| |
| Mycotoxin Research |
|
Overview
|
At NPRL we are concerned with mycotoxins, harmful chemicals produced by certain species of fungi. Under certain conditions, these fungi can infect and grow in various crops, including peanuts and corn, contaminating them with mycotoxins.
Because mycotoxin contamination threatens the safety of food and feed, extensive monitoring must be done to ensure that mycotoxins are below levels set by the Food and Drug Administration. The most important mycotoxin that may contaminate peanuts and corn is aflatoxin. Not only is aflatoxin contamination a food safety concern, it is a major economic problem for the peanut and corn industries, which have to pay for the monitoring and take other expensive steps to be sure that products going into the edible market are essentially aflatoxin-free.
| Aflatoxin represented by: |
|
 |
 |
|
TLC |
HPLC |
The NPRL has conducted research on aflatoxin contamination of peanuts for many years and has recently developed and patented technology for biological control of aflatoxin contamination. This technology has been licensed and commercialized by Circle One Global, Inc., under the trade name, afla-guard®. Since receiving EPA registration as a biopesticide in 2004, afla-guard has been used in commercial peanut production in the southeastern US where aflatoxin contamination is historically the highest. It is also being used in large-scale tests on corn under an EPA experimental use permit. If those trials prove to be safe and successful, it is expected that the label would be extended to include that crop as well.
For more information contact:
|
Biological Control of Aflatoxin
Aflatoxin contamination of peanuts is a food safety concern and major economic burden for the peanut industry.
Technology has been developed for biological control of aflatoxin contamination. A competitive, nontoxigenic strain of Aspergillus flavus is applied to soil where it displaces the strains that produce aflatoxin.
The biocontrol technology has been licensed by Circle One Global, Inc., which is selling the product under the trade name, afla-guard®. afla-guard® has been registered by EPA as a biopesticide for use on peanuts to control aflatoxin and has been used commercially since 2005.
| afla-guard®consists of hulled barley coated with spores of non-toxigenic A. flavus. |
 |
| afla-guard® is applied to peanut about 60 days after planting. |
 |
| Non-toxigenic A. flavus sporulates on the barley surface and inoculates soil. |
 |
» Aflatoxin Reduction from Biological Control
Studies over several years in the NPRL environmental control plot facility have shown consistent aflatoxin reductions in the range of 70-90%. Peanuts in field tests that were exposed to natural drought conditions in 1997, 1999, and 2002 also had aflatoxin reductions of ≥90% when treated with the competitive fungus.
|
Field Test Results
Aflatoxin (ppb) |
| Treatment |
1997 |
1999 |
2002 |
| Control |
603.5 |
516.8 |
88.7 |
| Treated |
50.8 |
54.1 |
1.4 |
| Reduction |
91.6% |
89.5% |
98.4% |
Treatment of peanuts in the field with the competitive fungus has a beneficial, carryover effect when peanuts go into storage. When field-treated and non-treated peanuts, which were not contaminated with aflatoxin, were stored under conditions that would favor contamination, aflatoxin levels in peanuts that had been field-treated were reduced by 98% compared with untreated peanuts.
|
Storage Test Results
Aflatoxin (ppb) |
|
Treatment |
Prestorage |
Poststorage |
|
Control |
0 |
78.0 |
|
Treated |
0 |
1.4 |
|
Reduction |
- |
98.2% |
» Commercial Results
afla-guard® was applied commercially for the first time in 2004 to about 5,000 acres of peanuts in Georgia and Alabama. Analyses of farmers' stock peanuts from 582 loads showed that afla-guard® reduced average aflatoxin by 85% and consistent reductions were seen in all areas. Analyses of shelled stock peanuts from 2 warehouses resulted in no lots from treated areas being rejected because of aflatoxin compared with rejection rates of 16 and 48%, respectively, for untreated peanuts.
