Location: Mycology and Nematology Genetic Diversity and Biology Laboratory
2018 Annual Report
Objectives
Objective 1: Identify and characterize nematode proteins and lipids that inhibit the metabolic pathways critical to fundamental processes in plant-parasitic nematodes.
Sub-objective 1A: Discover and characterize endogenous nematode agonists or antagonists, including bioactive peptides, which affect metabolism and behavior.
Sub-objective 1B: Characterize protease and other enzyme profiles in plant-parasitic nematodes, and determine their roles and modes of action in regulating development and hatching.
Sub-objective 1C. Identify lipids and steroids with likely regulatory roles in plant-parasitic nematodes and design methods to disrupt this regulation.
Objective 2: Improve the effectiveness of nematode management based on amendments and beneficial organisms, and by identifying and characterizing plant, microbe or nematode products antagonistic to nematodes.
Sub-objective 2A: Evaluate cover crops, soil amendments and microbes for suppressing plant-parasitic nematode populations on agricultural crops.
Sub-objective 2B: Determine effects of natural products from plants, microbes, and nematodes on plant-parasitic nematodes, and evaluate selected nematode-antagonistic products as potential nematotoxins.
Approach
1. Discovering and characterizing internal plant parasitic nematode regulatory molecules, including peptides, proteases, inhibitors, and nematode-unique lipids and steroids, that act as effectors of behavior, development, hatching and metabolism, will provide novel targets for disruption of nematode life processes. Analyzing external signals, including plant chemicals, and their interactions with internal nematode pathways, will expand the number of molecular targets for nematode control.
2. Evaluating cover crops, soil amendments, microbes, and other beneficial agents, and improving strategies for their application, will lead to enhanced plant-parasitic nematode suppression and improved plant yields. Assessing the biological effects of selected beneficial organisms, and the analysis of natural products from plant, microbial and nematode origins, will reveal novel nematotoxins and other suppressive agents for plant-parasitic nematode control and agricultural crop protection.
Progress Report
Discovering and characterizing nematode molecular interactions are essential for the development of new, biologically informed control strategies. Female soybean cyst nematodes which, along with root-knot nematodes, represent the most economically destructive nematodes in the United States, were established as sources of potent and specific inhibitors of nematode enzymes called proteases. Proteases are essential for plant-parasitic nematode metabolism and reproduction, and are present in a number of functional families. All functional protease families are inhibited, but inhibitor potencies are greater in root-knot than in soybean cyst nematodes. The female cyst is also a rich source of proteases that can influence metabolism and embryonic development. We found that the activities of these proteases can be nearly eliminated by separating some components of cyst contents, and then restored by re-combining components. This indicates that cyst proteases require co-factors to function, and is the first such observation for any plant-parasitic nematode. This discovery provides a new avenue to explore for novel control agents. Cyst protease inhibitors, species specificity, and the indication of essential co-factors, have revealed fundamental properties of nematode molecular interactions. Such information is essential for exploiting natural products in generating novel and specific agents that disrupt internal molecular interactions for nematode control.
Amendments, beneficial organisms (including plants) and natural products are used by growers to suppress populations of plant-parasitic nematodes, supplement conventional fertilizers and pesticides, and improve soil health and crop yields. In research conducted with scientists from the Universities of Maryland and Hawaii, soil samples were processed from field trials investigating effects of cover crops, living mulches and varying tillage practices on nematode populations in the soil. Tall fescue is a widely planted forage and turfgrass, and an endophytic fungus growing in this plant improves plant vigor and resistance to pathogens. Root extracts from an endophyte-associated tall fescue cultivar that is resistant to root-knot nematodes were fractionated by an ARS chemist in Michigan, and the fractions were tested for activity against nematodes. Identification of chemical constituents that play a role in suppression of root-knot nematodes will contribute to optimizing use of a tall fescue pre-plant ground cover in peach orchards. Nematotoxicity was also found with natural products that were tested as solutions, extracts and/or powdered material for activity against nematodes. These investigations are important for enhancing or developing methods for managing plant-parasitic nematodes and improving crop yields.
Accomplishments
1. Soybean root chemicals cause young nematodes to lose control. Plant-associated nematodes (roundworms) cause billions of dollars in losses to crop plants in the United States and around the world each year. Successful management of nematodes in the field requires knowledge of the interactions between plants and nematodes found in the soil. ARS scientists in Beltsville, Maryland, discovered that soybean-derived chemicals had surprising behavioral effects on the infective-stage juveniles of the soybean cyst nematode. While soybean root extracts contain attractants, as expected, ARS scientists discovered, in laboratory experiments, that roots also contain factors causing abnormal and erratic behaviors, rendering infective juveniles unable to control directional movement. This behavior can eliminate the ability of the nematodes to infect host plants. These root chemicals appear to be small, stable molecules that should provide useful materials for scientists developing precision treatment strategies for use by growers seeking to decrease synthetic chemical use in controlling plant-parasitic nematodes for crop protection.
2. Grass extract repels plant-infecting nematodes. Plant-associated nematodes (roundworms) cause billions of dollars in losses to crop plants in the United States and around the world each year. Successful management of nematodes in the field requires knowledge of the interactions between plants and nematodes found in the soil. ARS scientists in Beltsville, Maryland, discovered that vetivergrass, an economically important plant in many countries and a source of a widely used plant oil, also produces compounds active against root-knot nematodes. In laboratory assays, vetivergrass root and shoot extracts repelled juvenile nematodes (the infective stage on plant roots), and also caused juvenile mortality. Vetiver oil was not active in these studies, indicating that the extracts are better sources of compounds toxic to nematodes. Understanding the plant chemistry will aid in identification of natural compounds with potential to act as biologically based nematicides, and the potential use of vetivergrass by growers as a mulch for managing nematodes.
Review Publications
Leslie, A.W., Wang, K., Meyer, S.L., Marrahatta, S., Hooks, C.R. 2017. Influence of cover crops on arthropods, free-living nematodes, and yield in a succeeding no-till soybean crop. Applied Soil Ecology. 117-118:21-31. https://doi.org/10.1016/j.apsoil.2017.04.003.
Masler, E.P. 2018. Characterisation of the effects on proteases of Heterodera glycines and Meloidogyne incognita second-stage juveniles by inhibitors obtained from cysts of H. glycines. Nematology. 20(1):461-470. https://doi.org/10.1163/15685411-00003151.
Masler, E.P., Perry, R.N. 2018. Hatch, survival and sensory perception. Cyst Nematodes. Oxforshire, UK: CAB International. p. 44-73.
Wang, C., Masler, E.P., Rogers, S.T. 2018. Responses of Heterodera glycines and Meloidogyne incognita infective juveniles to root tissues, root exudates, and root extracts from three plant species. Plant Disease. https://doi.org/10.1094/PDIS-09-17-1445-RE.
Wen, Y., Chitwood, D.J., Vinyard, B.T., Wei, B., Meyer, S.L.F. 2017. Suppression of Meloidogyne incognita by extracts and powdered fruits of Gleditsia sinensis (Chinese honeylocust). Nematropica. 47(2):155-164.
