2007 Annual Report
Aflatoxin contamination of agricultural crops, such as corn, tree nuts, peanuts and cotton seed, can result in serious economic losses on an annual basis. One approach that shows some promise of success in controlling contamination is use of other microbes as biological control agents against aflatoxin producing fungi. The discovery of any isolates that show promise as biocontrol agents could be fruitful for future biocontrol programs. Strains of the bacteria Pseudomonas chlororaphis and Pseudomonas fluorescens were discovered that reduced aflatoxin producing fungi by 10 to 100 fold in soil from corn fields. Experiments conducted by scientist in the Mycotonins Research Unit in Albany for 16 days, demonstrating persistence of bacterial populations and the extent of the resulting biocontrol. Above accomplishment falls under National Program 108 (Food Safety), Component, 2.1.5 (Biocontrol) Following growth of fungi that normally produce aflatoxin in this soil for 16 days, with or without bacterial co-inoculation, there was no extractable aflatoxin present, suggesting that environmental and nutritional conditions in this soil were not conducive to aflatoxin production. Experiment conducted by scientist in thr Mycotonins Research Unit in Albany CA in collaboration with ARS scientist in Stoneville, MS for field trials on corn. Above accomplishment falls under National Program 108 (Food Safety), Component, 2.1.5 (Biocontrol)
Field Trials Using a Safe Yeast Shows Promise for the Biological Control of Aflatoxin Producing Fungi. Aflatoxin contamination of agricultural crops, such as corn, tree nuts, peanuts and cotton seed, can result in serious economic losses on an annual basis. One approach that shows some promise of success in controlling contamination is use of other microbes as biological control agents against aflatoxin producing fungi. A few years ago, USDA scientists in the Plant Myctoxin Research Unit, Albany, CA, discovered a natural, safe yeast, Pichia anomala, that showed promise in lab experiments as a potential biological control agent. Large scale field tests using the yeast were conducted in 2005 and 2006 resulted in significant reductions in cluster loss and significant increases in harvestable yield of pistachios, and the yield for the yeast treatment was 12% greater than for the control. The yeast also effectively controlled a waterborne bacterial contaminant, and may be useful as a control measure against human pathogenic bacterial contaminants in the field. Genetic experiments also showed that the yeasts caused a reduction in the activity of genes involved in aflatoxin biosynthesis (omtA, O-methyltransferase A; omtB, O-methyltransferase B; aflR, aflatoxin biosynthesis regulator; and aflJ, adjacent to aflR). This research shows that this yeast may be a promising biological approach to controlling aflatoxin producing fungi directly on pistachios, without harming the quality of the harvested nuts. Above accomplishment falls under National Program 108 (Food Safety), Component, 2.1.5 (Biocontrol)
Use of Natural Chemical Lures and Viruses to Control Insect Pests of Tree Nuts. Insect feeding damage results in significant losses in harvest to the tree nut industries and impact plant health resulting from insect feeding which causes wounds in the protective layers surrounding nut kernels that allows infection by microbes, including fungi that produce aflatoxin. Aflatoxin contamination of foods is a significant food safety issue and USDA scientists in the Plant Mycotoxin Research Unit, Albany, CA, are finding ways of controlling these insect pests by using natural chemical lures that the insects use to find the nuts. By combining these lures with pesticides or specific insect viruses, these pest insects can be controlled effectively without contaminating the environment or inadvertently having harmful effects on non-pest organisms. Chemists within the unit are using instruments that can detect different chemical compounds from the host-plant while simultaneously measuring how the insects respond to the chemical by focusing on the navel orangeworm, (NOW), the most significant insect pest to the almond and pistachio and codling moth (CM), the most significant insect pest to walnut. To date, a virus has been discovered that is effective for control of both CM and NOW, in addition to use of a discovered lure to CM in combination with pesticides that has been found to be quite effective in the control of CM. Above accomplishment falls under National Program 108 (Food Safety), Component, 2.1.5 (Biocontrol).
Chang, P.-K., Hua, S.S.T. 2007. Nonaflatoxigenic Aspergillus flavus TX9-8 Competitively Prevents Aflatoxin Accumulation by A. flavus Isolates of Large and Small Sclerotial Morphotypes. International Journal of Food Microbiology. 114:275-279.
Chang, P.-K., Hua, S.T. 2007. Molasses Supplementation Promotes Conidiation but Suppresses Aflatoxin Production by Small Sclerotial Aspergillus flavus. Letters in Applied Microbiology. 44(2):131-137.
Hua, S.T., Tarun, A.S., Pandey, S.N., Chang, L.Y., Chang, P. 2007. Characterization of AFLAV, a Tfl/Sushi retrotransposon from Aspergillus flavus. Mycopathologia. 163(2):97-104.
Bayman, P., Baker, J.L. 2006. Ochratoxins: a global perspective. Mycopathologia. the Netherlands: Kluwer Academic Publishers 162: 215-223