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United States Department of Agriculture

Agricultural Research Service

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2009 Annual Report

1a. Objectives (from AD-416)
Objective 1: Enhance the effectiveness of soil amendments and microbes as management agents for plant-parastic nematodes. Sub-objective 1.A) Improve the efficacy and spectrum of activity of nitrogenous soil amendments and beneficial microbes as plant-parasitic nematode management agents. Sub-objective 1.B) Evaluate ecological interactions among plants, soils, microorganisms and effective management agents to understand and create environments unfavorable to plant-parasitic nematodes. Objective 2: Expand utilization of cover crops as nematode management tools by characterizing nematode-suppressive phytochemicals, and develop plant- and microbe-based nematotoxic products for nematode management. Sub-objective 2.A) Determine the mode of action of rye and other cover crops that produce natural plant compounds suppressive to plant-parasitic nematodes, and develop or improve nematode management systems by maximizing the activity of these compounds. Sub-objective 2.B) Isolate nematotoxic products from plants and microbes and evaluate the products as natural chemical management agents for plant-parasitic nematodes.

1b. Approach (from AD-416)
1A) Greenhouse and field trials will be conducted to improve the usefulness of nitrogenous amendments, such as biosolids, for managing plant-parasitic nematodes. Beneficial microbes, particularly species of Trichoderma and Pseudomonas, will be investigated for activity against nematodes and tested in the greenhouse and field for suppression of nematode populations. 1B) Studies will be conducted at the Farming Systems Project (FSP), Beltsville, MD, in different cropping systems to identify management practices which promote plant-parasitic nematode regulation and lead to development of suppressive soils. Soil nematodes with undetermined feeding habits will be studied to determine primary food sources in their native habitats. 2A) A diverse set of rye cultivars will be evaluated for M. incognita host status and benzoxazinoid content, cultivars will be tested in field trials for effects on nematode populatons on cotton and peanut, and fate of benzoxazinoids in soil will be determined. 2B) To identify nematotoxic activity from plant- and fungal-derived compounds, laboratory assays with root-knot nematodes will be conducted with various compounds, such as clove oil, fungal culture broth, and fescue root extracts. Promising compounds will be further tested in the greenhouse.

3. Progress Report
Mechanism of toxicity of bacteria to nematodes. Certain isolates of Pseudomonas fluorescens, a soil-dwelling bacterium, can suppress plant diseases caused by fungi and bacteria. These bacteria may have more than one mode of action, including induced resistance in host plants, and production of toxins and antibiotics. In collaboration with researchers from Ohio State University and the University of Maryland, the Beltsville Nematology Laboratory tested several isolates of P. fluorescens in the greenhouse and in microplots for activity against root-knot nematode and a wilt-causing fungus on a vegetable crop. In a related but separate project, selected nematodes were also exposed to one of the antibiotics produced by the bacteria to determine the effects of this antibiotic on the nematodes. This research aids in determining usefulness of the antibiotic-producing bacteria for managing these plant pathogens. Winter rye cover crop. Winter rye (Secale cereale) utilized as a cover crop has many beneficial attributes. Rye grows quickly, provides abundant above ground biomass, produces a good root system to minimize erosion, captures residual nitrogen that is later released for the subsequent crop, and suppresses weeds and insect pests. Rye exhibits antagonism to other organisms, including plants, fungi, bacteria, insects and nematodes. Some of the antagonism is due to natural products that rye produces. ARS collaborators in Georgia planted rye as a cover crop to study effects on populations of plant-parasitic nematodes, with biomass samples provided to Beltsville collaborators for chemical analysis. The project will assist growers in selection of rye cultivars. Fescue groundcover. Root-knot nematodes are an economically important pathogen on peach trees. An ARS collaborator in Georgia is testing preplant use of fescue as an alternative to synthetic chemicals for suppressing populations of plant-parasitic nematodes. A Beltsville Nematology Laboratory collaborator is testing the ability of a root-knot nematode species to infect the fescue, and is examining the survival of the nematode when fescue is grown in soil. Demonstration of nematode suppression by fescue would provide growers with new management strategies. Mustard meals for nematode management. Oilseeds are used for production of biodiesel fuel, and seed meals produced from plants in the mustard family can be useful for pest management and as fertilizers. In a collaborative research project with ARS in Oregon and with the University of Idaho, mustard meals from four species in the mustard family were tested for toxicity to plant-parasitic nematodes. At the Beltsville Nematology Laboratory, the meals were tested against a species of root-knot nematode, which is the most economically important nematode on crop plants worldwide.

4. Accomplishments
1. Toxicity of the natural antibiotic 2,4-diacetylphloroglucinol (DAPG) to nematodes. Some beneficial isolates of the bacterium Pseudomonas fluorescens produce DAPG, which is active against numerous organisms, including plants, fungi, viruses, and bacteria. Application of DAPG-producing pseudomonads can result in increased crop yields. To determine if production of this compound by bacteria in the plant rhizosphere would have potential to suppress nematode populations in the soil, scientists at the Beltsville Nematology Laboratory, in cooperation with scientists from the Pennsylvania State University in Biglerville, tested DAPG for activity against seven different nematodes and developed models for effects of DAPG at varying concentrations. The tests included plant-parasitic and bacterial-feeding species, to ascertain if target nematodes and nontarget nematodes would be affected. Effects of DAPG were variable, depending on the nematode species and life stage being studied, and ranged from toxic to stimulatory. This research has allowed scientists to determine which species of plant-parasitic nematodes would be optimal targets for application of DAPG-producing biocontrol bacteria.

Review Publications
Meyer, S.L., Rice, C., Zasada, I.A. 2009. DIBOA: Fate in Soil and Effects on Root-knot Nematode Egg Numbers. Soil Biology and Biochemistry. 41:1555-1560.

Meyer, S.L.F., Lakshman, D.K., Zasada, I.A., Vinyard, B.T., Chitwood, D.J. 2008. Phytotoxicity of clove oil to vegetable crop seedlings and nematotoxicity to Root-knot Nematodes. HortTechnology. 18:631-638.

Meyer, S.L., Chitwood, D.J. 2008. Edna Marie Buhrer (1898-1988) and Grace Whitney Sherman Cobb (1905-1993): Pioneering nematologists at the USDA Nematology Laboratory. In: Ristaino, J.B., editor. Pioneering Women in Plant Pathology. St. Paul, MN: American Phytopathological Society Press. p. 67-83.

Last Modified: 2/23/2016
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