Submitted to: Aflatoxin Elimination Workshop Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 20, 2005
Publication Date: May 25, 2006
Citation: Dorner, J.W. 2006. Transfer of aflatoxin biocontrol technology: results of first commercial use in peanuts. Aflatoxin Elimination Workshop Proceedings. Interpretive Summary: None required for abstract only.
Technical Abstract: A method for biological control of aflatoxin contamination of peanuts has been developed through several years of research. Biological control is achieved by introducing a dominant population of a nontoxigenic strain of Aspergillus flavus into the soil of the growing peanut crop, and the applied strain competitively excludes toxigenic strains in the colonization of peanuts during periods of late-season drought. A significant accomplishment in the development of this technology was the development of a unique formulation technique in which conidia of the nontoxigenic strain are coated onto the surface of hulled barley, which serves as a carrier for delivery of the fungus to the field and also as a substrate for further proliferation of the fungus after application. ARS patents for this technology were licensed for commercialization in 2002, and the biocontrol product, afla-guard®, received EPA section 3 registration as a biopesticide in 2004. This made possible the first commercial use of the product on approximately 5000 acres of peanuts during crop year 2004 in southeastern Alabama and southwestern Georgia. To determine the efficacy of afla-guard® in large-scale use, soil samples from representative treated and untreated fields were dilution plated to determine A. flavus populations and toxigenicity. In addition, farmers’ stock peanut samples were collected at buying points in each area of use and analyzed for aflatoxin. Finally, treated and untreated peanuts that had been stored separately for several months were analyzed after shelling to determine aflatoxin in shelled lots prior to sale. Application of afla-guard® changed the composition of A. flavus soil populations from 71.1% toxigenic strains in untreated fields to only 4.0% in treated soils. Analyses of farmers’ stock peanuts being delivered at seven different locations showed a consistent reduction in aflatoxin contamination in peanuts from fields treated with afla-guard®. Over all locations, aflatoxin averaged 78.9 ppb in untreated peanuts compared with 11.7 ppb in treated peanuts, an 85.2% reduction. Peanuts from treated and untreated fields were stored together in separate warehouse bins at two different locations. Aflatoxin analyses at the Unadilla, GA location showed a mean aflatoxin concentration in all shelled edible lots from untreated fields of 36.2 ppb compared with a mean of 0.9 ppb in lots from treated fields. At the Dawson, GA storage location, aflatoxin means for shelled lots were 7.2 and 2.2 ppb for untreated and treated peanuts, respectively. For shelled lots to be sold to a manufacturer, an official aflatoxin analysis of the lot must show the lot to contain ' 15 ppb of aflatoxin. If the lot contains > 15 ppb, costly remilling and blanching must be carried out to try to reduce the level to 15 ppb or less. In analyses of shelled untreated lots from the Unadilla warehouse, 48.4% of those lots tested at >15 ppb compared with no such lots from the treated peanuts. At the Dawson location, 15.8% of shelled lots from untreated fields contained >15 ppb compared with no lots of treated peanuts. This translates to a reduction in net shelled stock value for untreated peanuts of 13.0 and 4.3% for Unadilla and Dawson, respectively. Using the European Union tolerance of 4 ppb for total aflatoxins, those reductions in value for untreated peanuts were 19.1 and 11.6%, respectively. Converting the value changes to a farmers’ stock ton basis, the differences in net farmers’ stock value for the peanuts stored in Unadilla were $51.55 and $72.78 per ton, respectively, for the 15 and 4 ppb tolerances. Equivalent differences for the Dawson peanuts were $11.33 and $39.18, respectively. These data illustrate the economic benefits that can be gained from use of the biocontrol agent to control aflatoxin in peanuts.