Identification of Meloidogyne : a general assessment
and
a comparison of male morphology Üsing light rnicroscopy,
with
a key to 24 species
Susan B. JEPSON
Rothamsted Experimental Station, Harpenden, Herts., England.
SUMMARY
Quantitative characters utilised in the identification of Meloidogyne species are assessed for stability in terms
of their coefficient of variation and interspecific overlap. Only eleven male, seven female and eleven second-stage
juvenile characters aid species differentiation. Males of
24 species are differentiated in a key primarily based on
qualitative morphology of the head and stylet observed in the light microscope. Twenty one species can be readily
identified using only head and stylet shape, stylet length and \
distance of dorsal oesophageal gland orifice €rom stylet
base.
M. incognita incognita, M. incognita wartellei and M. grahami cannot be separated using male characters
alone. In females, qualitative characters to be considered are stylet and perinealpattern morphology, and, in second-
stage juveniles, tail shape. Qualitative characters should be used in preference to measurements for species identi-
fication, although combinations of these may serve to group species, particularly when the coefficient of variation
RÉSUMÉ
Identification des Meloidogyne : considération ge’ne’rale et comparaison de la morphologie des mâles
en microscopie optique, avec une clé de 24 espèces
La stabilité des caractères quantitatifs utilisés pour l\
’identification des espèces de Meloidogyne est évaluée en
se basant sur leur coefficient de variation et leur chevauchement interspécifique. Onze caractères des mâles, sept
des femelles et onze des juvéniles de second stade sont utilisés dans la différenciation des espèces. Les mâles de
24 espèces sont différenciés dans une clé fondée, en premier lieu, sur des caractères qualitatifs concernant la mor-
phologie de la tête et du stylet observés en microscopie optique. Vingt et une espèces peuvent être différenciées en
n’utilisant que la forme
de la tête et du stylet, la longueur du stylet et la distance entre le débouché de la glande
cesophagienne dorsale et la base du stylet. M. incognita incognita, M. incognita wartellei et M. grahami ne peuvent
être distinguées en n’utilisant que les caractères des mâles. Chez les femelles, les caractères qualitatifs à considérer
concernent la morphologie du stylet et de la zone périnéale et, chez les juvéniles du deuxième stade, la forme de la queue. Dans l’identification des espèces, les caractères qualitatifs doivent être utilisés de pré\
férence aux mensu-
rations, bien que des combinaisons de ces dernières puissent servir à grouper des espèces, particulièrement si le
coefficient de variation est
chements interspécifiques limit6s.
(l) Work supported by a United Iiingdom Overseas Development Administration Research Grant\
, No R3566.
Revue Nèmatol. 6 (2) : 291-309 (1983) 29 1
S. B. Jepson
Identification of Meloidogyne species has been
based on the female perineal pattern, although often
this has been supplemented by up to 140 other characters from the different life stages (see major
references
: Whitehead, 1968 ; Esser, Perry & Taylor,
1976
; Franklin, 1978 ; Taylor & Sasser, 1978). The
perineal pattern is variable in most species, but
especially
so in the evolutionarily advanced species,
such
as M. incognita, which have broad host ranges
and reproduce entirely by parthenogenesis (Trianta-
phyllou, 1979).
A number of species have perineal
patterns
of a similar type ’ (e.g. M. incognita and
related species) and nlay be grouped on this basis,
while others are unique. Many early descriptions are
inadequate with poor illustrations and place much
emphasis on measurements of specimens from single
populations. Comparisons of different populations
are essential to assess intraspecific variation and to
adequately characterise
a new species. Only those
characters which exhibit least variation in the genus
as a whole should be used.
The use of morphological characters of male heads
of
Meloidogyne species for their identification has
been highlighted
by Eisenback and Hirschmann
(1980) and Eisenback
et .al. (1981). In a scanning
electron microscope (SEM) study it was shown that
races
A and B of M. hapla and their cytological forms,
M. arenaria, M. incoqnita and M. javanica, showed
differences in labial and cephalic sensilla, shape and
proportion of labial disc and lips, and markings on
the head region. A similar study of the same species
included
a comparison of scanning and light micro-
graphs of the male and female stylet and showed
these four species to be morphologically distinct
(Eisenback, Hirschmann
& Triantaphyllou, 1980 ;
Eisenback et al., 1981).
