Les structures cuticulaires de #Radopholus similis$ provenant de Côte d'Ivoire et de Guinée Bissau ont été étudiées en microscopie électronique à balayage. Les résultats montrent que les structures cuticulaires sont identiques dans les deux populations et exhibent une variabilité supérieure à celle observée dans les populations américaines de #R. similis$ et de #R. citrophilus$ qui est proposé comme un synonyme mineur de #R. similis$. Des données additionnelles sont apportées sur la forme de la queue et les champs latéraux chez la femelle, et sur la forme de la région céphalique et de la bursa chez le mâle. (Résumé d'auteur

Baujard, Pierre

Mounport, D.

Nicole, Michel

Sarah, J.L.

Valette, C.

Horizon / Pleins textes

Fundam. appl. Nemarol., 1998, 21 (2), 139-146
Scanning electron microscope study
of two Mrican populations of Radopholus similis
(Nematoda: Pratylenchidae) and proposai of
R. citrophilus as a junior sYfionym of R. similis
Catherine VALETTE*, Danamou MOUNPORT**, Michel NlCOLE***,jean-Louis SARAH*
and Pierre BAUJARD****
*Laboratoire de Némalologie, CIRAD-FLHOR, B.P. 5035, 34032 MontfJellier cedex 1, Frame,
**Département de Biologie Animale, Faculté des Sciences, Univ!?'rsitéCheikh Anta Diop, Dakar, Sénégal,
*'k'i'Laboratoire de Phytopathologie, ORSTOlvI, B.P. 5045, 34032 Montpelli!?'r cedex, France,
and *'k'k'k Muséum National d' Histoire Naturelle, Laboratoirf de Biologie Parasitaire, Protistologie,
/-Ielmint/wlogie, 61 rue Buffon, 75005 Paris, France.
Acceptecl for publication 22 May 1997.
Swnmary - Cuticular structures of IWO African populations of Radopholus similis from the Ivory Coast and Guinea Bissau were
observed under the scanning electron microscope. These two populations have similar cuticular structures, which exhibited a
range of variation over1apping that described in American population of R. simziis and R. cilmphilus. Consequently, R. cilrophilus
is proposed as a junior synonym of R. similis. Additional data are provided on female tail shape and laterai fields and male head
and bursa shape. © Elsevier - ORSTOM
Résumé - Étude en m.icroscopie électronique à balayage de deux populations africaines de Radopholus similis
(Nen7.atoda: Pratylenchidae) et proposition de R. citrophilus com.m.e synonYn1.e m.ineur de R. similis - Les struc-
tures cuticulaires de Radopholus similis provenant de Côte d'Ivoire et de Guinée Bissau ont été étudiées en microscopie électro-
nique à balayage. Les résultats montrent que les structures cuticulaires sont identiques dans les deux populations et exhibent
une variabilité supérieure à celle observée dans les populations américaines de R. similis et de R. cùrophilus qui est proposé
comme un synonyme mineur de R. similis. Des données additionnelles sont apportées sur la forme de la queue et les champs
latéraux chez la femelle, et sur la forme de la région céphalique et de la bursa chez le màle. rC Elsevier - ORSTOM
Keywords: curicular structures, Radopholus citrophilus, R. similis, scanning electron microscopy, taxonomy, variability.
Two races have long been recognized (Ducharme &
Birchfield, 1956) in Radopholus similis (Cobb, 1893)
Thome, 1949; one race parasitizes banana but not cit-
rus, the other parasitizes both citrus and banana.
Other differences were described between the two
races, i.e., karyotype with n=4 in the banana race vs.
n=5 in the citrus race (Huenel & Dickson, 1981;
Huetrel et al., 1984), differences in isoenzymes and
proteins (Huetrel et al., 1983a, b), and differences in
sexual behaviour (Huetrel et al., 1982).
Latter, Huetrel et al. (1984) proposed the citrus
race as a new species, R. cùrophilus Huetrel, Dickson
& Kaplan, 1984, emphasizing the fact that it was the
first sibling species described in plant parasitic nema-
todes and that it was not morpho-anatomically dis tin-
guishable from R. similis. Consequently, the diagnosis
only referred to karyotypes, enzymes and proteins,
and sexual behaviour. Recently Hahn et al. (1996)
demonstrated that the chromosome number cannot
be used as a diagnostic feature in R. similis.
Absence of morpho-anatomical differences between
