Fortuner, Renaud

Horizon / Pleins textes

Morphometrical variability in HeZicotyZenchus Steiner, 1945 
1. The  progeny of a single  fernale (') 
Renaud FORTUNER 
Laboratoire de Nématologie, ORSTOM,  B.P. V-51, A b i d j a n ,  Côte d'Ivoire. 
SUMMARY 
Morphometrical variability in a species of Helicotylenchus was studied in the progeny of a parthenogenetic 
female, probably belonging to Helicotylenchus dihystera. Several criteria currently used in specific diagnoses, and 
particularly  those  describing  the  tail,  were  proved t o  be highly  variable.  Their use in  taxonomical  studies is  discussed. 
RÉSUMÉ 
Variabilitd  morphométrique  chez 'Helicotylenchus Steiner, 1945. 1. La descendance  d'une  seule  femelle 
La variabilité morphométrique intraspécifique chez Helicotylenchus a été évaluée dans la descendance d'une 
femelle parthénogénétiquk du genre, appartenant probablement à l'espèce Helicotylenchus  dihystera. Plusieurs 
critères  couramment  utilisés  dans  la  caractérisation  des  espèces,  et en particulier  ceux  qui se réfèrent à la  queue, 
se sont  révélés  extrêmement  variables.  Leur  usage en taxonomie est discuté. 
Morphological study of nematodes of the 
genus Helicoiylenchus in the ORSTOM (Dakar) 
slide  collection,  representing  specimens  from 
numerous  different  hosts  and  countries  in  Africa, 
demonstrated  that  many  have  the  same  general 
features : spiral  body,  more or less hemispheri- 
cal lip region, body length of 500-900 pin, sty- 
let  length of 24-26 pm,  V-value of 59-65%, 
empty offset spermathecae  and  no males. They 
probably al1 belong to the same species, close 
or identical to Helicotylenchus dihystera (Cobb, 
1893) Sher, 1961. However, in most specimens 
observed, some other criteria, notably those of 
the tail region, e.g. tail .shape, used in 70% of 
specifc diagnoses in  the  genus,  position of phas- 
mids (44% of diagnoses), fusion of inner inci- 
sures, used t o  differentiate H .  dihysteroides Sid- 
diqi,  1972  from H .  dilzystera, for example,  might 
suggest that  these  specimens  belong  to  various 
described  species. 
Altbough the populations from which came 
the observed  specimens  might  have consisted  of 
a mixture of species, to  find mixtures -of the 
same closely related species in  almost  every soi1 
sample  from Africa  seems most  unlikely. 
It was then suggested that some dimensions 
(l) A portion of this  paper was presented at  the  XIIIth  International Nematology  Symposium,  Dublin,  Ireland, 
5-11 September 1976. 
Revue Nématol.  2 (2) : 197-202  (1979) 197 
R. Fortuner 
I 
and  features  used  in  the diagnoses of new  spe-  killed and fixed by FP 4:l (Netscher & Sein- 
cies could represent individual variations within horst, 1969) and mounted in glycerin on Cobb 
the  same species. In  order to  test  this  hypoth- slides. 
esis, variability of those  characteristics was stud- 
ied fronl specimens selected from the progeny 
of a single parthenogenetic female. 