|
Commercial Use Results
Aflatoxin (ppb) |
|
Untreated |
Treated |
| Farmers' Stock |
78.9 |
11.7 |
Shelled Stock
Warehouse 1 |
36.2 |
0.9 |
Shelled Stock
Warehouse 2 |
7.2 |
2.2 |
» Corn
In 2007 the EPA granted an experimental use permit to allow large-scale testing of afla-guard on corn. The study was conducted in two areas of Texas that normally experience extensive aflatoxin contamination. afla-guard® was applied at rates of 10 and 20 lb/ac to approximately 3000 acres, and corn from treated and control fields was evaluated for aflatoxin contamination. Weather conditions during the 2007 crop year in Texas were unusually wet and relatively cool, conditions that do not favor aflatoxin contamination. Even though aflatoxin levels were much lower than normal, they were significantly reduced in fields treated with afla-guard®. There was no difference between the two rates. Testing will be continued in 2008.
|
Field Results, Corn
Aflatoxin (ppb) |
|
Treatment |
Victoria Area |
Uvalde Area |
|
Control |
5.4 |
0.9 |
|
10 lb/ac |
0.5 |
0.3 |
|
20 lb/ac |
2.3 |
0.1 | |
For more information contact Joe Dorner.
|
Fungal Invasion of Peanuts
|
Peanuts fruit underground and are in direct contact with soil populations
of Aspergillus flavusand Aspergillus parasiticus, the two fungi responsible for producing aflatoxin in peanuts.
|
|
|
|
|
|
Aspergillus flavus
|
Aspergillus parasiticus
|
A laboratory procedure has been developed in which viable peanut seeds
are wounded and inoculated with soil directly from the field. This
research has shown that despite low spore densities in soil, aflatoxin-producing
fungi preferentially invade peanuts over other soil-inhabiting fungi.
Invasion is greatly influenced by seed moisture and soil temperature.
|
|
|
|
Seeds colonized by
Aspergillusspecies
|
|
Effect of soil population density on peanut infection
|
This procedure is currently being used to assay different nontoxigenic A. flavusstrains for their ability to reduce aflatoxin in biological control.
|
Ability of eight nontoxigenic Aspergillus flavusstrains to inhibit aflatoxin production by specific aflatoxin-producing
strains using the peanut seed assay
|
|
|
Nontoxigenic strains
|
| Aflatoxin production by strain F35
|
|
| Significant reduction of aflatoxin:
|
Strain A > B > C > D > E > F
|
| No significant reduction in aflatoxin:
|
Strain G, H
|
|
|
|
| Aflatoxin production by strain F14
|
|
| Significant reduction of aflatoxin:
|
Strain G > C > E > A > D > F> H > B
|
|
|
|
| Aflatoxin production by strain F86
|
|
| Significant reduction of aflatoxin:
|
Strain H > A > C
|
| No significant reduction in aflatoxin:
|
Strain B, E, D, G, F
|
|
|
|
| Aflatoxin production by strain F44
|
|
| Significant reduction of aflatoxin:
|
Strain C > A > D > G > E > F
|
| No significant reduction in aflatoxin:
|
Strain B, H
|
|
|
| F= Biological control strain in current use
|
For more information contact
Bruce Horn.
|
Fungal Population Biology
|
A thorough understanding of the ecology and population biology of aflatoxin-producing fungi is a prerequisite for devising new strategies for controlling aflatoxin in peanuts. We have examined populations at three spatial scales.
Single peanut field in Georgia: Population structure is complex and aflatoxin production by fungi is extremely variable.
 |
 |
|
Aflatoxin production by different genetic groups |
Transect through the southern United States: Peanut-growing regions having severe aflatoxin outbreaks are dominated by toxigenic strains of Aspergillus flavus.
Worldwide populations where peanuts are grown: On-going study in collaboration with North Carolina State University shows large differences in population structure and genetic composition.
(Map courtesy of CIA - The World Factbook)
For more information contact Bruce Horn.
|
|
|
|
|
