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United States Department of Agriculture

Agricultural Research Service

Research Project: DISCOVERY OF ANTIFUNGAL COMPOUNDS FROM LOW VALUE/UNDERUTILIZED CROPS AND CROP CO-PRODUCTS

Location: Food and Feed Safety Research

2010 Annual Report


1a.Objectives (from AD-416)
Enhance value and utilization of low value/underutilized crops and crop co-products through discovery and purification of novel, constituent antifungal compounds and determine commercial potential of discovered antifungals.


1b.Approach (from AD-416)
Barley and cotton 3-day old cotyledons will be extracted aqueously as will okra fruit and peanut and rice hulls. Filtered, freeze-dried extracts will be tested for fungicidal properties. Active compounds will be purified by HPLC/MS and activity monitored with bioassays using Aspergillus flavus and Fusarium oxysporum. NMR will determine chemical structure of antifungal compounds. Novel compounds will be patented and all active compounds will be tested for their antifungal spectra of activity. Commercial potential of compounds as agricultural fungicides and medical antifungals will be determined by collaborators. Discovered protein antifungals will be cloned. Construct genes will be incorporated into gene expression systems to obtain a protective effect against fungal pathogens.


3.Progress Report
This is the final report for project 6435-41000-097-00D terminated in September 2009. A bridging project (number 6435-41000-101-00D) covered FY-2010 research.

Research concerned the extraction and purification of plant antifungals. A patent was received in 2001, on CAY-1, a cayenne fungicidal compound known as a saponin, and we have continued its study where we purified two novel cayenne saponins, 1081 and 919, which are structurally very similar to CAY-1. Neither was antifungal; however, a mixture of these saponins (CAY-1, 1081, 919) in the ratio present in cayenne pepper is more antifungal than CAY-1 alone (data used to file a U.S. patent application).

Agricultural Research Service (ARS) collaborators (Winter Haven, FL) found CAY-1 active in lab studies against rot fungi in post harvest citrus. ARS collaborators (Poplarville, MS) found CAY-1 reduced plant pathogenic fungal growth in lab tests and prevented anthracnose lesions leaf tissue. However, semi-pure CAY-1 did not control foliar or fruit rot of strawberries in field trials.

Colleagues (National Institute of Health (NIH), Bethesda, MD) found CAY-1 acted synergistically in separate studies with Amphotericin B, Itraconazole (antifungal drugs), and dissolved silver against fungal pathogens, including two skin pathogens. Additional studies are needed to determine whether CAY-1 can possibly be used as a topical antifungal.

Bay leaf, okra, cotton seedlings, and barley were studied for their antifungal properties. The semi-purified extracts had antifungal properties, but the antifungal compounds were not purified.

The antifungal properties of commercial plant compounds were studied. Trans-2-hexenal and trans-2-heptenal (both from soybeans) were significantly lethal at low concentrations against Aspergillus and Fusarium species. Pumped, volatilized trans-2-hexenal killed Aspergillus flavus inoculated onto wet corn and prevented aflatoxin (a potent fungally produced carcinogen) production by this fungus. Bisabolol (plant oils) and dragosantol (synthetic bisabolol) are highly bactericidal and fungicidal against the fungal Aspergillus and Fusarium. Pinene and limonene, potent fungicides, may be useful as vapors or in an edible coating, to protect fruits and vegetables from fungal storage rot.

Volatiles produced by aflatoxin- and non-aflatoxin producing strains of Aspergillus flavus grown on corn were identified. Volatiles unique for the aflatoxin-producing strains used by Sensor Development Corporation to develop a prototype sensor, which will undergo Beta testing by the company in grain silos.

Studies into the microbicidal properties of visible light were initiated. Blue light (470nm) killed the harmful bacteria Leuconostoc mesenteroides, Pseudomonas, Staphylococcus, and Bacillus species. Exploratory experiments showed for the first time that a photosensitizing dye (Rose Bengal) in combination with visible blue light killed the fungus Aspergillus flavus conidia (spores or seeds).


4.Accomplishments
1. Potential of CAY-1 as an Antifungal Treatment of Post-Harvest Citrus. Post harvest citrus is susceptible to fungal rot particularly by Penicillium italicum and P. digitatum. Agricultural Research Service (ARS) researchers discovered and patented a novel fungicidal compound, CAY-1, from cayenne pepper in 2001. Under a Materials and Transfer Agreement with Brogdex, S.A. (Spain) during 2004, this company undertook a series of tests to determine whether CAY-1 could protect post-harvest citrus from infection by these fungi. Results showed that CAY-1 was superior to Imazalil sulfate, the standard fungicidal treatment for stored citrus. This work was later confirmed by ARS scientists located in Winter Haven, Florida. Results suggest that CAY-1 would be an excellent, natural fungicidal treatment for stored citrus.

2. Identification of Volatile Compounds Produced by Aspergillus flavus on Corn. Aspergillus flavus is naturally present on corn. Under the right conditions this fungus will grow on the corn and produce aflatoxin B1, the most potent hepatocarcinogen known. The fungal growth and subsequent aflatoxin contamination of the corn renders it unusable for food and feed. All fungi produce small amounts of volatile compounds when growing. Agricultural Research Service scientists in New Orleans, LA, have identified volatile compounds that are unique for the toxigenic strains of this fungus. Sensor Development Corporation is using this data to develop a real-time sensor of Aspergillus flavus growing on stored corn. This project will provide a sensor that will alert grain companies to the presence of Aspergillus flavus growth and allow them to quickly remove the contaminated corn before the fungal growth and aflatoxin can spread to healthy corn kernels.


Review Publications
Abril, M., Curry, K.J., Smith, B.J., De Lucca Ii, A.J., Boue, S.M., Wedge, D.E. 2009. Greenhouse and Field Evaluation of the Natural Saponin CAY-1, for Control of Several Strawberry Diseases. International Journal of Fruit Science. 9:3,211-220.

Last Modified: 7/31/2014
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