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United States Department of Agriculture

Agricultural Research Service

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2008 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 populations 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
Activity of Bacterial Products against Plant Pathogens Some species of the bacterium Pseudomonas are active against soilborne plant-pathogenic fungi and bacteria, and commercial products are available for use in suppressing plant diseases. Much of the activity of these beneficial bacteria is due to production of antibiotics, and pseudomonads that produce the antibiotic 2,4-diacetylphloroglucinol (DAPG) are one group that have been extensively investigated. DAPG-producing pseudomonads were therefore selected for ability to suppress pathogens on watermelon, specifically root-knot nematode and Fusarium oxysporum f. sp. niveum (the fungus that causes Fusarium wilt). Greenhouse studies indicated activity of certain isolates against these plant pathogens, and selected isolates are being further investigated in the greenhouse and field. Fescue as a Nematode Antagonist Root-knot nematodes are also among the most economically important plant-parasitic nematodes that attack peach trees. As an alternative to conventional chemical controls, preplant use of a fescue groundcover is being investigated in Georgia for suppression of nematode populations. The study in Georgia has indicated that fescue is a nonhost for certain root-knot nematode species, but may allow limited reproduction of other species. Populations of an untested species of root-knot nematode are being grown in Maryland to determine fescue susceptibility and toxicity of root extracts. Activity of Fungus Exudates against Nematodes Ramicandelaber is a recently described fungal genus, and Nematology Laboratory (NL) members isolated the species R. longisporus from soybean cyst nematodes in China. This species has been reported only three times throughout the world, and has therefore been little studied. The NL isolate produced nematotoxic natural products in culture, and was further investigated for activity against nematodes. Fractionation of the culture filtrate indicated that the active compound might be volatile in nature. All of these studies directly support National Program 303, Action Plan Component IV: Biological and Cultural Strategies for Sustainable Disease Management, specifically Problem Statements 4A: Biological and Cultural Control Technologies; 4B: Pathogen, Plant and Antagonist Interactions; and 4C: Application of Sustainable Disease Management Tools.

4. Accomplishments
1. Effects of Natural Compounds from Rye Cover Crops against Root-Knot Nematodes. Rye is one of the grasses that produce a chemical called DIBOA, which can be toxic to nematodes and other organisms that attack these plants. DIBOA was therefore applied to soil in investigations to determine its longevity and ability to suppress populations of plant-parasitic nematodes on a host crop; cucumber was selected as the host. The study demonstrated that DIBOA breaks down quickly in the soil, and that high concentrations of DIBOA in the soil are necessary to reduce root-knot nematode numbers. At low concentrations, this compound may not be a major factor in ability of rye cover crops to suppress root-knot nematode populations. This research will assist growers in determining whether DIBOA production should be considered as an important factor when selecting rye cultivars to be used as cover crops in nematode-infested fields. This research supports National Program 303, Action Plan Component IV: Biological and Cultural Strategies for Sustainable Disease Management, specifically Problem Statements 4A: Biological and Cultural Control Technologies; 4B: Pathogen, Plant and Antagonist Interactions; and 4C: Application of Sustainable Disease Management Tools.

5. Significant Activities that Support Special Target Populations

Review Publications
Meyer, S.L., Lakshman, D.K., Zasada, I.A., Vinyard, B.T., Chitwood, D.J. 2008. Dose-response effects of clove oil from Syzygium aromaticum on the root-knot nematode Meloidogyne incognita. Pest Management Science. 64:223-229.

Lee, J.H., Choi, S.H., Kwon, O.S., Shin, T.J., Lee, J.H., Lee, B.H., Yoon, I.S., Pyo, M.K., Rhim, H., Lim, Y.H., Shim, Y.H., Ahn, J.Y., Kim, H.C., Chitwood, D.J., Lee, S.M., Nah, S.Y. 2007. Effects of ginsenosides, the active ingredients of Panax ginseng, on development, growth, and life span of Caenorhabditis elegans. Biological and Pharmaceutical Bulletin. 30(11):2126-2134.

Last Modified: 2/23/2016
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