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United States Department of Agriculture

Agricultural Research Service

Research Project: MOLECULAR AND GENETIC APPROACHES TO SUPPRESSING FUNGAL PATHOGENS AND MYCOTOXIN CONTAMINATION

Location: Foodborne Toxin Detection and Prevention

2007 Annual Report


1a.Objectives (from AD-416)
Objectives of the research .
1)Release a promising insect resistant, premium quality almond variety, and evaluate other advanced breeding selections..
2)Characterize almond seed coat tannins at the genetic and biochemical levels and examine associaion of specific antioxidants with seed coat ink staining..
3)Identify and integrate multiple resistances into regionally adapted, high commercial quality breeding selections. Reduce mycotoxin contamination of agricultural commodities focusing on tree nuts (almonds, pistachios and walnuts) by identifying natural constituents or biocompetitive organisms that inhibit growth of fungi and aflatoxin production. Identify target genes in fungi that trigger mycotoxin biosynthesis focusing on stress response pathways.


1b.Approach (from AD-416)
Identify the natural constituents responsible for resistance of certain varieties of tree nuts to growth of aflatoxigenic strains of aspergillus. Isolate and identify novel metabolites in sclerotia of Aspergillus and develop analytical methods for such compounds in order to assess exposure levels of tree nut orchards to the fungus. Identify genes involved in triggering mycotoxin biosynthesis using high-through put bioassays. Assays involve use of deletion mutants, gene knockouts and complementation analysis. Discover natural compounds that disrupt functionality of gene targets identified. Develop biosensors for detecting toxic fungi in pre- and post harvest environments.


4.Accomplishments
Identification of Genetic Basis of Inhibiting Aflatoxin Production using Natural Compounds. Aflatoxin is a highly carcinogenic compound produced by certain fungi that can infect a wide variety of edible agricultural products, such as peanuts, corn, tree nuts, and in some countries, wheat. Aflatoxin contamination is a major food safety issue and is strictly regulated, resulting in it also being a significant international trade issue involving US agricultural products. USDA scientists in the Plant Mycotoxin Research Unit, Albany, CA, in collaboration with scientists in the Food and Feed Safety Research Unit, New Orleans, LA were able to identify the genes that suppress aflatoxin biosynthesis. This was done using certain, new genetic tools that allows scientists to see what genes are “turned on” or “turned off” in an organism under different treatments. The USDA scientists grew fungi treated with antioxidant, natural compounds that suppress aflatoxin production and showed that certain genes that are involved in producing enzymes that degrade fats that have changed their chemical nature as a result of exposure to oxygen stress, results in the complete “turning off” of the genes that make aflatoxin. This finding is a major breakthrough in attempts to solve the aflatoxin contamination problem and expected to lead to identification of natural compounds in crop plants that can be augmented through breeding and suppress aflatoxin production. Accomplishment falls under National Program 108 (Food Safety), Component, 2.1.4.

Use of Safe Natural Compounds to Enhance Antifungal Activity of Commercial Fungicides and Antifungal Drugs. Fungal infection of crop plants poses a major problem to agricultural productivity, quality of agricultural products and food safety resulting from toxins that certain fungi produce. Additonally, there a certain fungi that are significant human pathogens, whose infection can lead to serious debilitation or death. USDA scientists in the Plant Mycotoxin Research Unit, Albany, CA have identified a number of safe, natural products that can significantly enhance the effectiveness of commercial fungicides, such as strobilurin and fludioxonil. These natural compounds are used to weaken the ability of the fungi to build their cell walls or to respire normally. Once these fungi are weakened by this “chemo-sensitization” the commercial products are anywhere from 100 to 1000 fold more effective. In collaboration with scientists at the MD Anderson Cancer Center, University of Texas and the Institute of Hygiene and Tropical Medicine, Lisbon, Portugal, this process of chemo-sensitization was also found to be effective against a number of human pathogenic fungi, as well. In this case, a number of natural compounds were found that enabled the use of antifungal drugs, such as itraconazole or fluconazole, against strains that had become resistant to these drugs. The use of this chemo-sensitization has promising potential in agriculture and medicine to help reduce environmental impact and costs of using fungicides and preventing or overcoming resistance. Accomplishment falls under National Program 108 (Food Safety), Component, 2.1.4.

