LSU researchers look for biological controls for aflatoxin

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Of all the issues farmers must contend with, aflatoxin-contaminated grain can be one of the most costly at harvest. Several strains of Aspergillus fungi produce aflatoxins, which are complex, harmful pathogens that attack several crops, including field corn. Louisiana State University AgCenter researchers are working to develop biological controls for these aflatoxin-producing fungi.

That is not a simple task, according to AgCenter plant pathologist Ken Damann. He has been studying ways to manage aflatoxins since 1998, when there was a severe outbreak in Louisiana.

"Aspergillus flavus is a soil-borne fungus that is ubiquitous," Damann said. "The fungus itself is not bad, but sometimes it makes secondary metabolites referred to as aflatoxins that have health concerns for people if consumed."

Some strains of the A. flavus fungus produce aflatoxins, but others do not. Those variances make aflatoxins difficult to understand, but they could also be key to control.

Damann said some strains of A. flavus are actually nontoxic and can stop toxic strains from producing aflatoxins when the two infect the same grain. While that mechanism represents promising potential for biological control, there are a few catches.

"Only certain nontoxic strains inhibit certain toxic ones," Damann said. "When we deploy nontoxic strains in the field, we need mixes of these strains of differing specificities."

To identify which strains effectively prevent the production of aflatoxins, Damann and Zhi-Yuan Chen, AgCenter plant biologist, are sorting through the multitude of A. flavus strains to determine which are the "bad guys."

Chen said some strains cause visible fungal growth on infected seeds but do not produce aflatoxins, while in other cases, there is no fungal growth but aflatoxins are still present.

Aflatoxins are a big concern for corn farmers, Chen said, because the FDA regulates how much aflatoxin can be in corn. If the concentrations are too much, the grain cannot be sold.

Damann said some aflatoxin-inhibiting strains work on field corn and not other plants, or vice-versa. Because aflatoxin contamination is such a major issue for corn, the strains used in potential biocontrols must be infectious in corn.

Damann is also looking at a bacterium found in rice that inhibits aflatoxins. Eventually, he said, it could be used in conjunction with nontoxic A. flavus strains in a spray to reduce aflatoxins in grain.

"We want to have not just one strain of these organisms for biocontrol, but multiple ones that cover the spectrum of damaging A. flavus strains in the field," Damann said.

Some of the funding for Damann and Chen's work comes through the Aflatoxin Mitigation Center for Excellence, which is administered by the National Corn Growers Association. Other funding is from the Louisiana Soybean and Grain Research and Promotion Board.

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