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Biological control: Researchers target aflatoxin in corn

If it works in peanuts and cotton, maybe it'll work as well in corn. That's the philosophy driving researchers to look at a biological means of controlling aflatoxin in corn.

“Over the last several years, I've been watching with real interest the work being done by Joe Dorner and the National Peanut Research Laboratory at Dawson, Ga.,” says Dewey Lee, University of Georgia Extension agronomist. “He has used a biological approach to reducing aflatoxin in peanuts. And this same type of research is being conducted on cotton in New Mexico, Arizona and Texas, where cottonseed is subject to aflatoxin infection.”

This and other research, says Lee, could offer a short-term approach to reducing aflatoxin in corn until aflatoxin-resistant hybrids become available sometime in the future.

Aflatoxin continues to be a concern for Southeastern corn producers, he says. “We have aflatoxin problems just about every year in Georgia corn — it's a major concern for our growers. Our current method or approach to reducing or managing aflatoxin has consisted of one thing — irrigation.

“Georgia corn growers have shifted their production to about 65 percent irrigation. They've done this by reducing their corn acreage in the state from about 1 million acres down to 300,000, and shifting the remaining acreage to irrigation,” says Lee.

Good management, he continues, also plays a role in managing aflatoxin in corn. “If you have the opportunity to harvest early, you will see a reduction in those aflatoxin levels. You'll see an increase if you let that corn dry down from 22 to 25 percent to 13 to 15 percent in the field. Part of good management is getting that corn out of the field at 22 to 25 percent moisture and drying it,” he says.

A later planting date also will have a positive effect on aflatoxin levels, notes Lee, because the corn is maturing during cooler parts of the summer, and aflatoxin thrives in warmer temperatures.

“But we typically see slightly lower yields in those later plantings, so that might not be the best management tool to use,” says the agronomist.

Hybrid selection also can be a tool for managing aflatoxin, says Lee. “The only way to really affect aflatoxin with hybrids is by selecting hybrids with avoidance characteristics, such as a tight husk and good grain quality. The seed companies have provided us with hybrids that have good grain quality, including resistance to ear rot. But there's no usable hybrid now that has genetic tolerance or resistance to aflatoxin.”

Lee says he expects to see more progress in the future — with partnerships between USDA, public institutions and industry — in developing hybrids that will grow well, produce high yields, and resist the development of mycotoxins.

“The industry has provided us with great yielding hybrids. We've seen great consolidation in the industry, and a number of regional companies are providing hybrids that will increase your value on a per-acre basis.

“But the reality of the situation is that Southern corn acreage — from Texas to Virginia — represents only about 7 percent of the total marketplace. So companies are focusing more on that 93 percent of the market. And mycotoxins really haven't been up on the radar screen for many years.”

Mycotoxin research, says Lee, is not the priority in the Midwest and Mid-South that it is in the Southeast.

The biological control of aflatoxin, explains Lee, involves the seeding of non-toxic strains of Aspergillus flavus — the soil-borne fungus that causes aflatoxin.

“Joe Dorner at the USDA National Peanut Research Lab has had extraordinary success at reducing the levels of aflatoxin in peanuts when this type of strain has been seeded or applied to the field. It also has been very effective at reducing aflatoxin in cottonseed in work done by USDA researchers in Arizona, New Mexico and Texas, with upwards of 90 to 98 percent control.”

These successes, says Lee, have led he and other researchers to look at using the same method in corn. “A colleague in Mississippi also has looked at this in corn for the past three years, and his results have been extremely encouraging.”

Mississippi researchers, he says, used two non-toxigenic strains. These are strains that do not produce aflatoxin as a by-product of their natural infection says Lee.

“In other words, Aspergillus flavus grows, feeds and lives, but there's no by-product in the mycotoxins. Their non-toxigenic strains — CT3 and K49 — have been very effective in competing with toxic strains.”

The material developed by the National Peanut Research Laboratory is being marketed as alfa-guard by Circle One Global, Inc., a Shellman, Ga., company.

The EPA reportedly notified the company in February that the product had passed the pre-screening. The company has leased a plant in Cuthbert, Ga., and plans to have it operating by the third week in April.

“Hopefully, we'll eventually see a registration in corn if it continues to work well in research.”

In his research, Lee is applying the non-toxigenic strains to sterilized barley seed, so it can be applied to the field. “Studies in peanuts have shown that about 20 pounds of this barley seed coated with the non-toxigenic strain is about the best competitive rate for peanuts. We took the same protocol in peanuts and applied it to corn at four Georgia sites.”

Planting dates ranged from March through mid-April, with corn planted either in peanut or cotton fields. The plots were dryland and were planted in susceptible hybrids, says Lee.

The results from this past year were encouraging, he says, and the research will continue this year. “This has proven effective in cotton and peanuts. It also has proven effective in corn in Mississippi. And we saw a significant response in Georgia this past year.

“It won't be a cure-all, but it possibly can be part of multi-system approach to reducing and eliminating aflatoxin in corn.”


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