Submitted to: Peanut Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/1/2008
Publication Date: 4/30/2009
Citation: Dorner, J.W. 2009. Development of Biocontrol Technology to Manage Aflatoxin Contamination in Peanuts. Peanut Science. v.36 pp 60-67. Interpretive Summary: Aflatoxins are toxic, carcinogenic chemicals produced by the molds, Aspergillus flavus and A. parasiticus. Under certain conditions, these molds can grow in peanuts and other commodities, contaminating them with aflatoxin. Because this compromises their safety to be used as food, the quantity of aflatoxin in peanuts is closely monitored and regulated. Shelled lots of peanuts containing above the regulatory limit of aflatoxin cannot be sold for food use and must be crushed for oil. This compromises the economic viability of all segments of the peanut industry. Historically, the only way to prevent preharvest aflatoxin contamination of peanuts was to make sure they were adequately irrigated, particularly late in the growing season. However, the majority of peanut growers do not have access to irrigation, and with the frequent occurrence of late-season drought in areas where peanuts are produced, the result has often been unacceptably high levels of aflatoxin. We hypothesized that one way to prevent much of the contamination that occurs would be to inoculate soil with nontoxin-producing strains of A. flavus and A. parasiticus. Theoretically, these strains would out-compete the toxin-producing strains when peanuts are susceptible to infection, resulting in reduced levels of aflatoxin. This is a form of biological control called competitive exclusion. A series of studies was conducted over several years to develop and refine this technology. The first experiments confirmed the hypothesis. Further studies were carried out to determine the best nontoxigenic strain to use, the optimum inoculum rate, the effect on storage contamination, the best formulation to deliver the competitive mold to the field, and the safety of the mold and biocontrol product. After final development, the biopesticide was tested in large-scale field studies that demonstrated highly significant reductions in aflatoxin. The product was licensed by a commercial company and it received registration from EPA for use as a biopesticide in peanuts.
Technical Abstract: Aflatoxin contamination of peanuts results from invasion and growth of the fungi, Aspergillus flavus and A. parasiticus. Peanut pods develop in the soil where they are in contact with propagules of these ubiquitous fungi. When peanuts are subjected to drought conditions as pods are maturing, they become susceptible to contamination. A method of biological control of aflatoxin contamination was developed in which a competitive, nontoxigenic strain of A. flavus is applied to the soil to competitively exclude the toxigenic strains in the invasion of peanuts. The biocontrol product is comprised of conidia of the nontoxigenic strain coated onto the surface of hulled barley, which is applied to peanut fields during the middle of the growing season. After uptake of moisture the conidia germinate, grow, and sporulate, yielding a dominant population of the nontoxigenic strain in the soil. A variety of plot and field studies showed that aflatoxin in farmers= stock peanuts was reduced by 80 to 90% with this technique. The patented technology was licensed by a company that markets the biocontrol product under the trade name, afla-guard7. In 2004 the U. S. Environmental Protection Agency issued a Section 3 registration for use of afla-guard7 to control aflatoxin contamination in peanuts. Analyses of peanuts from the first commercial use of afla-guard7 in various locations in Georgia and Alabama showed aflatoxin reductions averaging 85% in farmers= stock peanuts and as high as 98% in shelled stock.