1a. Objectives (from AD-416):
1) Develop new diagnostic methods for efficient and well-resolved microscopic images of plant-parasitic nematodes. 2) Expand taxonomic representation for existing DNA markers and evaluate new ones to determine the most reliable regions for nematode identification and phylogeny. 3) Determine nematode identities for unknown or emerging agroecological problems involving nematodes for APHIS personnel, state diagnosticians, and ARS and other researchers.
1b. Approach (from AD-416):
1) Advanced microscopy techniques will reveal more detailed features and increase consistency of nematode description for improved diagnosis of described and undescribed nematodes that may damage agriculturally important plants. 2) Expanding ribosomal and Hsp90 gene sequences to more species beyond the relative handful in GenBank, compared to the many known number of morphospecies, will produce more informative family trees that will demonstrate the distribution of plant parasitism for improved pathology prediction. 3) In the process of characterizing new nematode samples, any plant-parasitic or agriculturally important nematode obtained from a customer may be a new species unknown to science or an existing species not known to be present in the United States, another country, a state or a given host.
3. Progress Report:
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 added 247 slides and vials from worldwide sources to create a total collection of 45,025 slides and vials, and entered 231 records of specimens into the computerized database, bringing it to a total of 39,200 records. Nematologists throughout the world are using the specimens and related information in the Collection as essential aids in nematode identification, regulation and research. The colonization mechanisms of microorganisms called endophytes that live within plants are important in agricultural and natural resource management, because endophytes combat plant diseases and often change the toxin levels in some plants. These endophytic microorganisms may benefit or harm plants and livestock. Some nematodes also live endophytically within plant stems or roots, and certain species of nematodes can carry particular fungal or bacterial microorganisms within plants. Therefore identifying and characterizing these endophytic nematodes is important for managing plant diseases and the levels of toxins made by endophytic microorganisms. Scientists at the USDA in Beltsville demonstrated that nematodes isolated from stems of cheatgrass weeds had high-resolution microscopic head-views very similar to a much more commonly encountered species from soil. Another nematode from cultured roots of Idaho pine had a face pattern consistent with the few other species of that genus previously found only in soil. After further anatomical and molecular information is obtained, the discoveries will benefit farmers and rangeland managers who practice plant disease detection, therapy and prevention. Identifying plant-parasitic nematodes through use of DNA molecular markers is important for accurate plant disease diagnosis. However, many species of anatomically described nematodes still have major gaps in their marker representation within genetic databases such as GenBank. Molecular sequences generated in the USDA Beltsville Nematology Laboratory for two plant-parasitic stunt nematode species are the first molecular markers for these types of nematodes. These new sequences will be used by plant disease diagnosticians.
1. New species of cyst nematode. Cyst nematodes are an important group because they damage the roots of many kinds of plants worldwide. We described the anatomical and molecular features of a new cyst nematode that was discovered in soil samples collected during surveys to detect potato cyst nematodes (PCN). This research is significant because the new species shares key anatomical features with two PCN species of regulatory concern, the pale potato cyst nematode and the golden nematode. The newly described species can confound accurate diagnosis of PCN because current molecular tests are not set up to identify it. The morphological and molecular data describing this lookalike species will help scientists, regulators, and extension agencies to more accurately identify and prevent the spread of potato cyst nematodes.
Khan, M.R., Handoo, Z.A., Rao, U., Rao, S.B., Prasad, J.S. 2012. Observations on the foliar nematode, Aphelenchoides besseyi, infecting tuberose and rice in India. Journal of Nematology. 44(4):391-398.