Results 
Material and methods 
Three t o  four rice (cv.  1-Kong-Pao)  seeds  were 
sown in each of 45 pots containing heat steril- 
ized soil, protected from contamination by plas- , 
t ic '  Shields. After two weeks, each of 20 pots 
were inoculated  with one female of Helicotylen- 
chus originating from a field in Senegal with a 
maize - upland rice - peanut rotation (Inor 
Mandingue ; sample number 162 in Fortuner, 
1975).  The  other  25  pots,  left  non-inoculated as 
controls, were intermixed with the inoculated 
ones. After six months, the nematodes present 
in  the soil of the  pots were  extracted  by  elutri- 
ation and examined. Some pots were discarded 
because of contamination of controls,  others  for 
inoc.ulation failure,  but one pot was found con- 
taining numerous specimens of Helicotylenchus 
and was probably free of contamination, as the 
adjacent  controls  contained  no  nematodes.  From 
this pot 45 females were selected at random, 
QUANTITATIVE MEASUREMENTS 
Range, mean, standard deviation and coef- 
ficient of variability  were  calculated  for  the fol- 
lowing  criteria : lengths of body,  stylet,  anterior 
part of stylet, oesophagus (to oesophago-intes- 
tinal  junction  and t o  base of glands),  tail ; dis- 
tances  from  head to  vulva  and  from  dorsal  gland 
opening  to  stylet  knobs  ;-anal  and  vulval  body 
diameters ; number of 'tail  annules  and  positions 
of inner incisures fusion and of phasmids. Re- 
sults  are given in  Table 1. 
Stylet  length was the  most  constant measure- 
ment (C.V. = 1.7%) ; total length, length of 
oesophagus  measured  to'  oesophago-intestinal 
junction, anal and vulval body diameters were 
also  reliable (C.V. = 3.2 to  4.5%).  On  the  other 
hand,  criteria  related t o  tail, viz. tail length, 
nunlber of tail  annules,  position of fusion of in- 
ner  lateral field incisures and position of phas- 
mids had rather high coeflicients of variability 
(C.V. = 9.6 to  70%). 
Table 1 
Morphometric  characteristics  in  the  progeny of a single Helicotylenchrts female (n = 45 Q) 
Cri ter ia   Range   Mean  S tandard  Coel.ficient 
(Pm)  (Fm) deviation of variation 
Stylet  length 23.5-25 24.5  0.4  1.7 
Anterior  part of stylet 9.5-10.5 10.2 O ..3 3.2 
Total  length 623-751 671 25 3.7 
Oesophagus  length  (to  valve) 103-121 111 4.2 3.7 
Head  to  vulva  distance 389-461 417 16 3.9 
Anal  diameter 13.5-16.5 15 0.67  4.5 
Vulval  diameter 21-25.5 23.5  1.0 % 4.5 
Oesophagus  length ( t o  base of glands) 110-147 129 7.5 5.8 
Tai1 length 17.5-26.5 20.9  2  9.6 
Number of tail  annules 11-17 13.5  1.5 11.4 
Dist.  d.  gland  opening  to  knobs 6-11.5 9.3  .4 15 
Inner  incisures  fusion  (in  tail  annules  from  anus), 1-11 7.5 2  26.7 
Phasmids (in tail annules from' anus ; + if anteriad) . -3 +6 $2.8 1.9 70 
- - - .  ---- - _ - - -  -- - - -  - .-. -. -__ _ .___ _ ~ _ _  __ - .~ -~ - _ _ _ _  
198 Revue Nématol. 2 ( 2 )  : 197-202 (1979)
Variabi l i ty  in Ilelicotylenchus 
RATIOS 
The validity of the usual ratios (a, b, b’, c, 
c’, V, O and ln) was tested  by a t-test (Roggen 
& Asselherg,  1971) with : 
t =  cvy - cvx 
q c v ;  + cv: 
2n 
where CVx and C V y  are  the  coeficients of varia- 
bility of the  terms of the  ratio  and n the  number 
of observations (here n = 45). The degrees of 
freedoln are 2n - 2 = 88. Results are given in 
Table 2. 
Ratios  b’,  c,  c’,  m  and O are  formed  with 
measurements the coeffkients of variability of 
which are significantly different (a t  1 y0 level) 
and tlzus are statistically un,iustified. Ratios a, 
b and V are justified and were calculated (Ta- 
ble 3). 
