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United States Department of Agriculture

Agricultural Research Service

Research Project: MOLECULAR AND MORPHOLOGICAL SYSTEMATICS AND IDENTIFICATION OF IMPORTANT PLANT PARASITIC NEMATODES
2012 Annual Report


1a.Objectives (from AD-416):
1) Discover, refine, and implement improved microscopic, molecular, and software tools to modernize classification and improve predictive features for plant-parasitic and other agriculturally important nematodes; and.
2)Discover new nematode species, new host associations, and new geographic occurrences among the many nematodes sent to the Nematology Laboratory for identification by various customers.


1b.Approach (from AD-416):
1) Adapt and test recently discovered and potentially promising light and scanning electron microscopic methods to determine if visualization of diagnostically important critical features can be improved in resolution and consistency. Characterize new agriculturally important nematodes with expanded or novel morphological and molecular diagnostic characters for the development of improved diagnostic keys and phylogenetic trees. Identify and prioritize, using phylogenetic methods, potential molecular control targets based on physiologically important peptides within diverse nematodes having analogous phenotypes; and.
2)Characterize unknown or important nematodes by morphology, molecular biology and host range; and continue to computerize and curate the USDA Nematode Collection.


3.Progress Report:
This is the final report for project 1255-22000-249-00D, which terminated in March, 2012. Plant-parasitic nematodes cause billions of dollars of crop losses each year in the United States and often are quarantine pests requiring immediate identification to protect U.S. agriculture. Therefore, the identification of new species of nematodes and the development of new methods to rapidly and accurately identify nematodes are urgently needed by researchers, regulators, diagnosticians and growers to deliver the safest, most effective possible plant disease controls and regulatory decisions. To this end, ARS researchers have described new species of root-knot, cyst, lesion, stunt nematodes, and fungus- and insect-associated nematodes of importance to agriculture. Among these is a new corn cyst nematode that had escaped previous detection because the smaller cysts passed through the standard size sieves typically used for cyst extraction from soil. Comprehensive diagnostic keys for identification of root-knot nematodes and coffee lesion nematodes, and updated keys of species related to two plant-associated fungus-feeding nematode genera were published and are being used by scientists worldwide to identify nematode species.

New discoveries of various plant-parasitic nematode species were recorded for the first time in U.S. states and other countries 3 and 12 times, respectively. One of the most important of these detections was the sting nematode, which was known to damage turf and soybean plants throughout the southeastern United States but was recently described by us from Delaware for the first time in association with dead soybean plants. As a result of intense interest in potato cyst nematode in the western United States, new geographic locations for these and other cyst nematodes and related genera were discovered in several states. These results facilitated the export of U.S. potatoes and the formal removal of thousands of acres of Idaho potato fields from their previous, regulated status.

Nematode DNA sequences of populations and species using standard and newly introduced molecular markers were generated for identification of nematode species and for the creation of molecular family trees and the evaluation of the utility of anatomical characters in these trees. These evaluations included an assessment of the many tail forms observed within a group of plant-parasitic nematodes known as the stunt nematodes. The results indicated that many of the names previously used by scientists for groups of stunt nematodes are not consistent with the molecular trees and may not be valid. Similarly, a molecular framework used to evaluate appendages of the female reproductive tract across all groups of nematodes demonstrated the differences in these appendages, unreliability for identification, and almost exclusive presence in parasitic nematode species versus other types. These discoveries are being used by diagnosticians, extension and regulatory personnel throughout the world to accurately diagnose crop diseases and select appropriate controls for a wide variety of nematode pests.


4.Accomplishments
1. Building the USDA Nematode Collection. The researchers and extension personnel that identify nematodes need a source of nematode reference specimens to assure that identifications are accurate. The USDA Nematode Collection at Beltsville, Maryland, is the most important repository of nematode reference specimens in the world. Curatorial services and maintenance are constantly needed to improve the quality and breadth of the Collection. Therefore, scientists at the Nematology Laboratory have created a total collection of 44,371 slides and vials, loaned dozens of slides and vials containing valuable nematode specimens to scientists around the world to enable them to perform accurate nematode identifications, and created a Web-accessible database of 38,404 records available to the public. Nematologists, other researchers and regulatory personnel throughout the world are using the specimens and related information in the Collection as essential aids in nematode identification, regulation and research.


Review Publications
Carta, L.K., Skantar, A.M., Handoo, Z.A. 2011. Molecular rDNA phylogeny of Telotylenchidae Siddiqi, 1960 and evaluation of tail termini. Journal of Nematology. 42(4):359-369.

Carta, L.K., Skantar, A.M., Handoo, Z.A., Baynes, M.A. 2011. Supplemental description of Paraphelenchus acontioides Taylor and Pillai, 1967 (Tylenchida: Paraphelenchidae), with ribosomal DNA trees and a morphometric compendium of female Paraphelenchus. Nematology. 13(8):887-899.

Fraedrich, S.W., Cram, M.M., Handoo, Z.A., Zarnoch, S.J. 2012. Influence of Tylenchorhynchus ewingi on growth of loblolly pine seedlings, and host suitability of legumes and small grains. Nematology. 14(4):417-425.

Last Modified: 12/24/2014
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