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United States Department of Agriculture

Agricultural Research Service

Research Project: Chemical Approaches to Eliminate Fungal Contamination and Mycotoxin Production in Plant Products

Location: Foodborne Toxin Detection and Prevention

2012 Annual Report


1a.Objectives (from AD-416):
The overarching goal of this project is to develop methods to improve the safety of our food with regard to contamination by microbial toxins, mainly mycotoxins. In this regard, the project has a series of interconnected objectives. These objectives and their interrelationships are described as follows:

Objective 1: Develop detection methods for Volatile Organic Compounds (VOCs) to pinpoint food contaminants. Develop methods for identifying specific, "signature," volatile organic compounds (VOCs) as telltale indicators of microbial, mycotoxin contamination or insect infestation. This VOC detection will be applied to Objective 2. Objective 2: Develop methods for real-time detection of pathogen or insect contamination and toxins. Telltale VOCs will be used as real-time "signals" for detecting the presence of pathogens, mycotoxin-producing fungi or insects in crops or crop products, in post harvest storage or processing environments. This detectability will permit optimization of any intervention measures that are needed; which will be developed in Objective 3. Objective 3: Develop intervention technologies using plant VOCs / natural products as tools for the control of pathogens and insects. Specifically target the genetic control mechanisms through the use of chemosensitization and formulation development. Objective 4: Investigate the biochemical and genetic regulation of toxin production within fungal communities, with special emphasis on communication. Investigate the factors controlling aflatoxin catabolism and identification of the catabolic products.


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-throughput 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.


3.Progress Report:
This report documents progress for the parent Project 5325-42000-037-00D CHEMICAL APPROACHES TO ELIMINATE FUNGAL CONTAMINATION AND MYCOTOXIN PRODUCTION IN PLANT PRODUCTS which started February 2011.

This project is organized into four objectives, as follows:.
1)develop detection methodologies based on profiling volatile organic chemicals (VOCs) to identify and monitor food contaminants;.
2)develop technologies and instrumentation to detect pathogens, insects, or toxins based on the activities described in the first objective;.
3)identify and develop natural products to inhibit pathogens and insects directly or through chemosensitization;.
4)identify factors from other microorganisms that either promote mycotoxin production or degrade mycotoxins.

Substantial findings have been made over the past reporting period, with much of the research already published, or in press. These include identification and field-testing of volatiles as attractants to navel orangeworm. Identification of volatiles associated with fungal infection and aflatoxin contamination of almond. Identification of natural chemosensitizing agents using in vitro tests, then successfully testing them in in-vivo tests on plants. Several fungi were identified that have enzymatic capability of breaking down aflatoxin. But, also, some of these fungi, themselves, produce natural compounds that can be used as chemosensitizing agents to improve fungicide activity of commercial products.


4.Accomplishments
1. Improving the efficacy of commercial fungicides with natural products. Crop (agricultural) and human (medicine) fungal diseases are very difficult. Oftentimes the fungi are resistant to available antifungal agents and the antifungal agents are toxic to the environment or to the patient. ARS scientists at Albany, California, in collaboration with scientists at VNIIF, Russia, and IHMT, Portugal, are looking for new methods to improve agricultural fungicides and chemotherapeutic antifungal drugs, respectively. A number of safe, natural phenolic compounds were identified that synergize the activity of fungicides against a number of phytopathogenic fungi of barley and wheat (Russia) and antifungal drugs against human yeast pathogens, such as Candida sp. and Cryptococcus neoformans (Portugal). Both of these discoveries may have significant impact on improving wheat and barley production and for the chemotherapy of patients suffering from these diseases.

2. The almond-based host plant volatile blend reported last year is undergoing a second year of intensive field-trapping studies. Moreover, based on previous testing results and electroantennographic studies additional blends are being formulated and field tested for attractive behavior toward the navel orangeworm, the major insect pest to California tree nuts. The additional blends are based on host plant volatile emissions from both almonds and pistachios and various treatments of both (i.e., fungal contamination, damage). Results from the previous year attributed to the funding of a specialty crop block grant from the California Department of Food and Agriculture. The two-year award helps fund field trapping studies of the blend and additional formulations and comparison of efficacy to the current navel orangeworm monitoring standard, almond meal. Results thus far for the 2012 growing season confirm the blend’s ability to significantly attract more adult navel orangeworm moths than almond meal.

3. Improving the efficacy of commercial fungicides with natural products. Human fungal diseases are very difficult to treat and the fungi causing these diseases are often resistent to the antifungal drugs currently available. ARS scientists at Albany, California, are looking for new methods to improve antifungal drugs. ARS scientists in collaboration with Russian colleagues discovered that the culture filtrates of a fungus used in Russia as a biological control agent contains compounds that are effective chemosensitizing agents for the control of wheat and barley pathogens. Combining this filtrate with either azole or strobilurin type fungicides greatly improves the efficacy of the fungicides and prolongs their antifungal activity.

4. Innoculation of aspergilli and other orchard fungi. Scientists have performed intensive in vitro inoculation experiments of aspergilli and other common orchard fungi on almonds using almond fatty acids and proteins as the fungal media. Once completed, scientists will compare the emissions of various fungi relative to the volatile emissions of the orchard fungal bouquets to best determine the unique volatile emission pattern and/or emission ratios. A second objective is to determine which actual fungus is responsible for the unique volatile(s). Later this year, these results will be transferred to almond and pistachio media to determine the fungal candidate for inoculation.


Review Publications
Beck, J.J. 2012. Addressing the complexity and diversity of agricultural plant volatiles: a call for the integration of laboratory- and field-based analyses. Journal of Agricultural and Food Chemistry. 60(5):1153-1157.

Campbell, B.C., Chan, K.L., Kim, J.H. 2012. Chemosensitization as a means to augment commercial antifungal agents. Frontiers in Microbiology. 3:79.

Gee, W.S., Light, D.M., Beck, J.J. 2012. Electroantennogram bioassay as a screening tool for host plant volatiles. Journal of Visualized Experiments. 63:e3931.

Dragull, K.D., Beck, J.J. 2012. Isolation by ion-exchange methods. In Sarker S.D.; Lutfun, N. (eds) Natural Products Isolation, 3rd edition. New Jersey: The Humana Press Inc. Vol. 864:p.189-219.

Dzhavakhiya, V., Shcherbakova, L., Semina, J., Zhemchuzhina, N., Campbell, B.C. 2012. Chemosensitization of plant pathogenic fungi to agricultural fungicides. Frontiers in Microbiology. 3:87.

Kim, J.H., Chan, K.L., Faria, N.G., Campbell, B.C. 2012. Targeting the oxidative stress response system of fungi with safe, redox-potent chemosensitizing agents. Frontiers in Microbiology. 3:88.

Carruthers, R.I., Franc, M.K., Gee, W.S., Cosse, A.A., Grewell, B.J., Beck, J.J. 2011. Volatiles emissions from the flea beetle Altica litigata (Coleoptera: Chrysomelidae) associated with invasive Ludwigia hexapetala. Chemoecology. 21(4):253-259.

Last Modified: 10/23/2014
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