Cluster Analysis of Longidorus Species (Nematoda: Longidoridae), a New Approach in Species Identification

Hierarchical cluster analysis based on female morphometric character means including body length, distance from vulva opening to anterior end, head width, odontostyle length, esophagus length, body width, tail length, and tail width were used to examine the morphometric relationships and create dendrograms for (i) 62 populations belonging to 9 Longidorus species from Arkansas, (ii) 137 published Longidorus species, and (iii) 137 published Longidorus species plus 86 populations of 16 Longidorus species from Arkansas and various other locations by using JMP 4.02 software (SAS Institute, Cary, NC). Cluster analysis dendograms visually illustrated the grouping and morphometric relationships of the species and populations. It provided a computerized statistical approach to assist by helping to identify and distinguish species, by indicating morphometric relationships among species, and by assisting with new species diagnosis. The preliminary species identification can be accomplished by running cluster analysis for unknown species together with the data matrix of known published Longidorus species.     

Longidorus biformis n. sp. and L. glycines n. sp. (Nematoda: Longidoridae): Two Amphimictic Species from Arkansas

Two new amphimictic species of Longidorus were found in Arkansas. Longidorus biformis n. sp., found in the rhizosphere of hardwood trees along streams in sandy soil in 14 Arkansas locations, is characterized by its long body (5.42-9.50 mm), wide expanded flattened head end, head width 20.0 to 26.0 µm, odontostyle 96 to 125 µm, guide ring 29 to 38 µm posterior to the anterior end, elongate conoid tail, and c'' = 0.9-2.1. Females with 2 to 11 vetromedian supplement-like structures were found in 2 of 14 populations of this new species. Longidorus biformis n. sp. is closest to L. seinhorsti Peneva, Loof &Brown, 1998 and L. closelongatus Stoyanov, 1964. Among North American species it is closest to L. glycines n. sp. A distinguishing feature of L. biformis n. sp. is the presence of supplement-like organs in some females. Longidorus glycines n. sp., found in soybean microplots at the Main Research Station, Fayetteville, Arkansas, is characterized by its long body (6.14-8.31 mm), wide offset flattened head end, head width 20.3 to 23.3 µm, odontostyle 87.3 to 99.5 µm, guide ring 22.3 to 26.4 µm posterior to the anterior end, short conoid tail with rounded terminus, and c'' = 0.9-1.4. Longidorus glycines n. sp. is closest to L. lusitanicus Macara, 1985. Among North American species it is close to L. biformis n. sp., L. breviannulatus Norton and Hoffman, 1975, and L. crassus Thorne, 1964. Both new species are believed to have four juvenile stages; the first stage was not found for L. biformis n. sp.     

Longidorus paravineacola n. sp. (Nematoda: Longidoridae), a New Species from Arkansas

Longidorus paravineacola n. sp., described herein, was found in a survey of longidorids of Arkansas. It is a parthenogeneticspecies characterized by its long body (6.68-9.85 mm); slightly expanded and rounded head, head width 21-27 µm; odontostyle length 95-114 µm; guide ring 28-37 µm posterior to the head end; short rounded tail, and c'' = 0.6-1.0. Longidorus paravineacola n. sp. is similar to the amphimictic species L. vineacola Sturhan &Weischer, 1964; L. balticus Brzeski, Peneva &Brown, 2000; L. kuiperi Brinkman, Loof &Barbez, 1987; and parthenogenetic species L. crassus Thorne, 1974, which also occurred in the type locality.     

Descriptions of Three New Longidorus Species from Alaska (Nematoda: Longidoridae)

Three new Longidorus species, L. alaskaensis n. sp., L. paralaskaensis n. sp., and L. bernardi n. sp., are described from specimens collected near Fairbanks, Alaska. Longidorus alaskaensis differs from all species of Longidorus by the presence of a caecum-like structure situated at the reflex of the oviduct. Longidorus paralaskaensis most closely resembles L. alaskaensis n. sp., L. crassus Thorne, L. picenus Roca, Lamberti &Agostinelli, and L. silvae Roca, differing from the last three of these species by having a parallel vs. a tapered lip region, and from all four by having a more narrowly rounded tail tip. Longidorus paralaskaensis differs from L. alaskaensis by having a longer odontostyle (119-128 vs. 110-118 μm) and by lacking the caecum-like structure found at the reflex of the oviduct. Longidorus bernardi n. sp. most closely resembles L. mirus Khan, Chawla &Seshadri, from which it differs by having a longer tail with a more acutely rounded tip, a longer body length (3.5-4.6 vs. 3.0-3.6 μm), and a larger c'' value (1.6-1.8 vs. 1.3-1.6). Longidorus bernardi differs from L. sylphus Thorne, L. africanus Merny, L. auratus Jacobs &Heyns, and L. conicaudatus Khan by having a slightly expanded lip region vs. a lip region with parallel body walls and a more finely rounded tail tip.     

