TAXONOMY OF LONGIDORID NEMATODES AND DICHOTOMOUS KEYS FOR THE IDENTIFICATION OF XIPHINEMA AND XIPHIDORUS SPECIES RECORDED IN BRAZIL

TAXONOMIA DE NEMATÓIDES LONGIDORÍDEOS E CHAVE DICOTÔMICA PARA IDENTIFICAÇÃO DE ESPÉCIES DE XIPHINEMA E XIPHIDORUS QUE OCORREM NO BRASIL

ABSTRACT

Ectoparasitic Longidoridae are globally an economically important family of nematodes that cause damage to an extensive range of crop plants by their feeding on plant root cells or transmitting viruses to a wide range of fruit and vegetable crops. Here, we provide an update review of Longidoridae taxonomy, including their basic morphology and the taxonomic characters used to distinguish the seven Longidoridae genera (Australodorus, Longidorus, Longidoroides, Paralongidorus, Paraxiphidorus, Xiphidorus and Xiphinema). In addition, dichotomous keys for the identification of Xiphidorus and Xiphinema species reported in Brazil are presented.

KEY WORDS
Dichotomous key; Longidoridae; Xiphidorus ; Xiphinema ; taxonomy

RESUMO

Nematóides ectoparasitos da família Longidoridae causam danos a grande número de plantas cultivadas no mundo inteiro, alimentando-se diretamente das células das raízes ou transmitindo viroses. A presente revisão aborda a classificação e taxonomia dessa família, incluindo a morfologia básica e as características taxonômicas utilizadas para distinguir os sete gêneros pertencentes a Longidoridae (Australodorus, Longidorus, Longidoroides, Paralongidorus, Paraxiphidorus, Xiphidorus and Xiphinema). Além disso, são apresentadas chaves dicotômicas para facilitar a identificação de espécies de Xiphidorus e Xiphinema que ocorrem no Brasil.

PALAVRAS-CHAVE
Chaves dicotômicas; Longidoridae; Xiphidorus ; Xiphinema ; taxonomia

The Phylum Nematoda is highly diverse in terms of species richness and one of the most abundant metazoan groups on earth (HUGOT et al., 2001). It is estimated that nematodes comprise nearly 90% of all multicellular organisms (Jairajpuri and Ahmad, 1992). Furthermore, LAMBSHEAD (1993) predicted the number of nematode species in marine habitats to be as high as one hundred million, although only 26,646 species have been currently described from all habitats (HUGOT et al., 2001). Nematodes are essentially aquatic organisms, the majority of which are microscopic in size (0.3-3.0 mm), living in a range of habitats, from oceans to the microscopic film of water surrounding soil particles (NORTON, 1978; DE LEY, 2000). Based on their different feeding habits, terrestrial and marine nematodes can be divided into different functional (trophic) groups (YEATES et al., 1993).

Economically, one of the most important functional nematode groups are the plant-parasitic nematodes that live in the soil or inside plant structures such as leaves, stems and mainly roots. Crop losses, in terms of reduced yield and quality, and management practices due to plant-parasitic nematodes were estimated annually at approximately 12% (SASSER & FRECKMAN, 1987), corresponding to monetary losses to world agriculture of approximately US$100 billion. SASSER & FRECKMAN (1987) reported that the ten most economically damaging nematode genera were Meloidogyne, Pratylenchus, Heterodera, Ditylenchus, Globodera, Tylenchulus, Xiphinema, Radopholus, Rotylenchulus and Helicotylenchus. The majority of these plant-parasitic nematodes belong to the order Tylenchida, except Xiphinema (Longidoridae) that is a member of Dorylaimida.

The main focus of this review is the longidorid group of nematodes, especially the genera Xiphinema and Xiphidorus that cause damage to crop plants by their direct feeding on root tips, resulting typically in stunted plant growth with concomitant yield reduction. A few Xiphinema species are also known as vectors of nepoviruses (BROWN et al., 2004) and some of which (X. americanum sensu stricto, X. bricolense, X. californicum and X. rivesi) are quarantine pests (http://www.eppo.org/QUARANTINE/lists.htm).