Table 2 
t-test of the significance of the difference  between coefficients of variability ( n  = 45) 
Ratios  
a = body length/vulval diameter 
b = body length/oesophagus (to valve) 
b’ = body  length/oesophagus  (to  glands) 
c, = body length/tail length 
c’ = tail  lengthlanal  body  diameter 
V = dist.  head t o  vulvalbody  length 
m = ant.  part  stylet/stylet  length 
O = dist d.g.0. to knobs/stylet length 
~ 
Coeff. uar. 
3.7145 
3.713.7 
3.715.8 
3.719.6 
9.614.5 
3.913.7 
3.211.7 
15.0/1.7 
1.303 
O 
2.896 
5.440 
4.563 
0.353 
3.927 
8.358 
- 7  
4- + + 
+ + 
- 
QUALITATIVE CRITERIA 
Table 3 
Variability of ratios  in  the  progeny 
of a single Helicotylenchus female 
Rat ios   ngeMean   S t ndard  Coefficient 
deviation of variation 
a 26.2-3 1.8 28.6 1.36 4.8 
b 5.6- 6.7 6 0.24  3.9 
V 58.6-65.6 62.1 1.4 3.3 
It can be noticed that  no  reduction of varia- 
bility was obtained with ratios a and b. Only 
ratio V is both justified and useful : its C.V. is 
2.3%, better  than  the C.V. for body  lengtll 
(3.7%) and for head to vulva distance (3.9%). 
This species of Helicotylenchus apgears to be 
exclusively parthenogenetic : no male having 
been observed among the thousands of indivi- 
duals  obtained  from field samples, and  only 
empty spermathecae having been seen in the 
hundreds of fixed females studied for specific 
determinations. 
Other characters were also very constant : 
body  shape  spiral  in fixed  specimens,  offset  sper- 1 
matheca, hemispherical  lips  with  labial dise non- 
visible with transmitted light microscope, oval 
median  oesophageal  bulb  never iilling the  body 
cavity,  position of hemizonid and  excretory  pore 
always  anterior  to  oesophago-intestinal  junction, 
and absence of fasciculi (‘canals’). Al1 of these 
criteria  were  observed  in  each of the 45 females 
studied. 
Shape of stylet  knobs was more  variable,  from 
anteriorly  indented  to  flattened  or  rounded.  Lip 
Revue Nénzatol. 2 (2 )  : 197-202 (1979) 199 
R. Fortuner 8 
200 Revue  Némaiol. 2 (2) : 197-202 (1979) 
Variabi l i ty  in Helicotylenchus 
annulation, generally present, could not be de- 
tected  on some  specimens. 
However the  most  variable  criterion  was  the 
shape of the tail and related features. Figure 1 
illustrates various tail shapes observed within 
the females studied. Tai1 l g  is identical to the 
typical  tail of Helicotylerzclzus dilzystera as illus- 
trated  in Fig.  1B of Sher  (1966), Fig.' 3C of Roman 
(1965),  Fig.  H  and 1 of Siddiqi  (1972 b ) ,  Fig.  6G 
of Anderson  (l974),  Fig. 1F of Sauer  and  Winoto 
(1975) and Fig. 8f of Van den Berg and  Heyns 
(1975). 
Other  tails  in  the  present figure resemble H .  
dilzystera tail variations as described by these 
authors : the sequence w-x-y is similar to tails 
D, E ,  F, and G of Siddiqi (1972 b ) ,  Fig. 6H 
and 61 of Anderson (1974), Fig. 1E and 1G of 
Sauer and Winoto (1975) and Fig. 8d, 8c and 
8i of Van den Berg and Heyns (1975) ; series 
1-p-t-u is similar to tails in Fig. 2F and 2H of 
Ali, Geraert and Coomans (1973), and tail y t o  
Fig.  3B  and  3D of Roman  (1965). 
