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United States Department of Agriculture

Agricultural Research Service

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2010 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
We collaborated with a scientist from South China Agricultural University on testing plant-derived products as natural nematicides. In the laboratory and greenhouse, some compounds were active against nematodes, and an invention disclosure was filed based on this research. Cover crops can provide growers with means to minimize diseases, pests and weeds, and to reduce erosion and provide nitrogen. In collaboration with researchers from the University of Maryland and the University of Hawaii, soil samples were taken from three Maryland fields: 1) summer squash with a Sunn hemp cover crop; 2) soybean with an Italian rye cover crop; and 3) corn with rye, crimson clover, and rye/clover mix as cover crops. Beneficial and plant-parasitic nematode communities were analyzed to determine effects of these cover crops; the results will assist growers with selecting cover crops that best reduce nematode populations in the soil. In collaboration with ARS scientists in Georgia and Beltsville, samples from a winter rye cover crop were analyzed for chemical compounds called benzoxazinoids which are produced by rye plants and are toxic to plant-parasitic nematodes. The project will assist peanut and cotton growers in selecting rye cultivars. Root-knot nematodes attack peach trees and can cause economic losses. In collaboration with an ARS researcher in Georgia, we investigated fescue for production of extracts and root exudates that are toxic to these nematodes, to determine mechanisms that make fescue a poor host. This will assist in using fescue as a groundcover rotation crop, providing an alternative to chemical nematicides for suppressing nematode populations on peach trees. We collaborated with a scientist from the Cocoa Research Institute of Nigeria and with Beltsville ARS colleagues in testing chicken manure compost as an amendment for suppressing nematode populations on cocoa seedlings. Nigeria is one of the top five cocoa bean producing countries in the world, and successful application of amendments will provide growers with affordable nematode management strategies. Seed meals produced from plants in the mustard family during production of biodiesel fuel can be useful for pest management. In collaboration with a scientist from ARS at Corvallis, we tested mustard meals toxic to plant-parasitic nematodes for phytotoxicity to crop plants, to determine optimal rates of application. We conducted studies in collaboration with other researchers from ARS in Beltsville, the University of Maryland, and Benha University (Egypt) on natural products and plastic tarp as alternatives to conventional nematicides for suppressing populations of nematodes and human pathogens on vegetable and leafy green crops in hoophouses. These results will aid in providing options for pathogen management.

4. Accomplishments
1. Avoiding phytotoxicity of mustard seed meals to crop plants. Mustard seed meal is produced when oil is extracted from seeds from plants in the mustard family. These seed meals contain naturally occurring chemicals that make them of interest as management agents for weeds and soilborne pathogens. Previous studies indicated that seed meals from two species of mustard, Brassica juncea and Sinapis alba, are nematotoxic. However, because of the potential for phytotoxicity of these meals, it is advantageous to know the amount of time required between mustard seed meal application and planting to avoid phytotoxicity. Consequently, scientists at Beltsville, in collaboration with an ARS scientist from Corvallis, tested the meals alone and in combinations to determine toxicity to pepper seedlings and to germinating lettuce seeds. Treatment with seed meal from B. juncea tended to be the least toxic overall to pepper seedlings, indicating that nematotoxic rates of B. juncea could be applied relatively close to the time of pepper transplant. Germinating lettuce seeds did not clearly demonstrate the same greater sensitivity to S. alba meal. This research is valuable to scientists optimizing the use of seed meal amendments for managing plant-parasitic nematodes without toxicity to crop plants, with growers eventually benefitting.

Last Modified: 2/23/2016
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