the two species led sorne taxonomists to consider
R. cùrophilus as a subspecies within R. similis (see
Siddiqi, 1986).
Fundam. appl. Nemarol. 1164-5571/98/02/© Elsevier - OR5TOM
Huetrel and Yaegashi (1988) examined specimens
of the two taxa with scanning electron microscopy
(SEM) and claimed that they can be differentiated at
the species level by using minute external characters,
clearly visible only under SEM. These characters were
the shape of oral disc and laterallip sectors in females,
the number of body annules at level of the vulva, and
the number of "genital papillae" on the anterior cloa-
cal lip in male.
The examination of specimens from two African
populations of R. similis show that the differentiating
power of these SEM characters are not as strong as
claimed by Huetrel and Yaegashi (1988).
Materials and rnethods
Two populations of R. similis were studied under
SEM: 1) one population collected in 1990 at Bula,
Guinee-Bissau (= GB pop.) and reared on cowpea
(Vigna unguiculata [L.D Walp.) in the laboratory at
Dakar (Senegal), and il) one population collected at
Anguédédou, Ivory Coast (= IC pop.) and reared in
the laboratory on carrot disks culture (Fallas et al.,
1995).
139
C. Va/elle et al.
Fig. 1. Fema/e head morphology of Radopholus similis, Guinea Bissau popu/alion (A, E; B, F; C, G; D, H: La/era/ and face views
of [he sarne specimen, respeclively; scale bars = J pm).
Nematodes extracted from sail and roots (GB pop.)
or from carrot disks (lC pop.) were prepared for
SEM as described by Baujard and Pariselle (1987).
Thirty females and males of each population were
observed.
140
Results
HEAO MORPHOLOGY
Females: Shape of the labial disc variable in the GB
pop., depending on the degree of dorsal and ventral
Fundam. appL Nemawl.
SElvI slUdy of Radopholus similis
~t
Fig. 2. Male head morphology of Radopholus similis, Guinea Bissau populacion (A, D; B, E; C, F: Face and lacerai views of che same
specimen, respeccive/y; scale bars == 1 pm).
fusion of the labial disc with the first head annule; in
the IC pop., labial disc rounded to elongate (Fig. 1).
In both populations, the lateral lips extend over the
whole cephalic region in 50 % of the females, and stop
just before the last head annule in the other specimens.
Number ofhead annules variable in the GB pop.: two
(13 % of the specimens), three (27 %), four (27 %), or
five (7 %); in 27 % of the specimens, one or two head
annules are partly subdivided, which means that the
number of head annules is different on each side of the
head: two-five, three-four, or three-five. In the IC
pop., three head annules are always present.
Males: Head quadrilobed in face view (Fig. 2), with
four deep dorso-ventral and lateral grooves; laterally,
Vol. 21, n° 2 - 1998
these grooves panially covered by the lateral lip sec-
tors extending longitudinally over the whole head;
first head annule with a small, more or less rounded,
not weil marked labial disc; submedian lip sectors
appearing totally fused together; head with two to four
head annules.
VULVA AREA
Vulva, a transverse slit of medium length (30-40 %
of the corresponding body diameter); vulval lips pro-
truding or not; at the level of the vulva, transverse
body annulation completely inrerrupted by vulva
opening (=annules terminating at vulva in Huetrel
and Yaegashi, 1988) over two (15 %), three (71 %), or
141
C. Valelle et al.
Fig. 3. Female vulval region and laierai fields of Radopholus similis, Ivory Coase (left column) and Guinea Bissau (righe column)
populations (E, F: Lacerai and subvemral views of che same specimen, respectively; scale bars = JO pm).
142 Fundam. appl. Nemawl.
SEM swdy of Radopholus similis
Fig. 4. Male (A-E) andfemale (F-G) cail of Radopholus similis, Guinea Bissau popularion (Scale bars = /0 pm).
Vol. 21, nO 2 - 1998 143
C. Va/elle et al.
Fig. 5. Cloaca/ region ojRactopholus similis, Gwnea Bissau population (Sc ale bars = 1 fJ-m).
four (15 %) body am'.ules in the l C pop (Fig. 3, A-C)
and one (15 %), rwo (28 %), or three (57 %) body
annules in the GB pop. (Fig. 3, D-H).
FEMALE LATERAL FIELDS
Lateral fields occupying 27-53 % of the correspond-
ing body diameter, with four incisures delimiting
