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Title: First report of a new, unnamed lesion nematode Pratylenchus sp. infecting soybean 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
item Chitwood, David

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2017
Publication Date: 7/13/2017
Citation: Yan, G.P., Plaisance, A., Huang, D., Handoo, Z.A., Chitwood, D.J. 2017. First report of a new, unnamed lesion nematode Pratylenchus sp. infecting soybean in North Dakota. Plant Disease. 101(8):1555.

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: Lesion nematodes (Pratylenchus spp.) are important pests on soybean. In 2015 and 2016, nematodes in 11 soil samples from a soybean field in Richland County, ND were extracted by sugar centrifugal flotation method (Jenkins 1964). Ten samples contained lesion nematodes from 150 to 875/kg of soil. One sample with 300 lesion nematodes/kg soil was used to inoculate soybean cultivar Barnes (n = 4); after 15 weeks of growth at 22°C in the greenhouse, the Pratylenchus population increased to 460 ± 181 nematodes/kg soil. After rinsing with water, brown lesions were observed on soybean roots. The washed roots were cut into small pieces from which nematodes were extracted with Whitehead tray method (Whitehead and Hemming 1968); after 48 hours, the lesion nematodes recovered amounted to 34 ± 21/g of fresh root. Successful nematode invasion and reproduction were indicated by its reproductive factor of 3.76, calculated by dividing the final population (564 = 460 nematodes/kg soil x 0.5 kg soil/pot + 34 nematodes/g root x 9.835 g root/pot) in both roots and soil by the initial population (150 = 300 nematodes/kg soil x 0.5 kg soil/pot) in soil. Measurements of adult females (n = 20) included body length (mean = 409.0 µm, range = 317.0 - 505.0 µm), stylet (14.9, 12.5 - 17.0), body width (17.4, 14.5 - 22.0), head end to posterior end of esophageal glands (105.0, 80.0 - 125.0), anal body width (10.2, 8.0-13.5), tail length (20.7, 17.5 - 25.0), tail annules (20.0, 15.0 - 25.0), a (23.4, 16.7 - 32.6), b (3.9, 3.2 - 5.0), c (19.5, 17.1 - 22.5), c' (2.1, 1.8 - 2.6) and V (77.6%, 75.3 - 80.3). Morphological data of adult males (n = 4) were body length (429.2, 395.0 - 500.0), stylet (14.0, 12.5 - 15.5), body width (18.6, 17.0 - 21.0), head end to posterior end of esophageal glands (105.0, 100.0 - 110.0), anal body width (9.5, 9.0-10.0), tail length (20.0, 18.0 - 24.0), a (21.2, 20.6 - 29.4), b (4.3, 4.2 - 4.5), c (22.4, 17.7 - 25.6), c' (2.3, 2.2 - 2.4), spicule (17.5, 15.0 - 20.0), and gubernaculum (5.8, 4.5 - 7.5). DNA was extracted from single nematodes (n = 12) from soil and roots. D2-D3 of 28S rRNA (Subbotin et al. 2008) and ITS rDNA (Yan and Smiley 2010) were amplified and sequenced. The ITS rDNA (GenBank Accession KY200666, 981bp) shared 95% sequence identity with P. alleni and low identity (= 87%) with other Pratylenchus spp. The D2-D3 (KY200665, 766bp) had the highest identity of 96% with P. scribneri and 95% identity with P. hexincisus. No sequence of P. gibbicaudatus or P. flakkensis is available in GenBank. This species is very close to P. alleni but differs in having a slightly longer stylet, variations in tail shape, truncate to bluntly or broadly rounded tail with an annulated to occasionally smooth tail terminus, 4-6 lines in lateral field and 2-3 head annules. It is closely related to P. hexincisus, P. gibbicaudatus and P. flakkensis but differs from them by one or more other characters: shape of head, number of head annules, tail shape and V%. It is distinct from the new Pratylenchus sp. reported in a soybean field in North Dakota (Yan et al. 2016). According to both morphological and molecular observations with the above closely related species, this North Dakota isolate on soybean represents a new lesion nematode species.