CLASSIFICATION AND TAXONOMY OF LONGIDORIDAE

Longidoridae is comprised of the following genera: Longidoroides Khan, Chawla & Saha, 1978; Longidorus Micoletzky, 1922; Paralongidorus Siddiqi, Hooper and Khan, 1963; Paraxiphidorus Coomans and Chaves, 1995; Xiphidorus Monteiro, 1976 and Xiphinema Cobb, 1913 (COOMANS, 1996; DOUCET et al., 1998) and their systematics have been debated intensely and reviewed by several authors during the last 30 years (COOMANS, 1985; HUNT, 1993; COOMANS, 1996). Recently, another genus, Australodorus, was described and proposed to be included in Longidoridae (COOMANS et al., 2004).

Classification

Reviewing the systematics of Longidoridae, HUNT (1993) proposed an intermediate classification between the inflationary concept of KHAN et al. (1978) and the more conservative schemes of both LUC & DOUCET (1984) and COOMANS (1985). Later, based on phylogenetic relationships of morphological characters, COOMANS (1996) suggested two possible classifications; the first included a Tribe subdivision and the second scheme was similar to that proposed by HUNT (1993) but updated to include Paraxiphidorus. This study has adopted the classification of Hunt (1993) as follows:

• Order: Dorylaimida Pearse, 1942

• Suborder: Dorylaimina Pearse, 1942

  • superfamily: Dorylaimoidea de Man, 1876 (Thorne, 1934)

    • family: Longidoridae Thorne, 1935 (Meyl, 1961)

      • subfamily: Longidorinae Thorne, 1935

        • genera: Longidorus

        • Longidoroides

        • Paralongidorus

      • subfamily: Xiphidorinae Khan, Chawla & Saha, 1978

        • genera: Paraxiphidorus

        • Xiphidorus

        • Australodorus

      • subfamily: Xiphinematinae Dalmasso, 1969

        • genus: Xiphinema

Taxonomy of Longidoridae

Longidorids are relatively large nematodes (2 to 12 mm in length), with a slender body and have a long, hollow feeding spear (60-250 μm in length) that differentiates Longidoridae from other Dorylaimid groups. The spear is comprised anteriorly by an odontostyle, that punctures the root tip and enables the nematode to feed within root cells whilst remaining exterior to the root, and posteriorly by an odontophore (ARIAS & BRAVO, 1997). The oesophagus consists of a long, narrow anterior tube connecting the spear with a cylindrical bulb that provides the pumping action used to withdraw plant cell contents. (Fig. 1) (BROWN et al., 1995). The bulb contains three large gland cells, one dorsal and two subventral.

Fig. 1
Basic morphology of the anterior region of Xiphidorus and Xiphinema.

Females have various arrangements of possible reproductive systems (Fig. 2): amphidelphic (two genital branches, one running anteriorly and the other posteriorly), monodelphic (one posterior genital branch) or pseudomonodelphic (one posterior functional genital branch whilst the anterior branch is reduced, atrophied and non-functional) (COHN & SHER, 1972; COOMANS et al., 2001). The majority of species have an assumed parthenogenetic mode of reproduction since males are either not known or rare. However, amphimictic reproduction occurs with species where males have been recorded (COOMANS et al., 2001). When present, males have curved spicules with lateral accessory pieces (crura) and ventromedian supplements. Tail morphology is similar in both sexes. Usually there are four juvenile stages, but in a few species there are only three (HALBRENDT & BROWN, 1992; ROBBINS et al., 1996). Juveniles have a similar morphology to that of adults (ARIAS & BRAVO, 1997).

Fig. 2
Arrangements of female reproductive systems in Xiphinema. A, monodelphic; B, pseudomonodelphic; C, amphidelphic. Adapted from COHN & SHER (1972).

The differential taxonomic characteristics of the genera are present in Table 1 and Figure 3, based on that described by LUC & DOUCET (1984), COOMANS & CHAVES (1995), ARIAS & BRAVO (1997) and COOMANS et al. (2004).

Table 1
Taxonomic characters used to distinguish Longidoridae genera (after LUC & DOUCET, 1984; COOMANS & CHAVES, 1995; ARIAS & BRAVO, 1997 and COOMANS et al., 2004).