Discovery of Analogs of Ferulic Acid as Potent Antifungal Agents. Fungal infections of agricultural products has a major impact on production, food quality and safety. Use of commercial fungicides is expensive and has an impact on the environment. Moreover, fungal pathogens are continuously developing resistance to commercial fungicides. USDA Scientists in the Plant Mycotoxin Research Unit, Albany, CA, have found a number of chemical compounds related to the natural compound, ferulic acid, have significant fungicidal activity. Some of these compounds show commercial promise and the structures of the compounds help us to understand how they work against the fungus. Accomplishment falls under National Program 108 (Food Safety), Component, 2.1.4.

Natural Compounds Inhibit Production of the Fungal Toxin, Ochratoxin A. Ochratoxin A is a chemical made by a number of different fungi that can infect agricultural commodities such as, barley, grapes, coffee, dried fruit and nuts. It is carcinogenic and can damage the kidneys. As such, contamination by this toxin is a food safety issue, nationally and internationally. USDA scientists in the Plant Mycotoxin Research Unit, Albany, CA have identified a number of safe, natural compounds that prevent ochratoxin production. Augmentation of these compounds in food crops, through breeding, may help to lower or prevent ochratoxin contamination, improving the quality and safety of the product. Accomplishment falls under National Program 108 (Food Safety), Component, 2.1.4.


5.Significant Activities that Support Special Target Populations
None


6.Technology Transfer

Number of web sites managed1
Number of non-peer reviewed presentations and proceedings10
Number of newspaper articles and other presentations for non-science audiences3

Review Publications
Molyneux, R.J., Schieberle, P. 2007. Compound Identification: A journal of Agricultural and Food Chemistry Perspective. Journal of Agricultural and Food Chemistry. 55(12):4625-4629.

Lardner, R., Mahoney, N.E., Zanker, T., Molyneux, R.J., Scott, E. 2006. Secondary metabolite production by the fungal pathogen eutypa lata: analysis of extracts from grapevine cultures and detection of those metabolites in planta. Australian Journal of Grape and Wine Research. 12(2):107-114.

Yu, J., Cleveland, T.E., Wilkinson, J.R., Campbell, B.C., Kim, J.H., Kim, H.S., Bhatnagar, D., Payne, G.A., Nierman, W.C. 2006. Aspergillus flavus expressed sequence tags and microarray as tools in understanding aflatoxin biosynthesis. Mycotoxin Research. 22(1):16-21.

Lee, S., Campbell, B.C., Ok, Y., Kim, J., Park, B., Liu, N. 2005. Biochemical changes in dehydrogenase, hydroxylase and tyrosinase of a permethrin-resistant strain of housefly larvae, musca domestica l. Environmental Toxicology and Pharmacology.20(2):258-263.

Kim, J.H., Campbell, B.C., Mahoney, N.E., Chan, K.L., Molyneux, R.J., May, G.S. 2007. Enhancement of fludioxonil fungicidal activity by disrupting cellular glutathione homeostasis with 2,5-dihydroxybenzoic acid. Federation of European Microbiological Societies Microbiology Letters. 270(2):284290.

Beck, J.J., Chou, S. 2007. The Structural Diversity of Phthalides from the Apiaceae. Journal of Natural Products. 70(5):891-900.

Beck, J.J., Kim, J.H., Campbell, B.C., Chou, S. 2007. Fungicidal Activities of Dihydroferulic Acid Alkyl Ester Analogs. Journal of Natural Products. 70(5):779-782.

Kim, J.H., Campbell, B.C., Mahoney, N.E., Chan, K.L., Molyneux, R.J., May, G.S. 2007. Enhanced activity of strobilurin and fludioxonil by using berberine and phenolic compounds to target fungal antioxidative stress response. Letters in Applied Microbiology. 55:134-141.

Last Modified: 8/22/2014
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