January 08, 2008

Biological Control of Aspergillus in Africa: I Have Questions

The history of biological control boasts numerous successes and numerous failures. Ladybugs are commonly used to control aphids to marked effect. At the other end of the spectrum, there have been disasters such as the introduction of cane toads into Australia in the effort to combat mice in grain fields. Today brings a report of an effort to control aflatoxin-yielding Aspergillus fungi in Nigeria by overwhelming them with native, non-toxic strains:

Scientists Find Way to Limit Deadly Toxin in Maize

Fears of poisoning by aflatoxin may soon be a thing of the past. The toxin affects many African staples and exports, including groundnuts and maize. Produce contaminated with aflatoxin can kill – and has resulted in a drop in the shipment of some African crops abroad.

But scientists have now found a way to destroy aflatoxin in maize. They say the same method could likely eliminate or reduce the toxin in groundnuts as well...

The method uses benign forms of the fungus to crowd out the toxic ones.

The researchers collected more than four thousand strains of Aspergillus – nearly one-fourth of which did not produce the toxin. In the end, scientists narrowed their testing to eight strains found in laboratories and in the fields.

They applied the benign samples with the toxic ones to the soil and found the benign strains were able to eliminate almost all of the toxic ones.

The next step is to test the results after releasing a number of strains in large-scale field trials at several sites in Nigeria.

Dr. Ranajit Bandyopadhyay is a plant pathologist with the International Institute of Tropical Agriculture, the IITA. He told the press, "The bio-control project is at an exciting stage, where we need to finally prove that the atoxigenic strains can drastically reduce aflatoxin contaminations in real farming situations in Africa..."

Peter Cotty is a leading scientist from the United States Department of Agriculture and a member of the research team on aflatoxin reduction in crops. He says it’s crucial to use non-toxin-producing but indigenous strains to ensure that the strains they release will be highly competitive under local conditions...
I haven't read any publication resulting from the studies, so I find myself left with some questions about how effective this approach would be outside of the laboratory.

For instance, if the non-toxic Aspergillus are also indigenous, why don't they already outcompete the toxic strains? It's a soil fungus, and I don't imagine that the researchers intend to dig up all of the soil on African farms, treat it to remove the toxic fungi and replace them with the non-toxic fungus. The non-pathogens aren't squeezing the nasties out of their niche in nature as things stand. Why would this situation change, and even if the environment were manipulated, what's to stop the harmful mold from making a return? How much does maintaining the favorable situation cost over time and how will the expense impact farmers and/or governments in Africa considering that they're already in a situation where their agricultural products are already restricted for export?

The press release doesn't delve into any of this because that's not what press releases generally do. They tend to play up one particular angle, so they make things sound great or terrible. The facts usually lie somewhere in between.

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