Code	Taxonomic characters	Longidoridae genera
		Longidorus	Longidoroides	Paralongidorus	Paraxiphidorus	Australodorus	Xiphidorus	Xiphinema
A1	Amphid aperture pore-like or inconspicuous	+	-	-	-	-	-	-
A2	Amphid aperture slit-like	-	+	+	+	+	+	+
B1	Amphids pouch-like	+	+	-	-	-	+	-
B2	Amphids funnel to stirrup shape	-	-	+	+	-	-	+
B3	Amphids bilobed	+	+	+	-	+	-	-
C1	Guide ring located in posterior part of odontostyle	-	-	-	+	+	+	+
C2	Guide ring located in anterior part of odontostyle	+	+	+	-	-	-	-
D1	Odontostyle base plain	+	+	+	-	-	-	-
D2	Odontostyle base forked	-	-	-	+	+	+	+
E1	Odontophore base thickened but not flanged	+	+	+	-	-	-	-
E2	Odontophore base with moderately or weakly developed flanges	-	-	-	+	+	+	-
E3	Odontophore base flanged well developed	-	-	-	-	-	-	+
F1	Dorsal gland nucleus some distance from dorsal gland opening	+	+	+	+	+	+	-
F2	Dorsal gland nucleus close to dorsal gland opening	-	-	-	-	-	-	+

Fig. 3
Taxonomic characters used to distinguish Longidoridae genera. See Table 1 for character codes.

Xiphinema and Xiphidorus taxonomy

Xiphinema and Xiphidorus are the most common longidorid nematodes present in Latin America (see section 4). Identification of Xiphinema and Xiphidorus species is based mostly on female morphology and morphometrics. The most useful taxonomic characters used to separate species are considered to be body length, habitus, shape and size of lip region, shape and size of amphid fovea, spear (odontostyle and/or odontophore length), length and shape of tail, vulva position, characteristics of the female genital tract and uterine differentiation (ARIAS & BRAVO, 1997; BROWN, 1997).

Xiphinema

Xiphinema is the most widely distributed and the largest genus, in terms of speciation, of the Longidoridae (COOMANS et al., 2001). Xiphinema is currently comprised of 258 valid taxa, including 196 non X. americanum-group species listed by COOMANS et al. (2001), 49 X. americanum-group species (LAMBERTI et al., 2004) and the following 13 recently described new species: X. waimungui (YEATES et al., 1997); X. enigmatum, X. torvum, X. variegatum, X. vicarium (SIDDIQI, 2000a); X. bambusi and X. bhutanense (GANGULY et al., 2000); X. mali (GANGULY et al., 2002); X. zyzy (HEYNS & SWART, 2002); X. naturale (LAMBERTI et al., 2002b); X. udaipurensis and X. kesarii (SIDDIQUI & PARIHAR, 2002); X. parasimile (BARSI & LAMBERTI, 2004).

As with all longidorids, Xiphinema are polyphagous, migratory ectoparasites and survive in soil for three to five years (TAYLOR & BROWN, 1997).

Xiphinema species have a characteristic flanged odontophore, forked junction of the odontostyle and odontophore, posteriorly located spear guiding apparatus near the odontostyle base, amphid funnel to stirrup shape with aperture slit-like and dorsal gland nucleus close to dorsal gland opening (Fig. 1) (Table 1) (LUC & DOUCET, 1984).

A polytomous key was erected for the identification of Xiphinema based on their comparatively large morphological diversity and relative ease of distinguishing morphological and morphometric characteristics for the majority of species (LOOF & LUC, 1990, 1993; LOOF et al., 1996). However, species comprising the X. americanum-group were excluded from this polytomous key as several species of this group are only distinguished by minor morphometric or morphological differences (LOOF & LUC, 1990; BROWN & HALBRENDT, 1997). Regional polytomous keys were published (LAMBERTI et al., 2000) as a practical means for identifying the 51 (now 50 species after taxonomic revision by LAMBERTI et al., 2004 and description of X. parasimile by BARSI & LAMBERTI, 2004) putative species composing of the X. americanum group, although reservations about the reliability of the codes used in this key have subsequently been presented (LUC & BAUJARD, 2001). Recently, revised polytomous and dichotomous keys for the identification of 49 (two are now species inquirendae) X. americanum-group species were published (LAMBERTI et al., 2004), based on primary quantitative taxonomic characters, namely: odontostyle and tail length, and the ratios c’ (tail length/body width at anus), V (distance from head end to vulva/body length) (SIDDIQI, 2000b), a (body length/maximum body length) and c (body length/ tail length) proposed by de MAN (1884).

