Location: Natural Products Utilization Research
2005 Annual Report
Since the early 1970s, both the medical and agricultural communities have struggled with the evolution of pathogen resistance to antimicrobial agents. Effective control of resistant pathogens has required increased necessity for repeated chemical applications and aggressive disease resistance management strategies. Increasing incidence of chemical resistance in fungal plant pathogens and loss of available fungicides for disease control in minor crops are two factors that drive the need for new fungicides.
Our approach to solving disease control, resistance issues, and the decreasing availability of agrochemicals in the market place is to identify naturally occurring chemicals from plants, pathogens, and marine and terrestrial organisms. Natural products often have new chemical structures that have not been realized or synthesized by organic chemists. Particularly desirable is the discovery of novel prototype antimicrobial agents representing new chemical classes that operate by different modes of action than existing antifungal agents and, consequently, lack cross-resistance to chemicals currently used. Following natural product leads offers an efficient approach to discovering and optimizing new agrochemicals for disease control. How serious is the problem? Why does it matter?
Increasing incidence of resistance to fungicides by plant pathogens and loss of existing chemistry for disease control are two factors that drive the need to search for new agricultural fungicides. In addition, the desire for safer agrochemicals with less environmental and mammalian toxicity is a major concern. Particularly desirable is the discovery of novel prototype antimicrobial agents representing new chemical classes that lack cross-resistance to chemicals currently used. Following natural product leads offers an efficient approach to discovering and optimizing new agrochemicals for disease control. Due to the continuing development of microbial resistance in agriculture, discovery of new antimicrobial substances is an important, if not urgent, research objective. Natural product derived disease control agents and those compounds considered Generally Regarded as Safe (GRAS) should essentially reduce registration costs, and therefore, provide for many more crops as potential benefactors and allow for the advancement of more potential candidate chemicals. Therefore, many minor crops are potential benefactors of natural product-based fungicides. Implementation of disease control measures that utilize low application rates of effective chemicals is imperative to maintaining cost-effective disease controls and farm profitability.
How does it relate to the National Program(s) and National Program Component(s) to which it has been assigned?
The discovery and development of new natural product fungicides fulfills both major components of the NPS 306 mission for US agriculture. Quality Characterization, Preservation, and Enhancement (Component.
Year 1 - Identify active compounds for evaluation (a continuing process). - Internal NPURU submitted samples. - Internal University of Mississippi submitted samples. - External USDA ARS samples. - External non-USDA samples.
Year 2 - Each active pure compound is studied progressively. - Actives are evaluated in 96-well plate system -> IC50, IC95 or MIC. - Invention disclosures filed. - Re-isolation of actives initiated.
Year 3 - Detached leaf and greenhouse studies initiated. - Patent application is prepared if appropriate. - Microscopic studies initiated. - Re-isolation of actives initiated.
Year 4 - Active compounds is either moved on or eliminated. - Detached leaf and greenhouse studies repeated. - Compound scale up, recollection, or fermentation initiated. - Microscopic studies repeated. - Mode of action studies initiated.
Year 5 - Compound scale up, recollection, or fermentation initiated. - Mode of action studies are repeated. - Greenhouse studies repeated. - Experimental field plots initiated.
Relative to Project Number 6408-22430-003-01M, a Memorandum of Understanding between ARS and Chiang Mai University, Chiang Mai, Thailand, the project report is as follows: the project was not funded in 2004-2005 and future milestones, goals and objectives will be initiated if funding is obtained.
Relative to Project Number 6408-22430-003-02S, a Specific Cooperative Agreement between ARS and The University of Southern Mississippi, the progress report is as follows: promising results from our greenhouse studies suggest continuing to field studies for these two natural product-based fungicides since ultimately screening under field conditions constitutes the final stage in a natural product discovery program before going into commercial development and production. The principal advantage of using new fungicides primarily isolated from natural sources over chemical synthesis or modification of existing agents is that natural products represent a vast untapped reservoir of chemical compounds. In addition, the probability of discovering new fungicides with different modes of action and different chemical structures and, therefore, dissimilar toxicities and cross-resistance is extremely beneficial for widening the options we have in pest control.
Over the life of the research project, several in vitro and detached leaf assays and novel microscopic techniques were developed to evaluate natural product compounds that are often available only in very low concentrations. Bioautographic and 96-well antifungal assays have identified numerous natural product compounds as effective antifungal agents against several fungal plant pathogens of strawberry and other small fruits. These assays were also capable of evaluating chemical resistance and sensitivity profiling of Botrytis cinerea, Colletotrichum spp. and Fusarium species. Through collaborations with the Small Fruit Research Station (SFRS), Poplarville, MS, a new detached leaf assay was developed to study the efficacy of natural fungicides directly on the leaf surface, establish effective concentrations for disease control, and evaluate the ability of a compound to move systemically with in the leaf. New microscopic techniques that can evaluate spore viability directly on the leaf surface were developed with University of Southern Mississippi collaborators. Evaluation of new fungicides with low mammalian and environmental toxicity to control Botrytis fruit rot and flower blight, Fusarium wilt, and anthracnose use will help assure the safety of our food supply and the sustainability of small fruit industry.
An in-depth project studying the antifungal chemistry of mushrooms has yielded several potential sources of new antifungal agents. Development of a new Optimum Performance Laminar Chromatography (OPLC) high throughput platform for fungicide discovery will progress in 2004.
Further interaction with scientists and publications will promote the use and successful adaptation of these assay techniques and new fungicide technologies in agriculture. Sampangine mode of action is being evaluated this year through a 2 year Non-funded Cooperative Agreement with Paradigm Genetics, Inc. Technology transfer should increase during the next five years as more scientists use and report on natural product discovery and evaluation techniques. Technology constraints primarily include the increasing cost of discovering and developing new fungicides. Technology transfer in the form of CRADAs with agrochemical industry partners covering USDA-discovered fungicides is progressing slowly. Once there are successful compounds in the marketplace, durability of the technology should be long term and we expect that impact will be high.
Wedge’s research with Dale Nagle resulted in a new patent -- US No. 6,844,353 -- sampangine-based compounds can control fungi that cause gray mold, anthracnose, and vascular wilt was used as a lead story in ARS Information and News Service http://www.ars.usda.gov/News/docs.htm?docid=1261 ‘Medicinal Compound Gets New Life as Fungicide’ (February 23, 2005).