The characters currently used for differentiating
Meloidogyne species are assessed. Qualitative char-
acters are shown to be more useful than measurements
and their value is illustrated using males of 24 species,
which are differentiated in
a key.
Materials and methods
CHARACTER ASSESSMENT
Thirty Meloidogyne species were observed ; four-
teen (21 populations) were in culture at Rothamsted,
and others in the Rothamst,ed and USDA slide
collections. Mean, range, coefkient
of variation and
degree of overlap between species for each character
were determined
; published data were also c,onsider-
292 ed. Quantitative and qualitative characters studied
are listed
below”
:
Males : a, b, b’, cl c’, O, Tl d, m, max. body width,
body length, head shape, head height, head width,
head height/head width, number
of post labial
annules, stylet length, stylet cone length, style1 shape,
stylet knob width, stylet knob length, distance dorsal
oesophageal gland orifice (DGO) from stylet base,
stylet knob
+ stylet shaft length, length median bulb,
width median bulb, distance anterior end
to base
median bulb, position of hemizonid relative to
excretory pore, distance excretory pore to base
median bulb, distance anterior end to excretory pore, distance anterior end to centre median bulb, length
median bulb “valves”, width median bulb “valves” distance anterior end to hemizonid, lenglh oesopha-
gus, number of lateral field incisures, width lateral
field, areolation of lateral field, length testis, tail
width at anus, length/width tail, distance anterior end of testis to tail terminus, distance phasmids to
tail terminus, annule width, spicule length, guber- naculum length.
Secorzd-stage juveniles : a, b, b‘, b”, c, cf, O, d, m,
max. body width, body length, head height, head
width, head heightlhead width, lateral cheek length,
number of post labial annules, stylet length, stylet
base to anterior end, stylet knob
+ stylet shaft
length, stylet knob width, stylet knob length,
DG0
from stylet base, length median bulb, width median
bulb, excretory pore to base median bulb, anterior end to excretory pore, position of hemizonid relative
to excretory pore, anterior end
t.o centre median
bulb, length median bulb “valves”, width median
bulb “valves”, anterior end to hemizonid, length
oesophagus, number of lateral field incisures, width
lateral field, areolation of lateral field, tail length,
tail width at anus, length/width tail, tail shape, caudal ratio
A**, caudal ratio B3’, inflation of rectum
(included because many authors have used
it ; it is
now known (Bird, 1979) to be an artifact, distance
* b = body length : distance from anterior end to
posterior end of œsophageal glands ; b” = body
length : distance from anterior end to centre of median
bulb ; c’ = tail length : body width at anus or cloaca ; d = length tail : body width seen laterally at level of anus ; m = length stylet cone x 100 : stylet length ; O = distance from stylet base to DG0 x 100 : total
stylet Icngth ; T = distance from cloaca to anterior-
most part of testis x 100 : body length. *+ caudal ratio A = length of hyaline tail t.ermina1:
its width at its beginning ; caudal ratio B = length of hyaline tail terminal : width at a point 5 pm from its
terminus.
Revue Nimatol. 6 (2) : 291-309 (1983)
Identification of Meloidogyne
~ ~~______ ~ ~-
phasmids to tail terminus, hyaline tail terminus
length, annule width, anterior end to centre genital primordium, genital primordium to tail terminus.
Females : a, b, b‘, O, ml max. body width, body
length, head width, stylet length, stylet shape, DG0
from stylet base, stylet knob width, stylet lrnob
length, neck length, neck width, body lengthlneck
width, length median bulb, width median bulb, head
to base median bulb, excretory pore to base median
bulb, position of excretory pore relative to stylet
base, anterior end to centre median bulb, length,
median bulb ‘Lvalves”, width median bulb ‘Lvalves”,
annule width ,vulval slit length, interphasmidal distance, level of phasmids to vulva, phasmids
to
anus, centre of vulva’ to anus, length of perivulval
area free of striae, width perivulval area free of
striae, perivulval length/perivulval width,
R;$, Ra*,
perineal pattern.
