2013 Annual Report
1a.Objectives (from AD-416):
1. Identify and inhibit the functions of nematode-specific molecules (proteins and lipids) critical to fundamental life processes in plant-parasitic nematodes.
2. Improve the effectiveness of nematode management based upon nematode-antagonistic cover crops and soil amendments.
3. Identify chemical components of nematode-suppressive cover crops and other plant-derived products responsible for activity against nematodes.
1b.Approach (from AD-416):
1. Determining the roles and modes of action of peptides and associated proteases and lipids and steroids that regulate plant-parasitic nematode development and hatching will identify internal targets for inhibition. Responses of these molecular targets to external signals, such as plant chemicals, will identify pathways to exploit to disrupt normal life processes.
2. Evaluating mixed species cover crops and green manures and application of improved mustard seed meal amendment combinations will lead to enhanced suppression of plant-parasitic nematodes and increased crop yields relative to single species strategies. Planting grafted vegetables in mustard seed meals and use of beneficial microbes will suppress soilborne diseases on vegetable crops and increase yields.
3. Determining how nematodes respond physiologically to plant- and microbe-derived natural products will identify compounds that can be used for nematode management, provide efficient and rapid screens for discovering nematode control compounds, and enhance the identification, selection and use of organisms for suppressing nematode populations.
Per Objective 1, the normal development and reproduction of plant-parasitic nematodes are essential for these organisms to infect plants and damage crops. Consequently, understanding what molecules within nematodes might make good targets for disruption of normal metabolism will provide powerful information for the design of new control strategies. Working with the soybean cyst nematode and the root-knot nematode, the two most economically destructive nematodes in the United States, we discovered that plant chemicals called catechins affect hatching and metabolism of these parasites. Various catechins were more potent than others in suppressing hatch, and that there were differences in response between the two species. Catechins were found to inhibit specific nematode enzymes, also with analog and species differences. In addition, we discovered that the soybean cyst nematode itself might provide a source for potent and specific nematode enzyme inhibitors. Such information is essential to guiding future experiments to disrupt the action of molecules fundamental to nematode processes.
The use of cover crops and green manure amendments has many potential benefits, including enhanced soil quality, nutrient absorption and crop yields, and decreased soil erosion, fertilizer use and pesticide application. In pursuit of Objective 2, in collaboration with researchers from the University of Maryland and the University of Hawaii, we evaluated soil with incorporated cover crops/living mulches (barley and crimson clover) and associated soil microbial communities in the greenhouse and field for effects on nematode communities on vegetable crops (including zucchini, green bean and broccoli). In collaboration with an ARS scientist from Corvallis and researchers from the Universities of Idaho and Maryland, mustard seed meal was tested in the greenhouse and field for phytotoxicity to tomato and for suppression of root-knot nematode populations. These studies will determine whether selected cover crops and soil amendments are effective for improving soil health, decreasing populations of plant-parasitic nematodes, and increasing crop yields.
Root-knot nematodes cause major economic problems on crop plants worldwide; several plant species are known to suppress root-knot nematode populations in soil. In collaboration with ARS scientists in Georgia and Beltsville, tall fescue is being investigated in Objective 3 for management of plant-parasitic nematodes. Extracts and exudates from tall fescue roots and shoots on root-knot nematodes were discovered to have toxic effects on nematodes, thereby indicating that compounds in these extracts could contribute to the poor host status of tall fescue to root-knot nematodes. These studies will contribute to optimizing use of tall fescue as a preplant ground cover in peach orchards as an alternative to application of chemical pesticides for suppressing nematode populations.
Natural plant molecules disrupt nematode development. Safe strategies for managing plant-parasitic nematodes should effectively control these target pests while having minimal impact upon the environment and non-target species. Using the most economically important plant nematodes in the United States, the soybean cyst nematode and the root-knot nematode, we found that plant chemicals called catechins inhibit nematode hatching and also significantly inhibit nematode enzymes called proteases. Various catechins were more potent than others in suppressing hatch, and that there were differences in response between the two species. The catechins affect three specific proteases that are part of a complex structure central to the health of the cell and nematode survival. Without proper protease function, nematodes fail to develop and will die. This discovery is important because not only it is the first to demonstrate a molecular basis for how this category of plant chemical can suppress plant-parasitic nematode development and reproduction at low doses, it also indicates that catechins might be used directly as nematode control agents. This information is of great value to scientists developing precision treatment strategies for controlling plant-parasitic nematodes and to growers seeking to decrease synthetic chemical use in crop protection.
Meyer, S.L.F., Nyczepir, A.P., Rupprecht, S.M., Mitchell, A.D., Martin, P.A., Brush, C.W., Chitwood, D.J., Vinyard, B.T. 2013. Tall fescue ‘Jesup (Max-Q)’: Meloidogyne incognita development in roots and nematotoxicity. Agronomy Journal. 105(3):755-763.
Hooks, C.R., Wang, K., Meyer, S.L., Lekveishvili, M., Hinds, J., Zobel, E., Rosario-Lebron, A., Lee-Bullock, M. 2011. Impact of no-till cover cropping of Italian ryegrass on above and below ground faunal communities inhabiting a soybean field with special emphasis on soybean cyst nematodes. Journal of Nematology. 43(3-4):172-181.
Meyer, S.L.F., Orisajo, S.B., Chitwood, D.J., Vinyard, B.T., Millner, P.D. 2011. Poultry litter compost for suppression of root-knot nematode on cacao plants. International Journal of Nematology. 21(2):153-162.
Masler, E.P. 2013. Effects of catechin polyphenols and preparations from the plant-parasitic nematode Heterodera glycines on protease activity and behavior in three nematode species. Journal of Helminthology. DOI: 10.1017/S0022149X13000254.
Masler, E.P. 2013. A comparison of the FMRFamide-like peptide proteolytic activities of preparations from two plant-parasitic nematodes (Heterodera glycines and Meloidogyne incognita): possible targets for novel control. Journal of Helminthology. 87(1):71-77.
Masler, E.P. 2013. Free-living nematode peptides. In: Kastin, A., editor. Handbook of Biologically Active Peptides. 2nd edition. New York, NY: Elsevier/Academic Press. p. 247-254.