Rev 11/19/2019

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            Xiphinema (Cobb, 1913)

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Morphology and Anatomy:

Xiphinema is a very large, diverse and complex group of nematode species.  Morphological identification in this group is complex due to overlapping morphometrics and the sharing of many morphological characters. Reliable diagnostic methods are needed to enable distinguishing between species for management, quarantine or regulatory purposes.

The genus may be divided into the americnum  and non-americanum lineages. The americanum lineage consists of around 55 nominal species and cryptic species, many of which are morphologically indistinguishable, and the non-americanum groups of more than 200 more-or-less distinguishable species.

General Characteristics of the Genus:

 Odontostyle is long, connected to lining of cheilostome by a cuticular membrane that becomes variously folded, with refractory qualities - the "guiding ring." 

Species in the genus Xiphinema are relatively large nematodes, 2 to 3 mm in length.  The genus is characterized by the presence of a very long odontostyle or spear (stylet).  The spear and its extension are approximately 150 µm or more in length.

In Xiphinema, the guiding ring is located near the base of the odontostyle, just before the junction with the odontophore.

A flanged odontophore is characteristic of Xiphinema.

In Longidorus, the guiding ring is located 2 lip region widths from the anterior end; no flanges occur on the posterior end of  the odontophore.

Xiphinema has a 2-part esophagus typical of most Dorylaimida, with a slender anterior part and swollen glandular and muscular posterior bulb.

 The cross-sectional configuration of the stylet is cylindrical and the cross-section of the odontophore is tri-radiate as in the esophagus.  The esophagus has a tri-questrous lumen.

Males have paired pre-anal papillae and a ventromedian row of supplementary papillae.  The number and arrangement of these papillae are of importance in distinguishing species.

Males have paired spicules, but no gubernaculum; males have no bursa.

Females of Xiphinema have one or two ovaries.  The ovaries, when both occur, are opposed and reflexed.

Body size range for the species of this genus in the database - Click:


Identification of Species of Xiphinema

Loof and Luc (1990) recognized 172 valid species of Xiphinema by that time and more have been added since. They developed a polytomous key which was split into eight groups on the basis of development of the anterior female genital branch, uterine differentiation and tail shape.  The groups are distinguished by the following criteria:

Code A: type of female genital tract,  the comparative development and structure of the two female genital branches.

Code A1: the anterior genital branch is absent: the ovojector is generally symmetrical but may also be somewhat asymmetrical anteriorly, the vagina is directed slightly backward (X. brasiliense). The vulva is usually anterior (C = ± 30).

Code A2: the anterior uterus may be as long as the posterior one (X. surinamense, X. filicaudatum, X. dimidiatum) but is usually reduced in length and width. The oviduct is greatly reduced to a mass of cells in which generally no lumen or structure can be recognized. The anterior ovary is absent.

Code A3: all the components of the anterior branch are present, but greatly reduced in comparison to those of the posterior branch).

Code A4: there are two fully, equally developed genital branches.

Code A1: X. brasiliense (A), X. radicicola (B)

Code A2: X. longicaudatum (C,D), X. krugi (E,F), X. costaricense (G,H), X. filicaudatum (I)

Code A3: X. hygrophilum (J)

Drawings from Loof and Luc (1990)

Code B: Uterine differentiation.

Code B1: the Z-organ which lies at the junction of the pars dilatata uteri and the distal, more or less straight, part of the uterus is rather well separated from these sections and has a heavy wall composed of strong circular muscles; the lumen has a conspicuous refringent lining which is regularly longitudinally folded; and a relatively low number (3-5) of yellowish, often angular, apophyses protrude into the lumen.

Code B2: the pseudo-Z-organ is found in the same place as the Z-organ but is less well structures; the wall is thinner, the muscles are weaker or almost absent; the lining is thin, its longitudinal folding is often difficult to observe. The apophyses are rarely angular (X. pini) and vary in shape: they appear as composite bodies with a clear central globular part surrounded by small, less translucent globules (e.g. X. diversicaudatum); simple globular bodies (X. marsupilami, X. basiri) of variable diameter.