Eggs : length, width, IengthIwidth.
To assess intraspecific variation, measurements
were made by one operator on freshly fixed males
of
fifteen species and subspecies including three popu-
lations of
M. graminicola. Fresh material was used
because some characters are less easily seen in older
material due to the fixative used and age. Second-
stage juveniles of eleven sp’ecies and subspecies
including four populations of
M. graminicola, two
of
M. graminis and two of M. incoqnita incoqnita
were also measured.
Principal coordinate analysis, a method for finding
coordinates for individuals referred to principal axes
while preserving defined distances between them
(Gower,
19GG), was used as an objective assessment
of the most discriminating characters in males and
juveniles and to show the interrelationships of the
species. Such an analysis makes
no assumptions about
the distribution of the variates in a population.
. LIGI-IT MICROSCOPY OF MALES
Males of 24 species were examined (Tab. 1). With
species which readily produce them, males were more
easily obtained from fresh egg masses of mature
females, rather than by extraction from soil. One
or
several males, depending on the species, were found
to be associated with egg sacs. Males
of some species
* R, = length of dorsal arch base line horizontally
through tail terminus : vertical distance between tail
terminus and dorsal arch line.
R, = length of dorsal arch base line horizontally
through tail terminus : vertical distance between base
line and highest point of dorsal arch line.
Revue Nématol. 6 (2) : 291-309 (1983)
are rare in field collections (e.g. M.. incoqnita) but
can readily be produced in culture by stressing the
host plants by one of the following methods
: i) isola-
tion, over
a period of days, in a beaker, of part of a
washed infected root system. The roots sprayed with
water and males washed to the bottom of the beaker
;
ii) isolation, over a period of days, in a bealrer of
water, of
a complete, washed infected root system
with the aerial parts intact. The water sampled regularly for males
; iii) removal of the aerial parts
of an infected plant leaving the roots in soil. The soil
and roots sampled regularly.
Live males were fixed in TAF (Courtney, Polley
&
Miller, 1955) at about 700 and mounted in TAF.
Fixation and mounting in lactophenol was avoided
because
it sometimes caused the stylet to be obscured
and deterioration occurred with age. Many older
specimens had been rnounted
in glycerol and the
stylet was obscured. Head and stylet morphology were examined only
in lateral view, and micrographs talren using differ-
ential interference contrast illumination (DIC). For
some rare species the only material available for
photography was limited and in poor condition but
al1 the essential features are adequately shown. A key
was constructed using mainly qualitative characters but with a limited number of measurements
; stylet
length, stylet cone length, distance of dorsal oeso-
phageal gland orifice (DGO) from stylet base and
head width.
Results and discussion
CHARACTER ASSESSMENT
The most differential characters, with low coeffi-
cients
of variation as opposed to those with over-
lapping ranges and/or
coefficients of variation
> 20 % are listed in Table 2.
Males
Body length : Intraspecific variation is about12%
on
1 GO0 pm (Tab. 2), however, the use of means and
95 % confidence limits enables groups of species to
be roughly separated into size classes (Tab.
3).
Siylet lengtlr : This is the most differentiating char-
acter because of the broad range in the genus (16-
27 pm) and low coeffkient of variation
(4 %, Tab. 2).
The use of 95 % confidence limits in bivariate plots
with linear characters of limited coeficient of varia-
tion reduces the overlap between species (Fig.
1).
293
S. B. Jepson
Table 1
Male specimens observed by light microscopy.