Some tail shapes illustrated in Figure 1 are 
also yuite similar t o  those of other described 
species. For esample,  the series  v-w-x-y  res- 
sembles H .  cauenessi Sher, 1966 (Fig. 6E)., II. 
elegarzs RomAn,  1965 (Fig.  6D), II. cariberzsis 
Roman, 1965  (Fig.  2D), H .  digolzicus Perry, 
1959 (as redescribed by  Sher, 1966, Fig.  2G, 2H), 
H. paraconcauus Rashid & Khan, 1974 (Fig. 2C, 
2D), H .  aerolatus Van den Berg & Heyns, 1975 
(Fig.  le). Series r-s is  similar to H .  flatus Roman, 
1965  (Fig.  7D), H .  borinquerzsis Roman,  1965 
(Fig.  7F), FI. glissus Thorne & Malek,  1968 (Fig. 
26F, 26G), and H .  barnbesae Elmiligy, 1970 (as 
redescribed by Ali and Geraert, 1975, Fig. I I ,  
lJ, 1K and 1L). Series j-k-1 resembles H .  talo- 
n u s  Siddiqi,  1972 a (Fig. 2R',  2S, 2T). H .  talonus 
in Fig. 2P, 2Q is also identical with series r-S. 
Series j-k-1 resembles H .  dilzysteroides (Fig. lA, 
1F) and tail c is similar to H .  pseudorobustus 
(Steiner, 1914) Golden, 1956 (as redescribed by 
Sher, 1966, Fig. 10, 1P). 
In  addition  to  variations of tail  shape,  length, 
thickness, shape and position of the terminal 
process, curvature of the ventral side of tail, 
length of inner incisure fusion and position of 
phasmids varied greatly from one specimen to 
the  other.  The  dorsal  tail  annules were generally 
identical to  the  body ones, but sometimes  small- 
er  or  larger. 
Revue  Nématol .  2 (2) : 197-202 (1979) 
Discussion 
Study of a strain from a single female culti- 
vated  in one pot  (with  minimum  variations be- 
tween specimens concerning environmental fac- 
tors) showed that  many  criteria  currently used 
in  taxonomy of Helicotylenchus are  highly 
variable. . 
This is particularly  true for tail  shape.  Intra- 
specific variability of this feature has already 
been demonstrated  for  many  genera : eg. Cylilz- 
drocorpus (Chin,  1975)', Xiphinerna  (Luc & Hunt, 
1978), Paratyle~zchus (Geraert,  1965)  and P r a -  
tylerzchus (Taylor & Jenkins,  1957).  Among  spe- 
cies of Helicotylerzchus, tail  variability  was  men- 
tioned by several authors (eg. Sher, 1966 '; Sicl- 
diqi, 1972 a ; Anderson, 1974, Van den Berg & 
Heyns,  1975).  However 1 believe that this is 
the first  time that  the single  female inoculation 
method (used by Van Weerdt (1958) for Rado- 
pholus   s imil is;  Loof (1960)  for Pratyle~zchus 
neglectus; Goodey and Hooper (1965) for A p h e -  
lerzchus auerzae, and others) has been used for 
assessment of variability in Helicotylerzclzus. It 
must be stressed that  every  tail  shape  in  Fig. 1 
was  observed  in  the  progeny of a single female 
and that it is possible to find a graded series 
of tail shapes for example from the typical W. 
dihystera shape  (g)  to  an II. putus-type  tail  (r,s) : 
g-f-e-d-c-b-i-k-n-r-s. The wide range of shapes 
observed here is then al1 the more meaningful 
and suggests strongly that differences of tail 
shape  should  not be used for differentiating be- 
tween  most of the species of Helicotylenchus,  and 
particularly  those  mentioned  in  the  present 
article. 
Additional  studies of this  type should  be  made 
comparing closely related described spec,ies of 
Helicotylenchus, to  ascertain  the  extent of varia- 
bility of diagnostic characters, their degree of 
overlap,  and  ultimately  the  validity of the spe- 
cies involved. 
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Morphometrical variability in Helicotylenchus Steiner, 1945 : 1 - The progeny of a single female

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