Xiphidorus

The Longidoridae genus, Xiphidorus, comprises nematodes with the following taxonomic characteristics: flanged odontophore, a forked junction of the odontostyle and odontophore, posteriorly located spear guiding apparatus near the odontostyle base, amphid pouch shape with an aperture as a small transverse slit, dorsal gland nucleus some distance from dorsal gland opening and the subventral gland nuclei more developed than the dorsal gland nucleus (Fig. 1). Xiphidorus combines taxonomic characteristics of other longidorids. The spear and spear-guide ring are similar to those of Australodorus, Xiphinema and Paraxiphidorus, but amphid shape and oesophageal gland patterns are closer to those of Longidorus and Longidoroides (Figs. 1 and 3) (Table 1) (MONTEIRO, 1976; LUC & DOUCET, 1984).

Nematodes of this genus are indigenous to Latin America (COOMANS, 1985; DOUCET et al., 1998) and thus have a more restricted geographical distribution than the closely related Xiphinema (COOMANS et al., 2001).

ECONOMIC IMPORTANCE OF LONGIDORIDS

As noted in section 1, longidorid nematodes cause damage to an extensive range of crop plants by their direct feeding on plant root cells. However, a few species are also capable of transmitting viruses, leading to diseases in a wide range of fruit and vegetable crops (BROWN et al., 1995; BROWN et al., 2004; TAYLOR & BROWN, 1997) and are of potentially greater economic importance.

The economic importance of Xiphidorus with respect to crop damage is unknown. However, histopathological studies under controlled conditions indicated that X. minor fed on the root tips of rice and tomato (LEONE et al., 1999) resulting in swollen tips, typical of damage by longidorid nematodes (TAYLOR & BROWN, 1997).

Virus transmission

The natural transmission of a nepovirus by Longidoridae was first demonstrated by HEWITT et al. (1958) who reported X. index as the natural vector of grapevine fanleaf virus in vineyards in California. Currently, eight Longidorus, one Paralongidorus and ten Xiphinema species are vectors of 12 viruses belonging to the genus Nepovirus (Table 2) (BROWN et al., 2004).

Table 2
Virus vector nematode species from the family Longidoridae and their associated nepoviruses (adapted from BROWN et al., 2004).

Vector Species		Virus
Longidorus apulus		artichoke Italian latent
L. arthensis		cherry rosette disease
L. attenuatus		tomato black ring
L. diadecturus		peach rosette mosaic
L. elongatus		raspberry ringspot
		tomato black ring
L. fasciatus		artichoke Italian latent
L. martini		mulberry ringspot
L. macrosoma		raspberry ringspot
Paralongidorus maximus		raspberry ringspot
Xiphinema americanum		cherry rosette disease
	sensu lato	peach rosette mosaic
		tobacco ringspot
		tomato black ring
X. americanum sensu stricto		cherry rosette disease
		tobacco ringspot
		tomato black ring
X. bricolensis		tomato black ring
X. californicum		cherry rosette disease
		tobacco ringspot
		tomato black ring
X. diversicaudatum		arabis mosaic
		strawberry latent ringspot
X. index		grapevine fanleaf
X. intermedium		tobacco ringspot
		tomato black ring
X. italiae		grapevine fanleaf
X. rivesi		cherry rosette disease
		tobacco ringspot
		tomato black ring
X. tarjanense		tobacco ringspot
		tomato black ring

Most of the previous research on longidorids has occurred in North America and Europe, with few investigations having been done in Latin America, Asia, or Africa. In North America, four viruses (cherry rosette disease, peach rosette mosaic, tobacco ringspot and tomato black ring) transmitted by species belonging to the X. americanum-group cause damage to a wide range of fruit and vegetable crops (TAYLOR & BROWN, 1997).

Direct damage

Despite the many studies on the taxonomy, systematics and the geographical distribution of longidorid nematodes, there is a paucity of experimental data concerning the direct damage (cf. indirect damage due to virus transmission) caused by indivi dual species on particular hosts (TAYLOR & BROWN, 1997). However, the pathogenicity of Xiphinema species has been demonstrated for a few host plants. For example, X. longicaudatum severely depressed the growth of eggplant (Solanum melongena) in Africa (Fig. 4) in a "screen house" (LAMBERTI et al., 1992). Plants infected with this nematode were stunted and had a reduced root system. Also, X. ifacolum suppressed the plant growth of okra, pepper, rice and tomato (LAMBERTI et al., 1987a; LAMBERTI et al., 1992).

Fig. 4
Root systems and growth of eggplant infected with Xiphinema longicaudatum (left and centre) compared with control plants (right). Adapted from LAMBERTI et al. (1992).