Species Population Source
acronea
Coetzee, 1956 Malawi RES africana Whitehead, 1960 Kenya ardenensis Santos, 1968 Bristol, U.K. RES arenaria (Neal, 1889) artiellia Franklin, 1961 Wells, Norfolk, U.K. RES camelliae Golden, 1979 (Japan) Beltsville, USA RES ; paratypes 771812, 3, 4. chitwoodi Golden, O'Bannon, Santo & Finley, (Quincy, Washington, USA) paratypes 7712413
1980 Beltsville, USA RES ; USDA paratypes T. 2627-
decalineata Whitehead, 1968 ezigua Goeldi, 1887 grahami Golden & Slana, 1978
graminicola Golden & Birchfield, 1965
graminis Slcdge & Golden, 1964
hapla Chitwood, 1949
incognita incognita (Kofoid &White, 1919) incognita wartellei Golden & Birchfield, 1978
indica Whitehead, 1968 javanica (Treub, 1885)
microtyla Mulvey, Townshend & Potter,
nlegatyla Baldwin & Sasser, 1979 Elizabethtown, N.C., USA USDA paratypes T. 2398 naasi Franklin, 1965 Tytherington, Glos., U.K. RES oryzae Maas, Sanders & Dede, 1978 Surinam ovalis Riffle, 1963 propora Spaull, 1977
undescribed species * Elva River, Russia
1975
Ontario, Canada
RES
; paratype 77/22/2
paratype
Wisconsin,
USA
Aldabra paratypes 77/21/10 RES
holotype 7711211
RES
RES
Kenya
Bolivia
Florence,
S. Carolina,
USA
Beltsville, USA
Bangladesh India
Nepal
Thailand
USA Florida, USA
Maryland, USA
Thetford, Norfolk, U.K.
Montreal, Canada
NCSU, Washington, Loui-
India
Nepal
Iraq
siana, USA T. 2628
holotype 77/10/1
RES
; paratypes 7712317
RES
RES RES
RES
RES RES
RES RES
RES
RES
Al1 material from Rothamsted Slide Collection unless otherwise noted. RES
= in culture at Rothamsted ;
'k M. kralli Jepson, 1983. Revue Nématol. this issue.
NCSU = North
Carolina State University.
294 Revue Ndrnatol. 6 (2) : 291-309 (1983)
Identification of Meloidogyne
Table
2
Differential characters, with coefficients of variation 6 17 yo, for species determination in iMeloidogyne.
Character Average
Number of Order of size for coefficient species character f average of variation variation coefficient
Males
*Body length
*Stylet length *Stylet cone length
*Head shape
*Stylet shape
Stylet knob width
Stylet knob length
Distance of dorsal oesophageal gland
Median bulb ‘valve’ length
Number post labial annules
Number lateral field incisures
Position
of hemizonid relative to
Distance from excretory pore to
orifice
(DGO) from stylet base
excretory pore
anterior end
Second-stage Juveniles
Body length
Stylet length
Stylet knob width Stylet knob length
Distance of DG0 from stylet base
Tail length Distance from excretory pore to
* Tail shape
Number lateral field incisures
Position
of hemizonid relative to
excretory pore
Hyaline tail length *Stylet base to anterior end anterior end
Females
’Stylet shape
Distance of DG0 from stylet base
Stylet knob width
Stylet knob length
Position
of excretory pore relative
to stylet base
*Perineal pattern 15
15
10
9
9 8
15 11
9 8 6 9 8
8
9 8
1 600 f 192 pm 20 f 0.8 pm
4
f 0.3 pm 3 f 0.3 pm
3 f 0.5 pm
5 f 0.5 pm
100 f 10 pm
400
f 16 pm
12 & 0.5 pm 2 0.2 pm
1.5 f 0.2 pm 4 f 0.5 pm
50 f 2.5 pm
70 -l 2.8 pm
15
f 2.1 pm
15 f.0.8 pm
* Most differential characters.
Revue Nématol. 6 (2) : 291-309 (1983) 295
S. B. Jepson
Table 3
Body length size classes in
Meloidogyne males.
