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Biopesticide on Tap Against Aflatoxin

Helping peanut farmers curtail fungi that contaminate their crop’s seed with aflatoxin is becoming a reality because of a biological pesticide developed by Agricultural Research Service scientists in Dawson, Ga.

The toxicity of aflatoxin, a fungal carcinogen, to humans and livestock makes it a costly problem for farmers, who lack direct means of controlling the fungi, and for peanut shellers once the seed has been harvested. By law, peanuts with more than 15 parts per billion of aflatoxin can’t be used in edible products. In Florida, Georgia and Alabama, aflatoxin outbreaks from 1993 to 1996 caused losses averaging $26 million annually. The main culprits, Aspergillus flavus and A. parasiticus, are fungi that occur naturally in soils.

Seeking a frontline defense against them, microbiologist Joe Dorner and his ARS colleagues turned their attention to nature. There, they identified benign, or nontoxigenic, strains of Aspergillus that compete with the aflatoxin-producing fungi for space and resources both need in order to grow.

Over the past 14 years, Dorner and other scientists at ARS’ National Peanut Research Laboratory in Dawson perfected methods of growing, formulating and applying the beneficial Aspergillus spores. Their approach, called bio-competitive exclusion, involves “seeding” these formulated spores around the base of peanut plants. There, by colonizing soils in the peanut pod zone, the mold becomes a living shield that blocks the aflatoxin-producing fungi.

In recent field tests, applying the formulation at a rate of 20 pounds per acre reduced aflatoxin levels by 70 to 90 percent versus untreated, control plots, Dorner reports.

Circle One Global, Inc., of Cuthbert, GA, has applied for an exclusive license on the biopesticide, and the Dawson lab is helping the company test commercial-scale methods of producing it.

A more detailed article appears in this month’s issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.