Longidorus grandis n. sp. and L. paralongicaudatus n. sp. (Nematoda: Longidoridae), Two Parthenogenetic Species from Arkansas

Two new parthenogenetic species of Longidorus were found in Arkansas. Longidorus grandis n. sp. is characterized by its body (5.80-8.24 mm), slightly offset head, head width 20-27 µm, odontostyle 86-100 µm, guide ring 26-35 µm posterior to the anterior end, short conoid to mammiliform tail. Longidorus grandis n. sp. is similar to L. vineacola Sturhan &Weischer, 1964; L. lusitanicus Macara, 1985; L. edmundsi Hunt &Siddiqi, 1977; L. kuiperi Brinkman, Loof &Barbez, 1987; L. balticus Brzeski, Peneva &Brown, 2000; L. closelongatus Stoyanov, 1964; and L. seinhorsti Peneva, Loof &Brown, 1998. Longidorus paralongicaudatus n. sp. is characterized by its body length (2.60-5.00 µm), anteriorly flattened and offset head region 13-18 µm wide, odontostyle length 92-127 µm, guide ring 21-30 µm posterior to the anterior end, tail elongate-conical, and c'' = 1.2-2.6. Longidorus paralongicaudatus n. sp. most closely resembles L. longicaudatus Siddiqi, 1962; L. socialis Singh &Khan, 1996; L. juvenilis Dalmasso, 1969; and L. curvatus Khan, 1986.     

Phylogenetic Relationships and Genetic Variation in Longidorus and Xiphinema Species (Nematoda: Longidoridae) Using ITS1 Sequences of Nuclear Ribosomal DNA

Genetic analyses using DNA sequences of nuclear ribosomal DNA ITS1 were conducted to determine the extent of genetic variation within and among Longidorus and Xiphinema species. DNA sequences were obtained from samples collected from Arkansas, California and Australia as well as 4 Xiphinema DNA sequences from GenBank. The sequences of the ITS1 region including the 3'' end of the 18S rDNA gene and the 5'' end of the 5.8S rDNA gene ranged from 1020 bp to 1244 bp for the 9 Longidorus species, and from 870 bp to 1354 bp for the 7 Xiphinema species. Nucleotide frequencies were: A = 25.5%, C = 21.0%, G = 26.4%, and T = 27.1%. Genetic variation between the two genera had a maximum divergence of 38.6% between X. chambersi and L. crassus. Genetic variation among Xiphinema species ranged from 3.8% between X. diversicaudatum and X. bakeri to 29.9% between X. chambersi and X. italiae. Within Longidorus, genetic variation ranged from 8.9% between L. crassus and L. grandis to 32.4% between L. fragilis and L. diadecturus. Intraspecific genetic variation in X. americanum sensu lato ranged from 0.3% to 1.9%, while genetic variation in L. diadecturus had 0.8% and L. biformis ranged from 0.6% to 10.9%. Identical sequences were obtained between the two populations of L. grandis, and between the two populations of X. bakeri. Phylogenetic analyses based on the ITS1 DNA sequence data were conducted on each genus separately using both maximum parsimony and maximum likelihood analysis. Among the Longidorus taxa, 4 subgroups are supported: L. grandis, L. crassus, and L. elongatus are in one cluster; L. biformis and L. paralongicaudatus are in a second cluster; L. fragilis and L. breviannulatus are in a third cluster; and L. diadecturus is in a fourth cluster. Among the Xiphinema taxa, 3 subgroups are supported: X. americanum with X. chambersi, X. bakeri with X. diversicaudatum, and X. italiae and X. vuittenezi forming a sister group with X. index. The relationships observed in this study correspond to previous genera and species defined by morphology.     