DI VITO et al. (1985) investigated the relationship between population density of X. index and the growth of grapevine cv. Aglianico. In that study, a population density of 80 X. index 10 cm^-3 soil resulted in stunted plants with only one or two reddish true leaves and the presence of relatively large root galls. Also, in microplots, X. americanum reduced fruit yields of grapevine cultivars Vidal and Vignoles in Michigan, USA (RAMSDELL et al., 1996).

Xiphinema species feed on the root tips or other parts of young, actively growing roots (TAYLOR & BROWN, 1997). For example, X. diversicaudatum feeds at the root tips, causing prominent and subterminal swellings in roots of rose, strawberry, celery, several crop plants and weeds (TAYLOR & BROWN, 1997 and references therein). Also, X. bakeri feeding at the root tips of Pseudotsuga menziesii seedlings caused darkening, swelling and cessation of root growth (SUTHERLAND & DUNN, 1970). However, Xiphinema spp. are not exclusively root tip feeders as X. brevicolle and X. index were observed to feed along the seedling roots of Bidens tripartite, Urtica urens and Vitis vinifera causing darkening of roots and cortex breakdown (COHN, 1970).

The family Longidoridae in Latin America

Of the seven Longidoridae genera, only species belonging to Australodorus, Longidoroides, Longidorus, Paraxiphidorus, Xiphidorus and Xiphinema have been reported from Latin America (DOUCET et al., 1998, COOMANS et al., 2004). From the 53 valid longidorid species reported by DOUCET et al. (1998), 42 were Xiphinema, 22 of which, (X. basiri, X. brasiliense, X. brevicolle, X. californicum (virus-vector species), X. clavicaudatum, X. costaricense, X. dimidiatum, X. elongatum, X. ensuculiferum, X. fluminense, X. georgianum, X. guillaumeti, X. ifacolum, X. index (virus-vector species), X. krugi, X. machoni, X. pachtaicum, X. parasetariae, X. paritaliae, X. paulistanum, X. setariae/X. vulgare complex and X. surinamense), occur in Brazil. Recently, another seven species of Xiphinema were reported from Brazil: X. torvum, X. variegatum and X. vicarium (SIDDIQI, 2000a) and X. diffusum, X. longicaudatum, X. oxycaudatum and X. peruvianum (OLIVEIRA et al., 2003).

Currently, there are eight valid Xiphidorus species (X. achalae, X. amazonensis, X. balcarceanus, X. minor, X. parthenus, X. saladillensis, X. uruguayensis and X. yepesara) that have been recorded from the following South American countries: Argentina, Brazil, Uruguay and Venezuela (MONTEIRO, 1976; MONTEIRO et al., 1981; CHAVES & COOMANS, 1984; LUC & DOUCET, 1984; UESUGI et al., 1985; RASHID et al., 1986; COOMANS et al., 1996; DECRAEMER et al., 1996, 1998; DOUCET et al., 1998; CHAVES et al., 1999; LAMBERTI et al., 1999) and two undescribed species from Argentina and Bolivia (HUNT, 1993; DECRAEMER et al., 1996). In Brazil, X. amazonensis, X. balcarceanus, X. minor, X. parthenus and X. yepesara have previously been recorded (DOUCET et al., 1998; OLIVEIRA et al., 2003).

The taxonomy of X. parthenus sensu MONTEIRO et al. (1981) and X. yepesara sensu MONTEIRO (1976) is controversial. DECRAEMER et al. (1996) queried the classification and suggested the replacement of both species with two sub-species, namely X. yepesara parthenus and X. yepesara yepesara. Subsequently, CHAVES et al. (1999) rejected DECRAEMER et al. (1996) and suggested synonymization of both species to X. yepesara. However, recently, morphometric and molecular data suggested that X. parthenus and X. yepesara are distinct taxonomic species contrary to their previous subspecies status and synonymization. Thus the retention of the original species proposed by MONTEIRO (1976) and MONTEIRO et al. (1981) is recommended (OLIVEIRA et al., 2004).

KEY TO IDENTIFICATION OF XIPHINEMA SPECIES RECORDED IN BRAZIL.

A dichotomous key was prepared based on the appropriate morphological and morphometric characteristics of female Xiphinema species recorded in Brazil (OLIVEIRA et al., 2003). The characters used were according to LOOF & LUC (1990), LAMBERTI et al. (2000) and COOMANS et al. (2001).

