|YAN, GUIPING - North Dakota State University|
|PLAISANCE, ADDISON - North Dakota State University|
|HUANG, DANQIONG - North Dakota State University|
|CHOWDHRY, I - North Dakota State University|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2016
Publication Date: 7/13/2017
Citation: Yan, G.P., Plaisance, A., Huang, D., Chowdhry, I.A., Handoo, Z.A. 2017. First report of the new root-lesion nematode Pratylenchus sp. on soybean in North Dakota. Plant Disease. 101(8):1554. https://doi.org/10.1094/PDIS-04-17-0594-PDN
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. Lesion 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 lesion 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: Root-lesion nematodes (Pratylenchus spp.) are important nematode pests on soybean. In 2015, two soil samples were collected from a soybean field in Richland County, ND. Nematodes were extracted from soil using a sugar centrifugal flotation method, revealing these two samples contained 125 and 350 root-lesion nematodes per kg soil, respectively. In 2016, four soil samples were collected from the same field and all the samples had lesion nematodes ranging from 300 to 2,000. One soil sample with 350 lesion nematodes per kg soil was planted to soybean cultivar Barnes (n = 4). After 15 weeks of growth in a greenhouse room at 22°C, the root-lesion nematode population was found to have increased greatly. The final population density in soil was 1,518 lesion nematodes. Soybean roots were rinsed with water and brown lesions were observed on them. The clean roots were cut into 1-cm segments for nematode extraction using the Whitehead tray method (Whitehead and Hemming 1968). After 48 hours, lesion nematodes were recovered from the root tissues with 25 found per g of fresh roots. Reproduction factor of the nematode was 5.02, indicating that this nematode infects and reproduces well on this soybean cultivar. Morphological measurements of adult females (n = 22) included body length (mean = 484.5 µm, range = 390.0 - 555.0 µm), stylet (17.5, 16.0 - 18.0), body width (21.9, 20.8 - 29.8), head end to posterior end of esophageal glands (118.8, 110.0 - 140.0), anal body width (13.0, 10.0-16.0), tail length (24.4, 20.0 - 30.0), a (23.4, 20.8 - 29.8), b (4.0, 3.2 - 4.8), c (20.2, 16.8 - 24.1), c' (1.9, 1.4 - 2.4) and V (80.2%, 78.0 - 83.0). Morphological measurements of adult males (n = 7) were body length (445.7, 355.0 - 502.0), stylet (16.0, 15.5 - 16.5), body width (18.9, 17.0 - 21.0), head end to posterior end of esophageal glands (109.3, 101.0 - 115.0), anal body width (10.9, 10.0-12.0), tail length (23.1, 20.0 - 25.0), a (23.7, 20.8 - 25.2), b (4.1, 3.2 - 4.8), c (20.0, 16.7 - 21.3), c' (2.1, 1.9 - 2.4), spicule (17.5, 16.0 - 18.5), and gubernaculum (4.5, 4.0 - 5.0). Two regions were characterized by sequencing 28S D2-D3 (Subbotin et al. 2008) and ITS rDNA (Yan and Smiley 2010). DNA was extracted from single nematodes (n=8) from soil and roots (Kumari and Subbotin 2012). The consensus sequence (GenBank Accession No. KX889989, 702 bp) from the 28S had less than 86% similarity with three morphologically closely related Pratylenchus spp. including P. convallariae, P. pratensis, and P. fallax. Sequence (Accession No. KX889990, 1226 bp) from the ITS had less than 82% similarity with P. convallariae and P. fallax. No ITS sequence of P. pratensis is available in the GenBank. The sequence data didn’t support P. convallariae, P. pratensis, or P. fallax. Another closely related species is P. flakkensis, for which there is no sequence information in the GenBank database. However, morphologically it differs from P. flakkensis in several characters such as having a high head, 3 head annules, slightly longer stylet in females, higher vulva % and longer spicule in males. Accordingly both morphological and molecular observations with known and above closely related species indicate that the North Dakota isolate on soybean represents a new lesion nematode species.