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Title: First report of a new stunt nematode Tylenchorhynchus sp. from a soybean field in North Dakota

item YAN, GUIPING - North Dakota State University
item PLAISANCE, ADDISON - North Dakota State University
item HUANG, DANQIONG - North Dakota State University
item Handoo, Zafar

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2017
Publication Date: 2/5/2018
Citation: Yan, G.P., Plaisance, A., Huang, D., Handoo, Z.A. 2018. First report of a new stunt nematode Tylenchorhynchus sp. from a soybean field in North Dakota. Plant Disease. 102(2):453.

Interpretive Summary: Plant-parasitic nematodes are microscopic worms that attack plant roots and cause an estimated ten billion dollars of crop loss each year in the United States and 100 billion dollars globally. Stunt nematodes are an important problem damaging the roots of many kinds of plants worldwide. One problem with determining the extent of damage to crop plants is that the nematodes present in many areas are not known, such as in North Dakota. This brief report describes how a team of North Dakota State University and ARS scientists identified from a soybean field in Richland County, ND, a new species of stunt nematode by both morphological and molecular means. They also discovered how to distinguish the new species from closely related species with molecular and anatomical features. The results are significant because they represent the only details for identifying this new species. Therefore, this research will be used by scientists, growers, action agencies, and extension agencies involved in nematode research and control.

Technical Abstract: Stunt nematodes in the genus Tylenchorhynchus are common plant-parasitic nematodes, and several species have been reported to damage crops. In 2015 and 2016, eleven soil samples were collected from a soybean (Glycine max) field in Richland County, ND. Nematodes were extracted from soil with the sugar centrifugal flotation method. Nine of the samples contained stunt nematodes, along with root-lesion, spiral, stubby root, and soybean cyst nematodes. The stunt nematodes ranged from 125 to 900 per kg of soil. One soil sample with 600 stunt nematodes per kg of soil was planted with a soybean cultivar Sheyenne in three replicates. After 3 months of growth at 22°C under greenhouse conditions, the stunt nematode population increased to a final density of 1,953 individuals per kg of soil. The reproduction factor of this nematode was 3.26. Soybean roots were rinsed with tap water and brown lesions were observed on the roots. Morphological measurements of adult females (n = 14) included body length (mean = 744.3 µm, range = 622.0-830.0 µm), stylet (21.3, 20.0-22.5), body width (25.1, 23.0-27.5), head end to posterior end of esophageal glands (134.0, 117.0-155.0), anal body width (16.2, 15.0-17.5), tail length (47.0, 38.0-52.0), tail annules (19.9, 16.0-25.0), a (29.6, 25.7-34.0), b (5.5, 5.0-5.8), c (15.8, 13.5-18.1), c' (2.9, 2.6-3.3) and V (52.4%, 50.3-55.2). Morphological measurements of adult males (n = 6) included body length (711.7, 630.0-775.0), stylet (20.8, 20.0-22.5), body width (24.1, 22.5-26.0), head end to posterior end of esophageal glands (130.3, 123.0-135.0), anal body width (15.0, 13.0-18.0), tail length (42.0, 38.0-45.0), a (30.0, 28.1-32.9), b (5.5, 5.1-5.7), c (16.9, 16.4-17.6), c' (2.8, 2.4-3.4), spicule (24.3, 22.5-25.0), and gubernaculum (12.9, 11.0-15.0). DNA was extracted from single nematodes (n = 6) using the Proteinase K method. The D2-D3 expansion domain of 28S rRNA and ITS region of rDNA were amplified and sequenced. The consensus ITS rDNA sequence (Accession No. KY200668, 861 bp) deposited into GenBank had the highest identity of 92% with a T. thermophilus sequence (KJ461594.1) and showed 86% identity with a T. annulatus sequence. The D2-D3 sequence (GenBank Accession No. KY200667, 715 bp) exhibited the highest identity of 98% with a T. thermophilus sequence (KJ461562.1) and showed 96% identity with a T. annulatus sequence. However, the tail of the unknown differs from that of T. thermophilus, and the 71 nucleotide difference in ITS sequence does not support T. thermophilus, although all other morphometric and morphological details fit fine. The tail resembles that of T. crassicaudatus but is not as clavate. No sequence information of T. crassicaudatus is available in GenBank. The tail of the unknown and the nature of the inner two lines of the lateral field with oblique striae resemble T. annulatus, but the sequence data do not support T. annulatus. According to both morphological observations and molecular analyses with the above closely related species, this population from the soybean field in North Dakota represents a new stunt nematode species.