• 1. Female anterior genital branch completely lacking or incomplete…………..............................................2 (Fig. 2AB)

  Female with two complete genital branches………………………………..........................................................12 (Fig. 2C)

• 2. Anterior genital branch completely lacking, uterus absent….............................................……………..….3 (Fig. 2A)

  Anterior genital branch without ovary; uterus present, oviduct reduced….............................................…4 (Fig. 2B)

• 3. Tail hemispherical with a terminal peg…………..................................................…………...…X. brasiliense (Fig. 5B)

  Tail regularly hemispherical without peg ……………......................................................……..X. ensiculiferum (Fig. 5F)

• 4. Tail long, attenuated………….........................................................…………………..………………….....……….5 (Fig. 5H)

  Tail short from conical to hemispherical………………..………….................................................................………………….6

• 5. Ratio c’ > 5.0……………...................................................................………………………….….X. longicaudatum (Fig. 5H)

  Ratio c’ < 5 .0……………………………………………………..........................................................................…X. clavicaudatum

• 6. Tail conical-conoid……………...............................................................….…………………………………..……..7 (Fig. 6B)

  Tail regularly hemispherical……………….…………………………...................................................................…...8 (Fig. 7F)

• 7. Tail with a terminal peg………………………..............................................................…………………………X. dimidiatum

  Tail with rounded to subdigitate bulged terminus ……….....................................................……….X. krugi (Fig. 6B-D)

• 8. Lip region offset from body………………..……..................................................................………………………………….....9

  Lip region continuous with body………………………………………..………….................................................................10

• 9. Body length < 3.0 mm….……....................................................................…………………………………..…....X. costaricense

  Body length > 3.0 mm……………………………………………..…….........................................................................…X. torvum

• 10. Body length ca. 2.0 – 2.3 mm…………….................……......................................…….…..…...X. variegatum (Fig. 7GH)

  Body length ca. 2.5 – 2.7 mm ...…………………………………………………….........................................................................11

• 11. Ratio c > 100……………………............................................................………………..…………………….…..X. vicarium

  Ratio c < 100………………………………….....................................................................…….……….X. surinamense (Fig. 7EF)

• 12. Presence of a well-developed Z organ…………………….......................................................... ..………………………13

  No Z organ; with or without other uterine differentiation……………….…………..............................................................14

• 13. Ratio c' > 1.3 ……….................................................................................................................................X. ifacolum (Fig. 6F)

• 14. Ratio c' < 1.3.……………………………………….......................................................................................................X. machoni.

• 15. Tail shape hemispherical or conoid with broadly rouded terminus..............................................................................15

  Tail conical more or less elongate…..................................................................................................................................….……..17

• 15. Presence of a terminal peg………….............................................................………….………………………………X. index

  Broadly rounded terminus without peg…………………………………...............................................................………...….16

• 16. V 52 – 53%…………….................................................................…………………….……………………...……X guillaumeti

  V 47 – 48%………………………………………………………….................................................................................X. fluminense

• 17. Tail conical subdigitate………………..........................................................………………………...…………..18 (Fig. 7D)

  Tail conical short or elongate………………………...…..........................................................…..…… 19 (Figs. 8B and 5D)

• 18. V > 48%………...................................................................…………………….………………………………………...X. basiri.

  V d ≤ 48% …….……………..…..........................................................................................................................X. setariae/X. vulgare

• 19. Tail conical elongate, c’ > 2.0.…………........................................................……………………………….....20 (Fig. 5D)

  Tail conical short, c’ d□ ≤ 2.0..…..………………………………...............................................................…….…..21 (Fig. 8B)

• 20. Odontostyle length < 100 µm ……….………........................................................……….…...….X. elongatum (Fig. 5C)

  Odontostyle length > 100 µm ……...............................................................……X. parasetariae and X. paritaliae (Fig. 7A)

  (the two species are indistinguishable morphometrically, X. parasetariae is placed among species inquirendae by LOOF & LUC, 1990).

• V < 45%………..………….................................................................…………………………………………....X. paulistanum

  V > 45%……………………………………………………..…………............................................................................…………...22

• 22. Value of c’ d≤ 1.1………………................................................................…………………………..…………………...…….23

  Value of c’ > 1.1 …………………….…………………..………………….........................................................................….…….24

• 23. Odontostyle length ca. 100 µm ………….....................................................…..……………….….X. brevicolle (Fig. 8A)

  Odontostyle length ca. 90 µm ..…………………………...........................................................………..X. diffusum (Fig. 8C)

• 24. Odontostyle length ca. 80 µm ………....................................................………….…………....X. oxycaudatum (Fig. 8E)

  Odontostyle length > 80 µm………..……………………………...……….....................................................................……...…25

• V > 55% …………....................................................................……………………………...……………………...X. pachtaicum

  V < 55% …….………………………….………………………..........................................................................…………………....26

• 26. Odontostyle length e ≥ 100 µm……..........................................................…………………….………………X. georgianum.

