Submitted to: Aflatoxin and Food Safety
Publication Type: Book / chapter
Publication Acceptance Date: 6/23/2005
Publication Date: 6/23/2005
Citation: Dorner, J.W. 2005. Biological control of aflatoxin contamination of crops. Aflatoxin and Food Safety. pp 333-352. Interpretive Summary: Aflatoxin contamination of crops compromises the safety of food and feed supplies and causes significant economic losses each year. Aflatoxin contamination can occur when crops are infected with aflatoxin-producing strains of Aspergillus flavus and A. parasiticus, molds that are relatively abundant in agricultural soils. One promising strategy to prevent aflatoxin contamination is biological control that is achieved by applying a strain of A. flavus to soil that cannot produce aflatoxin. When a competitive, nontoxigenic strain of A. flavus is applied to soil, it competitively excludes the toxigenic strains and preferentially infects the susceptible crop, such as peanuts. But even though the crop is infected, aflatoxin contamination does not result because the infecting strain cannot produce the toxin. Various formulations have been used to apply the nontoxigenic strain to soil, but the most cost-effective is a small grain, such as barley, coated with spores of the nontoxigenic strain. One such product has been given the trade name afla-guard®, and it is being marketed commercially for use on peanuts. Another product, Aspergillus flavus AF-36, is made by fermentation of the nontoxigenic strain on wheat, and it has been approved for use on cotton. Use of these products has produced significant reductions in aflatoxin contamination in peanuts and cottonseed.
Technical Abstract: Aflatoxin contamination of crops compromises the safety of food and feed supplies and causes significant economic losses each year. Of the many research approaches being studied to reduce and, ultimately, eliminate aflatoxin contamination, biological control is one of the more promising, particularly for the near-term. Numerous organisms have been tested for biological control of aflatoxin contamination including bacteria, yeasts, and nontoxigenic strains of the causal organisms, Aspergillus flavus and A. parasiticus. Most of the field successes to date have been achieved by applying certain nontoxigenic strains of A. flavus and A. parasiticus to soil of susceptible crops, such as peanuts, cotton, and corn. The applied strains occupy the same niche as the naturally-occurring toxigenic strains and competitively exclude them when crops are susceptible to infection. Various formulations have been used to apply the nontoxigenic strains to soil, but the most effective methods have been to combine the desired strain with a carrier/substrate, such as a small grain. This was done either by minimally growing the desired strain on sterilized grain or by coating the surface of the grain with conidia of the strain. After application to the field and uptake of moisture, the fungus completely colonizes the grain, and abundant sporulation provides inoculum levels sufficient to achieve a competitive advantage for the nontoxigenic strain. In several years of field studies, particularly with peanuts and cotton, significant reductions in aflatoxin contamination in the range of 70-90% have been achieved consistently.