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Corn+Soybean Digest

STOP Aflatoxin Contamination

If you grow corn or cotton in the South, your fields have likely been attacked in one extreme or another by the aflatoxin-producing mold Aspergillus flavus. But Northern growers, too, won't soon forget the drought of 1988 that brought aflatoxin-contamination losses of more than $273 million to parts of the Corn Belt.

However, if aflatoxin research continues to produce the promising results emerging from USDA-Agricultural Research Service labs in New Orleans, there could be a Mardi Gras atmosphere for those farmers who have suffered from the devastating fungus.

Ridding corn and cotton of aflatoxin is the mission of Ed Cleveland and his colleagues at the Food & Feed Safety Research Unit at USDA's Southern Regional Research Center. The unit is a leading player in the nationwide aflatoxin control studies at 14 universities and USDA locations.

Aflatoxin contamination of crops continues to have no 100% remedy. It still diminishes the value of corn, cotton and other crops such as peanuts. Laws dictate that food and feed corn can contain no more than 20 parts aflatoxin per billion parts (ppb) of commodity. And even smaller readings have forced grain shipments to be rejected by buyers, especially for export. In only extreme cases of contamination, that number increases to 200 ppb for feed corn.

Infected crops must be blended with clean corn or cottonseed to reduce the ppb. Costly fumigation can also help relieve aflatoxin pressure. But these processes are approved only in a few states and cannot be used for interstate commerce, notes Cleveland, “so there's no easy way out.

“It's a chronic problem for many cotton areas and Southern corn production,” he says. “Our major research to rid us of the aflatoxin contamination problems involves three projects that attack the problem from the soil to the fungal cell.”

One program centers on aflatoxin in Arizona cotton, a crop that has long been impacted by invasions of the fungus. The region's hot, droughty conditions help breed the menace in the soil. ARS's Peter Cotty of the New Orleans station, working in Arizona in cooperation with the Arizona Cotton Growers, has discovered a non-toxic-producing relative to the aflatoxin-causing fungus.

Cotty inoculates killed wheat seed with the non-toxic material. The seed is then spread evenly on top of soil to be planted in cotton at a rate of 10 lbs/acre. The wheat seed applications cost about $5/acre. “The non-toxin fungus competes against its toxic counterpart within the soil,” says Cleveland. “The non-toxic strain has been strong enough to offset the development of aflatoxin. We have seen as high as 90% reduction of aflatoxin in this program.”

Cotty has expanded his studies to more than 20,000 Arizona cotton acres. He expects to increase production of the non-toxin material at the commercial level soon. He will also conduct additional tests to determine the most cost-effective application rate.

Cleveland says this process could also work in corn, adding that similar research is already under way in parts of south Texas where corn production has suffered from aflatoxin. But he sees development of aflatoxin-resistant corn varieties as the best long-term method of controlling the toxin. That is the second major initiative of his group.

“There are varieties of corn where some of the inbreds show good resistance to the growth of the fungus and the production of aflatoxin,” he says. “Using gene marker selection, we are working with plant breeders at Mississippi State University to move these traits into agronomically acceptable genetic backgrounds.

“We also hope to insert the genes for resistance against the fungus into corn and cotton varieties so that either the fungus is killed or the chemistry of aflatoxin production is interrupted.”

Establishing what the “on-and-off switch” is for aflatoxin production is a project headed by Deepak Bhatnagar. This area of research has deciphered the genetic mechanism of aflatoxin synthesis — the “master switch” for turning aflatoxin development on and off.

“We have identified almost all genes required by the fungus for aflatoxin production,” says Bhatnagar. “Now that we have identified the master switch, we must find out what turns it on and off … We want to know why Peter Cotty's strain (in Arizona) does not make the toxin.”

Within the resistant corn germplasm, Bhatnagar and his associates have found three types of proteins that can alter development and progression of the fungus, and consequently aflatoxin development. “One protein kills the growth (of the fungus),” says Bhatnagar. “A second affects the toxin without affecting the fungus. A third gives the plant the ability to protect itself from invasion of the fungus.”

This information “opened the door to gene insertion” of the anti-aflatoxin traits into cotton embryo and germinated into a fully developed plant, says Cleveland. “Since cotton has little resistance to aflatoxin as opposed to corn, we think the gene insertion process can take off and become the most preferred by plant breeders,” he says.

There's no magic bullet, however. Even though these research results are more promising than any previous studies, getting results from the laboratory to the producer's plants is a slow process.

Cleveland and his colleagues see at least another five years before producers can benefit directly from aflatoxin-resistant seed and other control measures. “Once we have thoroughly tested these processes and get them to commercial seed companies, it will likely take a combination of plant resistance and biocontrol methods to prevent aflatoxin problems,” he says.

Still, the results seen by the New Orleans-based research are major steps toward helping growers rid their crops of the profit-killing fungus.

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