feel much more comfortable planting corn instead of cotton."

Keller's research is part of a national war on aflatoxin by various scientists. This deadly toxin is caused by the fungus Aspergillus flavus. The fungus normally occurs when temperatures are 80-100 degrees, relative humidity is 62-99%, and kernel moisture content is 13-20%. Drought, accompanied by high humidity, is a major factor.

Keller's research began in the early '90s, with partial funding from the Texas Corn Producers Board, Pioneer Hi-Bred and other sources.

"Everyone's always known that, for some reason, soybeans are resistant to aflatoxin," Keller points out. "We were able to identify a soybean gene product that reduced aflatoxin production in lab settings."

She doesn't know if it's the same gene that gives soybeans their resistance, but it looks promising as an anti-aflatoxin gene in corn.

Keller's latest lab and field studies are to identify resistant corn lines.

"Pioneer transferred the gene into several corn lines," she reports. "We expect field tests to tell us which kernels inherited the soybean gene. We will then look at that line in 1999 or 2000, depending on which transgenic corn lines are ready. If it proves to be fully resistant, it will likely be released to commercial breeders."

Keller and her associates are also examining infected corn lines to determine exactly what in the ear or kernel induces aflatoxin.

"We hope to find out which corn compounds induce the fungus to produce aflatoxin, then determine how to turn it on and off," she says.

Don White, a University of Illinois plant pathologist, has been doing Corn Belt aflatoxin research since 1990. He first evaluated about 1,200 inbreds.

"We used an inoculation technique developed at the University of Illinois to select 33 highly resistant inbreds," White reports. "We narrowed it down to 11.

"We're trying to cross the resistant lines with sources of Corn Belt germplasm. We want to move the resistant genes into white and yellow lines that have good agronomic characteristics," White adds.

"We have identified different mechanisms of resistance more than likely controlled by different genes. It may be necessary to cross all of these genes into a single variety to have a high level of resistance."

Corn kernels in storage can become more susceptible to aflatoxin when invaded by maize weevils. ARS workers in Mississippi, Iowa and Kansas have discovered new corn lines with built-in weevil resistance.

"We're looking at commercial corn hybrids for resistance to the weevils in storage," says James Throne, an ARS researcher at Manhattan, KS. "Of 72 Pioneer lines, about one-third had some fair resistance. We're trying to find out the chemical or physical basis for that resistance and make it available to plant breeders."

Texas grower Hensz says there were few aflatoxin problems in the Rio Grande Valley in 1997. Cool, damp weather prevailed. The winter and early spring of '98 were also wet, but the region was in desperate need of water by late spring.

Then the infamous Texas drought, coupled with over a month of 100 degree-plus days, created a severe aflatoxin problem for many.

"There's always fear aflatoxin will come back," Hensz points out. "But hopefully we're doing a better job of managing the crop. And with the research we're seeing, we could be winning the battle."

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