Vovlas, N.

Horizon / Pleins textes

Parasitism of Trophotylenchulus obscurus on coffee roots 
Nicola VOVLAS 
Istituto d i  Nenzatologia Agraria, C.N.R., Via G. Arnendola 165/A, 70126 Bari, Italy. 
SUMMARY 
Trophotylenchulus  obscurus (Colbran,  1961)  Cohn & Kaplan,  1983 is a  widespread  Pest  of  coffee (Coffea arabica L.) in SPo Tomé, 
West  Mrica. The nematode  has  semiendoparasitic  habits  and  induces the formation  of  dark  capsule-like  structures  which  protude 
from  the  root  surface.  These  capsules  protect  the  nematode  life  stages  attached  to the roots.  Histological  examination  of  coffee 
roots  infected  with  mature  females  indicated  they  established a permanent  feeding  site in a  single  cortical  cell. This single  nurse 
ce11  was the same  size  as  adjacent  cells, but had  dense  cytoplasm  and  an  enlarged  nucleus and  prominent  nucleolus. A large  vacuole 
was  observed in senescent  nurse  cells. The single  nurse  cell  of T. obscuruswas similar to Trophotyle,lch.z~luspondensisand Tylenchulus 
semipenetrans nurse  cells  which  are  formed in clusters in the  root  stele  and  cortex,  respectively. 
Le parasitisme de Trophotylenchulus  obscurus envers les racines de caféier 
Trophotylenchulus  obscurus (Colbran,  1961)  Cohn & Kaplan,  1983  est  un  parasite  très  commun  du  caféier (Coflea arabica L.) 
à SB0 Tomé,  Afrique  de  l'Ouest. Le nématode  est un  semiendoparasite  qui  induit  la  formation  de  corps  capsulaires  noirâtres qui 
saillent a la  surface  de  la  racine.  Ces  capsules  protégent  les  diffkrents  stades u nématode Fiés sur les  racines.  L'étude  histologique 
des  racines du caféier  infestées  par  des  femelles  matures  a  montré  que  celles-ci  sont  en  relation  avec un site  nutritionnel  localisé 
dans  une  seule  cellule  corticale.  Cette  unique  cellule  nourricière  est  de  même  taille que les  cellules  voisines,  mais  son  cytoplasme 
est  plus  dense,  le  noyau  plus  grand et le  nucléole très développé.  Une  grande  vacuole  a  été  observée  dans  les  cellules  nourricières 
sénescentes.  Cette  cellule  nourricière  unique  de T. obscurus est  semblable  aux  cellules  nourricières  de Trophotylenchulus~oridensis 
et de TylencRuZus senzipenetrans lesquelles  sont  formées  en  groupes  dans  le  cylindre  central  et  le  cortex  radiculaire,  respectivement. 
Trophotylenchulus obscurus (Colbran, 1961) Cohn & 
Kaplan, 1983 has  been  reported  in  Australia, where it 
was first  described on roots of Hodgkinsonia  jkescens 
C. T. White, in Cameroon and Kenya on several hosts 
and recently in SZo Tomé  on coffee (CofSea  arabica L.) 
roots (Colbran, 1961 ; Samsoen & Ali, 1978; Volvas & 
Lamberti, 1985). Of  the  members of the Tylenchulidae, 
only the parasitic  habits of Sphaeronema  rumicis 
Kirjanova, Trophotylenchulus floridensis (Raski) Cohn 
Kaplan  and Tylenchulus  sellzipenetrans Cobb have been 
studied (Van Gundy, 1958; Cohn & Kaplan,  1983; 
Volvas & Inserra, 1986). Little  information exists on  the 
parasitism of T. obscurus on  its  hosts. The objectives of 
this  study were : a) to determine the mode of parasitism 
of i7 obscurus on coffee and b) to compare the histo- 
pathology of coffee  roots  infected  with  this  nematode 
with that induced by T. floridensis on, Pinus  clausa 
(Chapm.) Vasey reported by Cohn and  Kaplan (1983) 
with that induced by T. sewipenetrans on citrus roots. 
