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Scientists have developed an effective form of biological control for a toxin-producing fungus that plagues crops in sub-Saharan Africa and poses serious a health risk to humans.

Scientists — from the International Institute of Tropical Agriculture (IITA) in Nigeria, the United States Department of Agriculture and three universities in Germany, Nigeria and the United States — have discovered a means of drastically reducing the amount of the fungus Aspergillus that produces a toxic substance called aflatoxin in maize crops.

The method uses benign forms of the same type of fungus to outcompete it.

The fungus Aspergillus grows on maize, an important cereal in African diets, as well as on groundnut, rice, sorghum and peanuts.

Millions of people in sub-Saharan Africa are exposed to aflatoxin through food. Long-term exposure to the toxin can result in liver cancer, immune suppression — making people more vulnerable to disease — and developmental and growth problems in young children. Cattle that eat contaminated feed can also become sick.

Farmers in sub-Saharan Africa lose about 40 per cent of their food crops to the fungus, and many maize-importing countries have strict controls on the level of aflatoxin they will accept, reducing grain exports.

The researchers collected 2,127 samples of Aspergillus, 1,000 of which proved to be non-toxin producing. They narrowed down their sample to just eight strains that were tested in both the laboratory and field.

"Our approach was to identify non-toxin producing strains that could competitively displace the toxin producing strains from the grains," explains Ranajit Bandyopadhyay, a plant pathologist with IITA .

The researchers found that when they applied both toxin and non-toxin producing types of Aspergillus to soil, which then spread to maize crops growing in the field, the levels of aflatoxin in these crops was reduced by up to 99.8 per cent.

The researchers intend to test the efficacy of the strains in a larger scale across Nigeria, with results due in late 2007.

Nigerian farmer, Samuel Ogunfolaji, says, "Many methods have been introduced in the past without much success. If this new approach will eliminate the disease, it will be a plus."

Peter Cotty, from the United States Department of Agriculture and a member of the research team, explained in a press release that using non-toxin producing strains that are indigenous to the area is crucial, because this ensures that the strains they release will be highly competitive under local conditions. They also pose less of an ecological risk compared with imported strains.

Samson Ayanlaja, a plant scientist at Nigeria's Olabisi Onabanjo University, told SciDev.Net, that he approved of the team's approach, "because it does not entail the use of chemicals that can pollute the environment. It is environmentally friendly."