  Odontostyle length < 100 µm…………....................................................................….…………………..………………………27

• Ratio c’ e ≥ 1.5……................................................................………………………………………...…………..X. californicum.

  Ratio c’ < 1.5……...……………………….................……..................................................................….X. peruvianum (Fig. 8H)

KEY TO IDENTIFICATION OF XIPHIDORUS SPECIES

Previously, two Xiphidorus keys were published (DECRAEMER et al., 1996; ARIAS & BRAVO, 1997).

However, neither key included X. uruguayensis. Also, ARIAS & BRAVO (1997) considered X. tucumanensis as a valid species instead of a synonym of X. balcarceanus as proposed by DECRAEMER et al. (1996). Thus, the following updated dichotomous key was prepared based on relevant morphological and morphometric characteristics of females of the eight putative Xiphidorus species.

Dichotomous key for the identification of Xiphidorus species.

• 1 - Body length d≤ 2.5 mm………….……….....…………..2

  Body length > 2.5 mm………….……………………..…..3

• 2 - Tail length < 30.0 µm ….……...........X. minor (Fig. 9F)

  Tail length > 30.0 µm .……..........….…….....X. saladillensis

• 3 - Body length > 4.5 mm………..….............……………..4

  Body length < 4.5 mm………….......…...…………………..6

• 4 - Presence of prominent uterine.....X. achalae (Fig. 10A) spines

  Uterine spines inconspicuous or absent.....………..…...5

• 5 - Odontostyle length > 110…………..X. uruguayensis

  µm, body length > 6.5 mm

  Odontostyle length < 110 µm, body….......X. amazonensis

  length d ≤ 6.5 mm

• 6 - Amphidial............X. balcarceanus (Figs. 9AB and 10B)

  pouch narrow, < 50% of the corresponding body width

  Amphidial pouch wide, >....................…….....7 (Fig. 10C)

  50% of the corresponding body width

• 7 - Number of ...........…....X. parthenus (Figs. 9F and 10D)

  lateral pores < 100, tail conical-rounded

  Number of lateral.......X. yepesara (Figs. 9H and 10E-G)

  pores ca. 200, tail conoid

Fig. 5
Photomicrographs of female anterior and posterior regions of: A-B, Xiphinema brasiliense; C-D, X. elongatum; E-F, X. ensiculiferum; G-H, X. longicaudatum.

Fig. 6
Photomicrographs of female anterior and posterior regions of: A-B, Xiphinema krugi (tail subdigitate); C-D, X. krugi (tail digitate); E-F, X. ifacolum (tail ventrally arcuate with typical blind canal, indicated by an arrow); G-H, X. ifacolum (tail conoid without blind canal).

Fig. 7
Photomicrographs of female anterior and posterior regions of: A-B, Xiphinema paritaliae; C-D, X. setariae/vulgare; E-F, X. surinamense; G-H, X. variegatum.

Fig. 8
Photomicrographs of female anterior and posterior regions of Xiphinema americanum-group species. A-B, X. brevicolle; C-D, X. diffusum; E-F, X. oxycaudatum; G-H, X. peruvianum.

Fig. 9
Photomicrographs of female anterior and posterior regions of: A-B, Xiphidorus balcarceanus; C-D, X. minor; E-F, X. parthenus; G-H, X. yepesara.

Fig. 10
A, uterine spines in Xiphidorus achalae; B, amphidial pouch narrow in X. balcarceanus; C, amphidial pouch wide in X. yepesara; D, tail conical-rounded in X. parthenus; E-G, tail conoid in X. yepesara. Adapted from MONTEIRO (1976), MONTEIRO et al. (1981), CHAVES & COOMANS (1984), LUC & DOUCET (1984), DECRAEMER et al. (1996).

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Publication Dates

• Publication in this collection
  10 Jan 2022
• Date of issue
  Jan-Mar 2006

History

• Received
  31 Dec 2005
• Accepted
  09 Feb 2006