800-1 300 pm 1 300-1 700 pm > 1 700 pnz
artiellia
breuicauda Loos, 1953 chitwoodi * exigua jauanica kikuyensis de Grisse, 1960 litoralis Elmiligy, 1968 megatyla
megriensis (Pogosyan, 1971) nzicrotyla * naasi
oteifae Eln~iligy, 1968 ottersoni (Thorne, 1969) propora
tadshilcistanica Kirjanova & Iva-
undescribed spec.ies (Russia)
* nova, 1965
acronea * africana * coffeicola Lordello & Zamith, 1960 ethiopica Whitehead, 1968 grahami ' graminicola * graminis * hapla * incognita incognita incognita wartellei * kirjanovae Terenteva 1965 nzali Itoh, Oshima & Ichinohe, 1969 megatyla
oryzae oualis
querciana
Golden, 1979 sewelli Mulvey & Anderson, 1980
ardenensis * arenaria * camelliae * deconincki Elmiligy, 1968 grahami * incognita wartellei megadora Whitehead, 1968 lucknowica Singh, 1969 spartinae (Rau & Fassuliotis, 1965)
Stylet cone length : This is correlated with stylet
length and in most species the cone
is about half
the stylet length.
M. acronea, M. africana (Fig. 1)
and M. oteifae Elmiligy, 1968 are distinguished by a
cone length of much less than half the stylet length.
Stylet knob width and length : There is much varia-
tion in both characters
(8 % and 11 % on 3 and 4 pm
respectively, Tab.
2), partly due to imprecision in
resolving small differences in size (even with high
resolution optics, which are essential). Measurements
may aid identification in some instances, particularly
in those species with much larger knobs than most
Meloidogyne (e.g. M. megadora, M. megatyla and
M. acronea) but the overall shape of t.he knobs is
more important as a distinguishing feature (e.g. trans-
versely ovoid
; rounded ; backwardly sloping ; taper-
ing ont0 stylet shaft
; set off from stylet shaft).
Distance of DG0 frorn stylet base : Again measure-
ments are subject, to inaccuracy which partly accounts for the large coefficient of variation (17
% on 3 pm,
Tab.
2). While there is much intraspecific variation,
in most species the
DG0 lies between 3 and 6 pm
behind the st,ylet lmobs.
M. acronea and M. arenaria
are distinct, with the DG0 more than 6 Pm(?) behind
the stylet knobs.
It appears that M. mali and
* Aut.hor's measurements, others from literature.
296
M. megadora are similar in this respect with an aver-
age distance from the
DG0 to the stylet base of
8 pm and 6.5 pm respectively (Whitehead, 1968 ;
Ito et al., 1969).
Median bulb LLualue" (= feeding pump lining)
length
: In most Meloidogyne species this value is
about 5 pm with a coefficient of variation of about
10
% (Tab. 2). However, M. acronea, M. africana,
M. hapla, M. jauanica and M. arenaria have some-
what longer LLvalyes" of up to
II Fm.
Number of post-labial annules : There is a single
post-labial annule in most species but because
of the
presence of incomplete annules the condition in
M. incognita and M. arenaria may be variable with
the apparent number depending on their position and the precise orientation of the head. One to three
annules may be seen and each side of the head may
be dissimilar (Eisenback
& Hirschmann, 1980).
Lateral field incisures : Throughout the genus the
basic number
is four, although in the mid region of
the body additional, incomplete incisures may occur :
e.g. ïVI. africana (5), M. ardenensis (5), M. gramini-
cola (6), M. decalirzeata (10) and the undescribed
species (Elva River, Russia)
(5).
Revue Nimatol. 6 (2) : 291-309 (1983)
Identification of Meloidogyne
14
13
12
11
10
9
8
7
6
b+
1
't
16 17 18 19 20 21 22 23 24 25 26 27
STYLET LENGTH pm
Fig. 1. Bivariate plot of stylet length/stylet cone length showing means and 95 % confidence limits for both variates
in 19 species of Meloidogyne. a : acronea, b : africana, c : ardenensis, d : arenaria, e : artiellia, f : camelliae, g : clzit-
woodi, h : grahami, i : graminicola Bangladesh, j : graminicola India, k : graminicola Thailand, 1 : graminis, m : hapla, n : incognita incognita, O : incognita wartellei, p : javanica, q : microtyla, r : naasi, s : ovalis, t : propora, u : indescribed species (Russia).