Distribution and Morphology of Longidorus breviannulatus Norton &Hoffman, 1975 and Longidorus fragilis Thorne, 1974 (Nematoda: Longidoridae) from North America

In a survey of ecotypes for longidorids, primarily from the rhizosphere hardwood trees growing in sandy soil along stream banks, 828 soil samples were collected from 37 Arkansas counties in 1999-2001. Eight populations of Longidorus breviannulatus were identified from the Arkansas survey samples. A total of 19 populations from California, Illinois, Iowa, Kansas, Michigan, Nebraska, New Jersey, New York, and Wisconsin were identified from the collection of the second author. A few males were found in New York and Nebraska populations and are described herein. Seven populations of L. fragilis were identified in the Arkansas survey samples, and one population was found from Indiana. Four juvenile stages of L. fragilis are present, and data are given for them herein.     

Descriptions of Three New Longidorus Species from Slovakia (Nemata: Longidoridae)

Three new Longidorus species from Slovakia are described. Longidorus carpathicus n. sp. most closely resembles Longidorus silvae but differs by having a longer odontostyle, odontophore, and total stylet; smaller a and c ratios; and longer distance to the guide ring. This new species also resembles L. picenus, L. macrosoma, and L. major but differs by having a narrower lip width. It further differs from L. picenus by having a longer odontostyle and smaller c ratio, and by lacking males; from L. macrosoma by having a longer odontostyle, smaller c ratio, by lacking males, and a more pronounced J1 tail peg; and from L. major by having a shorter body length, longer odontostyle, longer odontophore, and longer J1 tail peg. Longidorus piceicola n. sp. most closely resembles L. eridanicus, from which it differs by having a greater lip width, longer tail, smaller c ratio, larger c'' ratio, shorter hyaline tail length, and a conically rounded vs. hemispherical tail. This new species differs from L. cylindricaudatus by having a larger lip width, longer odontostyle and odontophore, and a greater distance to the guide ring; from L. nevesi by having a shorter body length, longer odontostyle, larger c'' ratio, and shorter hyaline tail length. Longidorus juglansicola n. sp. most closely resembles L. athesinus but differs by its longer body, wider lips, and larger a and c ratios. It closely resembles L. vineacola but differs by its shorter body length, smaller c ratio, and an almost parallel lip outline vs. an expanded lip outline; from L. lusitanicus by a longer odontophore and tail, and an almost parallel lip outline vs. an expanded lip outline.     

Redescription of Three Ektaphelenchus Species (Nematoda: Aphelenchina)

Three Ektaphelenchus species with unusual spicules are redescribed. Ektaphelenchus obtusus and E. riograndensis are redescribed from newly discovered material in the collection of the USDA Forest Service RMRS. Lectotype slides are designated for both species. Ektaphelenchus obtusus is characterized by a set-off head, lips of unequal size, double rows of oocytes and spermatocytes, and a hooked spicule terminus. Ektaphelenchus riograndensis is distinguished by a rounded head with six equal lips, and spicules with a large, rounded apex, and recurved terminus. A bursa and gubernaculum are absent in both species. Ektaphelenchus scolyti is redescribed from type material deposited in the collection of Rothamsted Experimental Station. It is characterized by a well set-off head, double rows of oocytes and spermatocytes, and spicules with a hooked terminus. A bursa and gubernaculum are absent.     

First report of Xiphinema brevicolle Lordello et Costa, 1961 (Nematoda, Longidoridae) in Japan

Mixed populations of Xiphinema americanum-group species were detected from a root zone soil sample of Japanese holly, Ilex crenata, during a survey for plant-parasitic nematodes of commercial ornamental plant nurseries in Chiba Prefecture, Japan. From the result of the morphological study, the species were identified as Xiphinema brevicolle and Xiphinema sp. This is the first record of Xiphinema brevicolle in Japan. Morphometrics of Xiphinema brevicolle generally agree with those of the type specimens and the topotype specimens. Xiphinema sp. morphometrically resembles Xiphinema paramonovi except for tail length. The mitochondrial COI region, the nuclear 18S rDNA and the nuclear large subunit rDNA D2/D3 region of the species were sequenced and compared in the molecular study. For the COI region, PCR primers were newly designed to obtain longer sequences, ca. 900 bp, than previously used. Sequence identities of COI, 18S and D2/D3 regions between these two populations were 84.0-84.1%, 99.9% and 98.1-98.2%, respectively. Phylogenetic analyses of maximum likelihood trees were carried out to compare genetic relationships among the group and some suggestions were made on the Xiphinema brevicolle-subgroup.     

