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United States Department of Agriculture

Agricultural Research Service

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2012 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:
This is the final report for project 1275-22000-250-00D. Over the five years of this project substantial progress was made. Italian ryegrass (IR) was tested as a cover crop for reducing pathogen and pest populations in soybean fields. There was no impact on numbers of insect pests, plant-parasitic nematodes, or beneficial soil mites and nematodes. The study indicated that use of IR for improving soybean yields is dependent on a number of complex factors that growers must assess. Winter rye is a commonly used cover crop, and our lab and greenhouse studies showed that rye natural products were toxic to nematodes; we also determined host status of cultivars to root-knot nematodes (RKN). In GA field studies, most rye cultivars in strip tillage suppressed the weed Palmer amaranth in peanut and cotton fields compared to winter fallow. This research assists growers in improving use of rye cover crops as nematode and weed management agents. RKN in peach orchards can cause decreased yields, and tall fescue was investigated as a preplant ground cover for suppressing RKN populations. Tall fescue was a poor host or nonhost for some RKN species, and nematicidal natural compounds were produced by a tested cultivar. This work provides peach growers with an approach that has potential for reducing reliance on chemical pesticides for suppressing RKN populations. In studies with amendments, chicken manure compost reduced RKN numbers on cocoa seedlings in greenhouse studies and improved plant growth. Successful application of compost can provide subsistence growers with affordable nematode management strategies. Mustard seed meals were tested to determine phytotoxicity to vegetable crops and efficacy against RKN. The research determined the length of time needed from amendment to transplant of cash crops, and demonstrated that a combination of seed meals was effective against RKN. Experiments were completed on an alkaline-stabilized biosolid to suppress RKN, and results from multi-state projects demonstrated that this amendment must be applied in a site-specific manner to achieve plant-parasitic nematode control. In studies on the beneficial bacterium Pseudomonas fluorescens, tested isolates did not affect RKN population numbers on watermelon. Selected nematode species were exposed to an antibiotic produced by these bacteria, and the antibiotic was toxic to some species but not others. This research aids in determining whether the antibiotic is active against target and nontarget nematode species. In research on natural products for nematode management, the essential oil from cloves (active against multiple target organisms) was tested for effects on RKN. With the tested formulation, RKN populations were not consistently reduced with concentrations that were not phytotoxic to some of the tested vegetable crops. Research collaborations on other plant-derived products as natural nematicides led to an invention disclosure. The overall impact of the research in the five years of this project is to improve use of management strategies for nematodes, promote sustainable agricultural practices, and provide growers with alternatives to conventional nematicides.

4. Accomplishments
1. Mustard seed meal combinations suppress nematode populations on vegetable crops. Mustard seed meal is a byproduct formed when oil is extracted from seeds during production of biodiesel, and the seed meal is applied as an amendment to agricultural soils to act as a fertilizer and to suppress populations of weeds and of soilborne pests and pathogens. Because seed meal chemistry varies depending on the plant species from which it was produced, seed meal combinations have potential to provide a range of activities against pests and pathogens. In collaboration with an ARS scientist from Corvallis and researchers from the Universities of Idaho and Maryland, we applied seed meals individually and in combinations to determine phytotoxicity to tomato plants and suppressive effects on root-knot nematode populations attacking tomato roots. Tomato shoots were longest when seedlings were transplanted at least 2 weeks after the mustard seed meal treatments were added to soil. Because the formation of nematode-containing root galls was decreased in some treatments, the results are significant, indicating the potential utility of mustard seed meal combinations for nematode management in tomato cropping systems. Therefore, crop advisers will be able to provide improved recommendations for the use of seed meals in controlling nematodes and other pests.

Review Publications
Ibrahim, H., Alkharouf, N., Meyer, S.L., Sanad, M., El-Din, A., Hussein, E., Matthews, B.F. 2010. Post-transcriptional gene silencing of root knot-nematode in transformed soybean roots. Experimental Parasitology. 127:90-99.

Meyer, S.L., Zasada, I.A., Orisajo, S.B., Morra, M.J. 2011. Mustard seed meal mixtures: management of Meloidogyne incognita on pepper and potential phytotoxicity. Journal of Nematology. 43(1):7-15.

Last Modified: 2/23/2016
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