Position of hernizorzid relative to excretory pore : The distance from stylet base to anterior end, distance
hemizonid is anterior to the excretory pore in most from excretory pore to anterior end and body length.
species, although
it may be close, or posterior to it as The distribution of species about the first four
in
M. grarninis (some individuals), M. hapla (Norfolk principal coordinates reinforced the view that quan-
population) and
M. graminicola (some individuals). titative characters are not exclusively discriminating.
. Distance from excretory pore to anterior end : This Second-stage juveniles
distance is correlated with body length,
but exhibits
greater intraspecific variation (Tab.
2) and is there-
fore less valuable
as a species differentiating char-
Body length ; Juvenile length is less variable than
that
of males (4 % -on 400 ym as opposed to 12 %
,. -4. -.. on 1 600 Pm, Tab. 2) but there is a narrower overall dLbt;l. range for .the genus (275-650 ym, except for M. spar-
Principal coordirzate arzalysis : An analysis using tinae whose range extends to 912 Pm) and overlap
nine characters and seventeen populations showed between species
is considerable. While the use of
that the most important discriminating characters
95 % confidence limits sometimes reduces this over-
are, in decreasing order
of importance, stylet length, lap, differentiation of species remains inadequate.
Revue Ndmatol. 6 (2) : 291-309 (1983) 297
S. B. Jepson
Stylet length
: Stylet length, with a small coeficient
of variation (4
% on 12 pm, Tab. 2) is a good char-
acter only when
it is suficiently well seen for consist-
ent, accurate measurement. In many specimens the
head skeleton obscures the end of the stylet and stylet
length may be underestimated
so it is better not to
use stylet length unless the stylets are made to
protrude by the method of Hooper (1977).
Distance from stylet base to anterior end : This is a
more reliable character than stylet length and also
exhibits a small coeficient of variation
(5 % on
15 pm, Tab. 2). Careful preparation is essential to
avoid displacement of the stylet by contraction of
it,s musculature.
Stylet knob ruidth and length : Measurement of these
characters is of little aid in species determination.
Overall shape
is likely to be of more practical value
as found in males and females, although this has not
been investigated
so far.
Distance of D GO from stylet base : Despite consider-
able variation
(12 % on 4 pm, Tab. 2), species mean
values fa11 between
2-3 pm, 3-4 pm and 4-5 pm and
to this extent the use of 95
% confidence limits may
differentiate groups of species.
M. seruelli is so far
unique with the DG0 7-8 pm behind the stylet base.
Distance of excretory pore to anterior end : While
this character exhibits the same variation as body
length
(4 % on 70 pm and 4 % on 400 pm respect,-
ively, Tab. 2) there is a broader overall range in the
genus and the use of
95 % confidence limits may
improve differentiation of species.
Position of hemizonid relative to excretory pore : In
most species the hemizonid is near
or just anterior to
the excretory pore, although
it is posterior in some
species (e.g.
M. ardenensis, M. grarninis).
Number of lateral field incisures
: As in males the
basic number of lateral field incisures
is four, and
likewise in the mid region of the body there may be
additional incisures
: e.g. M. graminicola (6), M. hapla
(Norfolk population, some individuals) (5) and the
undescribed species (Elva River, Russia) (6).
Tail length : Tail length is a good differentiating
character with a small coeficient
of variation (5 % on
50 pm, Tab.
2). Some species are clearly distinct from
one another in overall range (e.g.
M. graminicola
and M. naasi with long tails, and M. acronea and
M. ardenensis with short tails).
Tail shape : Tail shape is the most useful qualita-
tive character and intraspecific variation
is limited.
