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United States Department of Agriculture

Agricultural Research Service

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2011 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
Cover crops and green manures can increase crop yields, enhance nutrient absorption and soil quality, and decrease fertilizer and pesticide use and soil erosion. In collaboration with researchers from the University of Maryland and the University of Hawaii, we tested vegetable crop fields in Maryland for effects of cover crops/green manures on communities of nematodes and of nematode-trapping fungi (beneficial microbes that parasitize nematodes). Cover crops included crimson clover and either rye or barley (dependent on the field). These studies will determine whether the cover cropping/green manure systems are efficacious for increasing populations of beneficial microbes and improving soil health and crop yields. Isolates of the bacterium Pseudomonas fluorescens can be applied to fields as beneficial microbes for suppressing plant diseases. In collaboration with scientists from the University of Maryland/University of Delaware and the Ohio State University we tested a P. fluorescens isolate for suppression of soilborne plant diseases on a vegetable crop. Under the experimental conditions, the tested isolates did not suppress the target pathogens. The research will be useful for scientists and companies interested in biocontrol agents for these pathogens. Root-knot nematodes are a major economic problem on young peach trees, and can cause decreased yields if appropriate management practices are not followed. In collaboration with an ARS scientist in Georgia, we are investigating the use of fescue for management of these plant-parasitic nematodes. We assayed fescue roots and shoots for production of compounds toxic to one root-knot nematode species. This was done to ascertain if plant-derived compounds contribute to poor host status of fescue to this nematode, and if the compounds can be used as natural products for suppressing nematode populations. Because extracts demonstrated some nematotoxicity, this work will contribute to the use of fescue as a preplant ground cover alternative to synthetic chemical pesticides for suppressing nematode populations in peach orchards. Chia is planted as a food crop and is being investigated as a cover crop for suppressing weeds. ARS scientists in Beltsville investigated the host status of chia to root-knot nematode to determine whether this nematode would be suppressed in soils where the plant is grown. Chia was a host for the nematode.

4. Accomplishments
1. Mustard seed meal amendments for suppression of root-knot nematodes. Mustard seed meal is a waste byproduct of the biodiesel industry, resulting from the extraction of oil from seeds. Methods are being developed to utilize these seed meals in agricultural applications, thereby eliminating waste disposal issues and augmenting profits while enhancing agricultural practices. Mustard seed meals are suppressive to pests and pathogens and are consequently used as soil amendments for management of soilborne pathogens and weeds. The chemistry of seed meals differs among various plant species, so there is potential for a seed meal combination to provide a wider range of activities against pathogens and pests than an individual seed meal application. ARS scientists at Beltsville, in collaboration with an ARS scientist from Corvallis, and researchers from the University of Idaho and the Cocoa Research Institute of Nigeria, tested two seed meals alone and in combinations for suppression of root-knot nematodes on pepper plants. The seed meals were from two species in the mustard plant family, and differ from each other in types of chemicals that are toxic to plants. In addition, one seed meal has demonstrated greater toxicity to nematodes than the other seed meal. Longer pepper shoots, greater plant weights, and lower galling indices resulted from two of the seed meal treatments. These two treatments and others containing the seed meal that is more toxic to nematodes also produced the lowest numbers of nematode eggs per root weight. This demonstrated that a combination could be as effective against nematodes as an individual seed meal, potentially allowing for greater weed suppression along with reductions in nematode populations. The impact is that crop advisors are now able to provide better recommendations for the use of mustard seed meals as pest and weed control agents.

Review Publications
Nyczepir, A.P., Meyer, S.L. 2010. Host status of endophyte-infected and noninfected tall fescue grass to Meloidogyne spp. Journal of Nematology. 42(2):151-158.

Roberts, D.P., Maul, J.E., Mckenna, L.F., Emche, S.E., Meyer, S.L., Collins, R.T., Bowers, J.H. 2010. Selection of genetically diverse trichoderma spp. isolates for suppression of phytophthora capsici on bell pepper. Canadian Journal of Microbiology. 56:864-873.

Meyer, S.L., Halbrendt, J.M., Carta, L.K., Skantar, A.M., Liu, T., Abdelnabby, H.M., Vinyard, B.T. 2010. Toxicity of 2,4-diacetylphloroglucinol (DAPG) to plant-parasitic and bacterial-feeding Nematodes. Journal of Nematology. 41(4):274-280.

Timper, P., Davis, R.F., Webster, T.M., Brenneman, T., Meyer, S.L., Zasada, I.A., Cai, G., Rice, C. 2011. Response of root-knot nematodes and Palmer amaranth to tillage and rye green manure. Agronomy Journal. 103(3):813-821.

Last Modified: 2/23/2016
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