Code B3: uterine spines are present either all over the length of the tubular part of the uterus (X. spinuterus) or only in the part close to the uterine pouch (X. xenovariabile). They are of variable length and density, but are always directed away from the vagina. In some species both spines and pseudo-Z organ are present (e.g. X. malagasi).

Code B1: X. ifacolum (A), X. ebriense (B)

Code B2: X. pini (C), X. diversicaudatum (D), X. turcicum (E), X. basiria (F), X. ingens (G), X. marsupilami (H)

Code B2/3: X. malagasi (I)

Code B3: X. spinuterus (J)

Drawings from Loof and Luc, 1990

Notet: (1) uterine differentiation appears linked to the presence of two complete female genital branches, the only exception being X. dimidiatum in which the anterior branch is reduced and the posterior one contains uterine spines; and (2) the presence of a Z- or pseudo-Z-organ is more frequent among species having numerous males.

Code C: Female tail shape is one of the most variable characters in the genus. The various tail shapes can be grouped into:

Codes C1-C4:  long filiform to conical shape; the shortest tails (C4) may be somewhat digitate

Code C1: X. spinuterus (A)

Code C2: X. bergeri (B), X. douceti (C), X. nigeriense (D), X. insigne (E), X. attarodorum (F), X. clavicaudatum (G)

Code C2/3: X. elongatum (H,I)

Code C3: X. ifacolum (J), X. longidoroides (K)

Code C3/4: X. coxi (L), X. setariae (M)

Code C4: X. basiri (N)

Drawings from Loof and Luc, 1990

Codes C5-C8:  short, more or less rounded to perfectly hemispherical; sometimes provided with a short peg (C5), or a long one (C8)

Code C5: X. mammallatum (A), X. thorneanum (B), X. brasiliense (C).

Code C6A: X. melitense (D), (E.F)

Code C6B: X. bacaniboia (E), X. surinamense (F)

Code C7A: X. guirani (G)

Code C7B: X. porosum (H), X. hygrophilum (I)

Code C8: X. rotundatum (J)

Drawings from Loof and Luc, 1990

 Tail shapes are characterized as:

Code C1: Tail long, attenuated or filiform (c' over 7.5)

Code C2: Tail long (c' between 2.5 and 7.5), conical or with clavate terminus

Code C3: Tail regularly short conical (c' at most 2.5), i.e. tapering uniformly to narrowly rounded or acute terminus; or slightly subdigitate

Code C4: Tail short conical (c' at most 2.5), distinctly digitate

Code C5: Tail conical to hemispherical with a terminal peg, mucro or bulge

Code C6: Tail broadly convex-conoid, i.e. tapering to broadly rounded terminus with main curvature on dorsal contour, the ventral one being almost straight

Code C7: Tail regularly hemispherical, i.e. ventral and dorsal curvatures equal

Code C8: Tail conical rounded, with very long clavate peg

Code D: coefficient c' – ratio of tail length to anal body diameter

Code D1:  >7.5

Code D2: 5.1-7.5

Code D3: 2.6-5.0

Code D4: 1.6-2.5

Code D5: 1.1-1.5

Code D6: <1.0

Code E: coefficient V – position of vulva (% body length)

Code E1: <30

Code E2: 30-34

Code E3: 35-39

Code E4: 40-44

Code E5: 45-49

Code E6:  >50

Code F: L (body length)

Code F1: <1.5 mm

Code F2: 1.5-2.4 mm

Code F3: 2.5-3.4 mm

Code F4: 3.5-4.4 mm

Code F5: >4.5 mm.