The following species and subspecies are examples of
' groups with similar tail morphology (Jepson, in
298 press.)
: M. arenaria, M. chitwoodi, M. hapla, M. java-
nica,
M. incognita incognita and M. incognita ruar-
tellei ; M. graminicola, M. oryzae and M. naasi ;
M. indica, M. artiellia and M. propora. Other species
are unique such as
M. ardenensis. Small differences
occur within the groups which, when considered with
other differential characters of limited variation such
as tail length, distinguish component species.
Hyaline fail length : The hyaline tail length is often
very variable, although in some species
it is clearly
short (e.g.
M. acronea and M. incognita incognifa)
and in others long (e.g. M. graminicola and M. naasi).
Principal coordinate analysis
: An analysis using
ten characters and fourteen populations showed that, of discriminating characters the most important is tail
length and less important are hyaline tail length and
stylet knob width.
As in a similar analysis with males,
the distribution of species about the first four prin-
cipal coordinates showed that even using a combi-
nation of characters most species are not mutually
exclusive.
Fernales
Females have not yet been subjected to the same
morphometric treatment as males and juveniles
;
however, general views on characters used are present- ed here. Stylet length appears to be useful for differ-
entiation because
it exhibits limited intraspecific
variation and there is a broad range, from 10-25 pm,
in the genus. From SEM studies by Eisenback and
Hirschmann (1980) and Eisenback
et al. (1981) of
M. arenaria, M. incognita, M. javanica, and M. hapla
races, and my own which also include M. ardenensis,
M. chitwoodi and M. graminicola, the female stylet
cone, shaft and knobs shape appear to be species-
specific. The differences in stylet knob dimensions
are too small to be of practical value. The range of
the distance from the DG0 to the stylet base is
broad in the genus (2-9 pm) and as in second stage
juveniles, this character may aid differentiation of
species groups. The position of the excretory pore
relative to the base of the stylet may be of use in
some species and subspecies, although
it is very
variable in others (e.g.
M. incognita incoqnifa).
The perineal patterns have been st.ressed in the
past as the most important feature of a species. This
continues to be the case but
1 consider that no
suitable methods for assessing the pattern (such as
that by Esser, Perry
& Taylor, 1976) have yet been
developed.
If perineal patterns are to continue as
major diagnostic features,
it will be crucial to identify
the essential features of a pattern which are stable,
despite overall variation which may be considerable.
Revue Nèrnatol. 6 (2) : 291-309 (1983)
Idenfification of Meloidogyne
~~
Surnrnary of character assesment
The assessment of the characters listed in Table 2
indicates that combinations
of measurements are
useful
as supporting data but are never unequivocal.
The quantitative characters proposed are those of
greatest practical value in terms
of intraspecific
variation and differentiation beLween species, the
aim being
to reduce the number of characters required
for identification to
a minimum. A realistic assess-
ment of the morphological variation in a species
should be made in terms
of component isolates or
populations. Where possible, in this study, quanti-
tative measurements of more than one population,of
a species were made and, on these terms, only the
characters most stable and apparently Ieast influ-
enced by environmental factors are suggested for use
in identification. There is not
a single character which
can be consistently used to the exclusion of al1 others
to imnlediately identify a species but combinations
of those with low coefficients of variation and a broad
range thoughout the genus will serve to differentiate
groups
of species. Many species are alike in some of
the characters, e.g. stylet knob width, stylet knob
length, median bulb valve length
($8 & J2), position
of hemizonid relative
to excretory pore (88 & J2),
number of lateral field incisures
($3 & J2), and posi-
tion of excretory pore relative to stylet base
(qÇ?), and
it is in the few exceptions that the value of the char-
acter is manifest. Conversely, qualitative characters are frequently
species-specific and good examples are to be found
in al1 three stages
: male head shape, male and
female stylet shape, perineal pattern and juvenile
tail shape. Additional characters
of tl& type have
been found with the SEM (Eisenback
& Hirschmann,
1979, 1980
; Eisenback, I-Iirschmann & Triantaphyl-
lou, 1980
; Eisenbacli et al., 1981) although these are
of limited value in the field because the SEM is not
available
to al1 worlrers.