three bands of equal size, more or less regularly areo-
lated (Fig. 3, A, B, D, E, H).
144
TAIL SHAPE
Female: Tail appearing most often regularly conoid,
rarely subcylindrical; distal part of the tail variable in
shape in both populations: truncate, rounded, or
bearing a short (3-4 /lm) and weil marked mucro
(Fig. 4, F-G).
Male: Tail generally regularly conoid, rarely subcy-
lindrical; tail ending mostly in a short mucro as
Fundam. app/. NemalOL
SEM study of Radopholus similis
Table 1. Variabilùy of charaere rs used for lhe differentialion of Radopholus similis and R. citrophilus.
GeIÙtal papillae
Annules interrupted by vulva
Labial disc
Lat. lip sectors
R. similis
Huetrel & Yaegashi (1988)
0-2
2
± hexagonal
reaching base
of 3rd lip annule
Present study
0-6
1-5
rounded/oval
reaching penultimate
lip annule (2-5)
R. cùraphilus
Huettel & Yaegashi (1988)
3-7
3
± rounded
not reaching base
of 3rd annule
described for female, rarely in an abrupt truncate ter-
minus (Fig. 4, A-E). Bursa adanal, occupying 33-
63 % of me tail lengm. In bom populations, 50 % of
me specimens have anterior cloacal lip devoid of any
ornamentation; in the omer specimens, one to six
appendices present, variable in lengm (from a short
tubercle to a thin appendice, 0.6 Ilm long) and
appearing as simple outgrowms of me cloacal lip and
not as papillae since no pore Or omer type of aperture
can be observed (Fig. 5).
Discussion
In the two Afriqn populations of R. similis studied,
variations are observed in the cUticular structures
greater than previously described (Orton Williams &
Siddiqi, 1973): females wim two-five vs. mree-four
head annules, lateral fields regularly areolated vs.
areolated only tawards extremities, tail terminus
rounded ta truncate, with or without terminal muera
vs. rounded or indented wimoUt any terminal mucro;
males with two-four vs. mree-five head annules, bursa
extending over 33-63 vs. about 66 % of me tail.
The male head, observed for the first time under
SEM, exhibited a four-lobed shape, very close ta mat
observed in the genus Belonolaimus in the family
Belonolaimidae; this shape, unusual in the suborder
Tylenchina, has never been observed in the family
Pratylenchidae or in omer families with endoparasitic
forms; Baldwin and Cap (1992) observed mat "the
submedial lips are separated by deep indentations" in
males of Radopholus spp. and considered this pattern
close ta mat of Nacobbus males, almough SEM obser-
vations by Doucet (1989) revealed a "classical" head
pattern wimout any longitudinal indentations in
N aberrans.
In the two populations studied, me SEM characters
considered as diagnostic by Huetrel and Yaegashi
(1988) ail showed variation overlapping the differ-
ences between R. similis and R. cùrophilus described by
mese aumors (Table 1).
The present observations show mat me two species
cannot be differentiated morphologically, even with
me use of SEM.
Vol. 21, nO 2 - 1998
Also karyotypes do not appear a safe way for such a
differentiation (see above). Finally differences reCOr-
ded in enzyme and protein patterns cannot be assu-
med to be characteristic at species or at race level.
Moreover, it has been demonstrated mat R. similis can
reproduce by parthenogenesis (Brooks & Perry, 1962),
a fact that lessens the importance of the sexual attrac-
tion.
Therefore it appears more reasonable to consider
R. cùrophilus Huettel, Dickson & Kaplan, 1984 as a
junior synonym of R. similis (Cobb, 1893) Thorne,
1949, me citrus and banana races representing differ-
entiated pathotypes.
Acknowledgernents
The authors thank Dr M. Luc for his valuable comments
and suggestions on the manuscript.
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Fundam. appl. Nemawl.


Scanning electron microscope study of two African populations of Radopholus similis (Nematoda : Pratylenchidae) and proposal of R. citrophilus as a junior synonym of R. similis

Scanning electron microscope study of two African populations of Radopholus similis (Nematoda : Pratylenchidae) and proposal of R. citrophilus as a junior synonym of R. similis

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