Code G: s spear length (odontostyle+odontophore length)

Code G1:  <150 μm

Code G2:  150-199 μm

Code G3:  200-249 μm

Code G4:  >250 μm

Code H: Shape of anterior part of body (note, body must be in lateral position to avoid confusing amphid apertures as constrictions)

Code H1: no constriction between head region and body, continuous outline

Code H2: intermediate constriction between head and body

Code H3: very conspicuous constriction between head and body


Code H1: X. hygrophylum (A), X. stenocephalum (B)

Code H2: X. elongatum (C,D), X. coxi (E,F), X. insigne (G), X. ingens (H)

Code H3: X. conurum (I), X. pachydermum (J)

Drawings from Loof and Luc, 1990

Code I: (female body posture when killed)

Code I1: Body straight or nearly so

Code I2: Body weakly curved

Code I3: Body hook-shaped, or C- or J-shaped

Code I4: Body spiral-shaped

Code J: (tail shape of 4th stage juvenile)

Same divisions as for Code C

Code K: (tail shape of 1st stage juvenile)

Same divisions as for Code C

Code L: Presence or absence of males (often correlated with presence or absence of sperm in the female genital tract)

Code L1: Unknown or very rare (female generally devoid of sperm)

Code L2: Abundant (female generally provided with sperm).

Using the Polytomous Key of Morphotypes

The characteristics corresponding to each letter of the code are observed, measured or calculated; each of them is allocated the corresponding figure according to the preceding paragraph (the 'new code').
These figures are put on a strip of paper, so that each corresponds to the column of each letter. For example, in the following combination:

4 2 4 5 5/6 3 2/3 1/2 3 3 - 2

The figures under Codes A and B give the morphotype group of the species, this case group 5 (Codes A$ and B2):

On the list under Group 5, the strip of paper is moved from the top of the lattice until a species is found in which the figures correspond  to those on the strip, in this case X. natalense:

Group 5 - Code Sequences (some examples)
Species A B C D E F G H I J K L
X. paraitaliae 4 2 2 3 3/4 3/4 2/3 2 3 2 - 1
X. marsupilami 4 2 2 1 4/5 4 4 2 1 - - 2
X. meridianum 4 2 3 4/5 4/5/6 3/4 2 2 3 3 - 1
X. natalense 4 2 4 5 5/6 3 2/3 1/2 3 4 - 2
X. diversicaudatum 4 2 4/5 5 3/4/5 4/5 3 2 3 5 1 2

 For each column, only one identical figure is needed; in the example chosen, for character G (spear length) the code is 2/3 because the spear length range of the species (197-204 µm) overlaps the crieria for Codes G2 and G3.
If there is no identity for all the letters in any horizontal line, the specimens being identified may represent an undescribed species.  Here molecular tools will be important to confirm differences from other species.

 As emphasized by Loof and Luc (1990), the eight morphotype groups have no taxonomic value and do not infer phylogenetic relationships.  Rather, they assemble the known species into groups that facilitate further identification based on additional characters.

Refer to Loof and Luc, 1990 for a complete list of species in each morphotype group as of 1990.  Others have been charecterized since then, codes for some are provided in Loof and Luc (1993) and Loof et al. (1996).

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Members of the genus occur worldwide.

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 Economic Importance:

Many species ar important parasites of plants, including many agricultural crops. 

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Feeding Habit:

 Ectoparasites; feed along root, including root tips.  Species of Xiphinema feed at root tips and along the length of young roots. Feeding along roots produces symptoms similar to those caused by other cortical feeding nematodes (disintegration of the cortex); those that feed at root tips produce very different symptoms, including root-tip galling and stunting.

Xiphinemabacter is an endosymbiont.

The pathogenicity of X. index is well-defined, but that of the other species has not been studied, and several are known only from survey data (Raski, 1988). Xiphinema index is a migratory ectoparasite. All stages feed at the root tip. The odontostyle penetrates deep into the meristematic region of the root tip where secretions of the esophageal glands result in cell hypertrophy and thickening. Kirkpatrick et al. (1965) showed top and root reductions of grape by 65 and 38% respectively in grape pot tests with X. index.

Xiphinema diversicaudatum also feeds at the root tip and causes galling. In contrast, X. americanum sensu stricto feeds behind the root tip and has not been associated with root tip galling.