It is essential, as the number of species in the genus
increases beyond 50, that future descriptions are
standard in the characters used, the way in which
these are measured and the illustration
of certain
features (particularly with the use of
DIC light
micrographs and
SEM photographs), and that direct
comparison is made by illustration, with other popu-
lations and species known to be closely related
or of
similar morphology.
LIGHT MICROSCOPY OF MALES AND A KEY TO THEIR
IDENTIFICATION
The characters illustrated are typical for the species
and provide
a basis for comparison. Where possible
Revue Nématol. 6 (2) : 291-309 (1983)
the stability of qualitative characters was confirmed
by examination
of specimens from several different
populations. The key uses mainly qualitative char-
acters but with
a limited number of measurements.
The range
of variation in quantitative characters is
often broad with considerable species overlap al-
though 95
% confidence limits are narrow witll much
less overlap. For this reason, measurements are quot-
ed with confidence limits. Figure
1 showing 95 %
confidence limits of stylet length/stylet cone length
of males illustrates this, although it should be
stressed that except for the three populations
of
M. graminicola, species means are talren from single
populations. Addition
of data from other populations
may extend the range of each species as occured with
M. graminicola.
On the basis of head shape alone, the male heads
of the species of
Meloidogyne considered here form
three groups
with the exception of four of the 24.
The exceptions are three very distinct species
M. acronea, M. javanica and M. propora, and also
M. arenaria, although this resembles species in one
of the larger groups.
Ag. acronea is distinguished by the unique form of
the stylet (Fig. 8). The cone is broad and the shortest
of any known
Meloidogyne species at
(95
% c.l.), with a mean stylet length of 18.06 f
0.19 pm (95 % c.1.). The stylet knobs are large and
pear shaped, resembling.tl~ose
of M. ardenensis, but
taper onto
a much broader shaft (Figs 28 & 29). The
distal opening of Lhe stylet lumen is frequently
obvious. The head outline is ill-defined with a shallow
labial cap and single deep post-labial annule.
M. javanica (Figs 9 & 10) is recognised by the
broad, flattened labial cap. The median lips are
strongly rounded and meet the labial disc al;
a small
indentation on either side of the raised rim of the
stoma. The stylet knobs are transversely ovoid and
the stylet length 20.5
f 0.29 pm.
The distinguishing features
of M. propora (Fig. 11)
are the deep, dome shaped labial cap with the rim
of the stoma raised, the shallow single post-labial
annule and the long slender stylet (23.5
& 0.83 Pm)
with large, broad rounded knobs.
The main groups will be referred
to as Group 1-5
respectively. Group 1 is distinguished by an offset
head (Fig.
3), in which the outline of the head does
not form a smooth contour with the rest of the body
and the neck is more constricted than
in those
individuals without the head offset. The post-labial
annule is approximately three times deeper than the
labial annule. Three species constitute the group.
M. indica and M. artiellia can be distinguished from
M. carnelliae using stylet length (
M. indica and M. artiellia, and > 21.0 pm in
M. camelliae), also the narrower head (
299
S. B. Jepson
a b C
a b C
a b C d
Figs. 2-7. Character of male head and stylet ltnob shape. 2 : head not offset ; 3 : hcad offset ; 4 : labial cap much
narrower across than post-labial annule, post-labial annule distinctly tapéring ante\
riorly, head generally rounded,
a
: labial cap flattened ; b : labial cap distinctly domed ; c : labial cap shallowly rounded ; 5 : head truncate ; 6 : stylet lrnobs and shaft, a : knobs backwardly sloping ; b : knobs set off from shaft ; c : knobs gradually tapering
ont0 shaft ; 7 : shape of individual stylet knobs, a : transversely ovoid ; b : rounded ; c : pear shaped ; d : elongate.
300 Reuue Nématol. 6 (2) : 291-309 (1983)