Morphological and Molecular Characterization of Longidorus americanum n. sp. (Nematoda: Longidoridae), a Needle Nematode Parasitizing Pine in Georgia

We describe and illustrate a new needle nematode, Longidorus americanum n. sp., associated with patches of severely stunted and chlorotic loblolly pine, (Pinus taeda L.) seedlings in seedbeds at the Flint River Nursery (Byromville, GA). It is characterized by having females with a body length of 5.4-9.0 mm; lip region slightly swollen, anteriorly flattened, giving the anterior end a truncate appearance; long odontostyle (124-165 µm); vulva at 44%-52% of body length; and tail conoid, bluntly rounded to almost hemispherical. Males are rare but present, and in general shorter than females. The new species is morphologically similar to L. biformis, L. paravineacola, L. saginus, and L. tarjani but differs from these species either by the body, odontostyle and total stylet length, or by head and tail shape. Sequence data from the D2-D3 region of the 28S rDNA distinguishes this new species from other Longidorus species. Phylogenetic relationships of Longidorus americanum n. sp. with other longidorids based on analysis of this DNA fragment are presented. Additional information regarding the distribution of this species within the region is required.     

Taxonomic and Molecular Identification of Mesocriconema and Criconemoides Species (Nematoda: Criconematidae)

Populations of Mesocriconema curvatum, M. kirjanovae, M. onoense, M. ornatum, M. sphaerocephala, M. surinamense, M. vadense, M. xenoplax, and Criconemoides informis from different geographical areas in the continental United States were characterized morphologically and molecularly. A new ring nematode from Washington County, Arkansas, is also described and named Mesocriconema ozarkiense n. sp., This new species is characterized by females with small flattened submedian lobes, lower than or at the same level as the labial disc, vagina straight, very well developed spermatheca without sperm, no more than one anastomoses, L=379-512 μm, V=89-93, stylet length = 49-61 μm, R=107-119, annuli with slightly crenate margins on tail portion and a simple anterior vulval lip. The molecular characterization of M. ozarkiense n. sp. using the ITS rRNA gene sequence and the phylogenesis relationship of this new species with the ring nematodes included in this study are provided.     

A Key and Compendium to Species of the Heterodera avenae Group (Nematoda: Heteroderidae)

A key based on cyst and juvenile characters is given for identification of 12 valid Heterodera species in the H. avenae group. A compendium providing the most important diagnostic characters for use in identification of species is included as a supplement to the key. Cyst characters are most useful for separating species; these include shape, color, cyst wall pattern, fenestration, vulval slit length, and the posterior cone including presence or absence of bullae and underbridge. Also useful are those of second-stage juvenile characteristics including aspects of the stylet knobs, tail hyaline tail terminus, and lateral field. Photomicrographs of diagnostically important morphological features complement the compendium.     

Three New Species of the Super Family Neotylenchoidea (Nematoda: Tylenchida) from Pakistan

Three new species in the super family Neotylenchoidea collected in Pakistan during 1979-80 are described. New species Nothotylenchus gohleni is related to N. affinis Thorne, 1941 but is differentiated by its longer, more robust body with tine cuticular annules, a more posterior vulva, inconspicuous basal knobs of the stylet, and poorly developed metacorpal area. N. geraerti and N. tuberosus are also close to this undescribed species, hut they have a more developed metacorpal area and a larger post uterine sac. Boleodorus zaini n.sp. is distinguished by its excretory pore open at a level with the base of the posterior esophageal bulb and by six distinct lines in the lateral field. Paurodontella sohailai n.sp. is closely related to P. densa (Thorne, 1941) Hussain &Khan, 1967 and P. minuta Hussain &Khan, 1967 but differs from them by its larger body, shape of tail, and seven incisures in the lateral field.     

Taxonomic Notes on Four Species of Panagrellus Thorne (Nematoda: Cephalobidae)

Four populations of Panagrellus redivivus (Linnaeus, 1767) Goodey, 1945, and syntypes of P. dubius Sanwal, 1960, P. redivivoides (Goodey, 1943) Goodey, 1945, P. pycnus Thorne, 1938, P. zymosiphilus (Brunold, 1950) Brunold, 1954, and P. leucocephalus Steiner, 1936 were examined. Additional information on the morphology of spicules and stoma is presented. P. zymosiphilus is synonymized with P. redivivoides and Rühm''s synonymization of P. silusiae and P. leucocephalus with P. redivivus is supported. Lectolypes for P. pycnus and P. redivivoides are designated.