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 Many species of Xiphinema have wide host ranges.

For an extensive host range list for this genus, click
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Life Cycle:

For Ecophysiological Parameters for this genus, click 

 Relatively little critical biological and ecological work has been done on this important genus - some species are difficult to maintain in greenhouse cultures, e.g. X. americanum, others apparently have a very long life-cycle, e.g.,  X. diversicaudatum.. All stages occur in the soil.

Eggs, from which first-stage juveniles emerge, are deposited singly in water films around soil particles and are not enclosed in an egg-mass. There are three or four juvenile stages and sexually mature adults. Males are rare in most species and are apparently unnecessary for reproduction.

Life cycle of Xiphinema

The relationship between odontostyle length and body length is characteristically linear with the relacemeny odontostyle for the next life stage longer than that of the current life stage.
The linear relationship is well illustarted in X. zagrosense ( Ghemi et al., 2012)

Endosymbiont Bacteria

Palomeres-Rius et al (2016) screened 124 plant-feeding nematode populations for the presence of bacterial endosymbionts; that is, bacteria living within the body of the nematode. 
Potential bacterial endosymbionts were only detected in species of Xiphinema, particularly in species of the X. americanum (sensu lato) group.

One group of 16S rRNA sequences was related to ‘Candidatus Xiphinematobacter’ and a second to the bacterial family Burkholderiaceae, which includes fungal and plant endosymbionts.

The study suggests a highly specific symbiotic relationship and a high degree of phylogenetic congruence and long-term evolutionary association between hosts and endosymbionts.

The bacterial endosymbionts are transmitted vertically to progeny.  They are observed to colonize the ovary wall of females of Xiphinema species, they apparently invade developin oocytes  and are seen in uninucleate eggs in the uterus.  They become associated with intestinal epithelium during nemattode development and then with the overy in adult females (Palomares-Rius, 2016; Vandekerckhove et al., 2002; Brown et al., 2015).

Endosymbionts may have effects that range from parasitism (harmful to the host), through commensalism (neutral effects) to mutualism (beneficial to host and enosymbiont).  The effects of the realtionships between the endosymbionts and Xiphinema spp. is unknown at this time)s.  In the latter case, both host and endosymbiont would benefit from the realtionship.Although the nat

There are other examples of bacterial endosymbionts in nematodes.  In many cases their roles in the biology of the nematode are unknown (Palomares-Rius et al, 2016), for example:

  1. A mutualistic relationship with Wolbachia which provides essntial metabolites for protein synthesis (Werren et al., 2008; Foster et al., 2005).
  2. Associations between the insect-pathogenic bacteria Photorhabdus and Xenorhabdus is necessary for completion of the life cycle of Heterorhabditis and Stienernema (Ruby. 2008).

  3. Detection of Wolbachia in the burrowing nematode Radopholus similis  and R. arabocoffeae (Haegeman, et al. 2009).

  4. Verrucomicrobia has been detected in theXiphinema americanum group (Vandekerckhove et al., 2002).

  5.  Bacteroidetes has been detected in populations of Heterodera glycines and Globodera rostochiensis (Noel & Atibalentja 2006).


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      Species of Xiphinema are primarily problematic in biennial and permanent crop situations. Except for damage to emerging seedlings, they are seldom of major importance in annual crops as they rarely attain high population levels when soil is frequently tilled. However, in the case of species that are vectors of plant viruses, the damage casused by the viruses may be independent of the abundnace of nematodes.

Feeding along roots produces symptoms similar to other cortical feeders  (distintegration of cortex); those that feed at root tips produce very different symptoms, i.e., root stunting.  There is also ample evidence that the nematode injects substances into roots which causes root swelling.  Damage to roots causes foliage to become stunted.

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      Control of Xiphinema spp. on many annual crops may not be of major importance since species of this nematode seldom attain high population levels when soil is frequently tilled.

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Copyright © 1999 by Howard Ferris.
Revised: November 19, 2019 .