Materials  and  methods 
Coffee  roots  infected  with T. obscurus, collected from 
a coffee plantation in SZo Tomé (West Africa) were 
gently washed free of  soi1 and  cut  in segments 4-5 mm 
long. Some roots were fixed in 2.5 O/O formaldehyde 
solution and observed with a  stereo-microscope.  Others 
were fixed in FM,  dehydrated in a  tertiary  butyl alcohol 
series and embedded in paraffin. Embedded roots were 
sectioned at 10 Pm, stained with safranin  and fast green, 
mounted in Dammar xylene, and  examined  with  a 
compound microscope  (Johansen, 1940). Sections of T. 
semipenetrans infected rough-lemon (Citrus lenzon L. 
Burm. F.) roots were obtained  with the same  procedure 
and utilized  for  comparative histological observations. 
Results  and  discussion 
Trophotylenchulus  obscurus is a  semiendoparasite  with 
vermiform  second  stage juveniles (J2) (Figs 2,  3). They 
penetrate  coffee  roots  approximately 5-8 O/o of the body 
length. The remaining body portion  protrudes  outside 
the root.  Adult  females  are  sedentary with swollen 
posterior  body  (Figs 5,  12). A mature  female  produces 
a gelatinous matrix in which the eggs are deposited. 
From 25 to 50 eggs were observed in each  egg mass. A 
characteristic  feature of T. obscurus on coffee, similar to 
reports from  other hosts (Colbran, 1961; Samsoen & Ali, 
Revue Nématol. 10 (3) : 337-342 (1987) 337 
N. Vovlas 
338 
Figs 1-5. Coffee  roots  infected  with Trophotylenchulus  obscurus and  life  stages  of  nematode. 
1 : Dark  brown  capsules (C) protuding  from  the  root  surface. 2 : Mature capsule  separated 
from the root  showing  a  dark  capsule Wall (CW); egg (E); juvenile (J) and  an  adult  female 
( Q ). 3 : Newly  hatched  juvenile. 4 : Anterior  end  of  a  juvenile. 5 : Posterior  body  portion 
of T. obsczmls adult  female  (Scale  bar = 250 pm in Fig. 1; 50 pm in Figs 2-5). 
Revue Ninzatol. 10 (3) : 337-342 (19871 
Trophotylenchulus  obscurus on coffee roots 
' Figs 6-1 1. Histological alterations induced by Trophotylenchulus obscurus in coffee roots. 6 : 
Cross  section  with  a  female  nematode (N) partially  covered  by  a  capsule  (CW). The anterior 
body  portion  has  penetrated  into  the  peripheral  layers  of the cortex  and  the  nematode  feeds 
from  a  single  nurse ce11 (FC); EP = epidermis. 7 : Cross  section  showing two nematodes 
(N) in the  cortex.  Note the single  nurse ce11 with  dark  stained  cytoplasm  and the prominent 
nucleolus  (nu). EP = epidermis. 8 : Cross  section  showing  a  nematode (N) feeding  from 
a single nurse ce11 (FC). Note two empty hypodermal cells with a portion of the Wall 
abnormally  thickned (TW). 9 : Cross  section  showing  a  nematode  (N)  feeding  from  a  single 
nurse ce11 in early  phase  of  senescence  and  with  a  vacuole (v) in phase of formation. Nu 
= nucleus;  st = nematode  stylet. 10 : Cross  section  showing a nematode (N)  feeding  from 
a senescent nurse ce11 with a large vacuole (v). 11 : Cross section showing nematode (N) 
feeding  from  a  nurse ce11 in advanced  phase  of  senescence in which  only  a  small  amount of 
cytoplasm  is  left.  Note the abnormally  thickened (TW) ce11 Wall (Scale  bar = 30 Pm). 
Revue Nématol. 10 (3) : 337-342  (1987) 339 
N. Vovlas 
Figs  12-17.  Tai1  regions  of T. obscurus and T. sernipenetrans and  outstanding  differences  in 
their mode  of  parasitism.  12, 13 : Differences on obesity,  position  of  vulvas (V) and  excretory 
pores  (EP)  of T. obscurus (with  coiled  postvulval  portion  in  Fig.  12  and T. sernipenetrans  with 
straight  and  short  postvulval  portion in Fig.  13).  14,  15 : Cross  section  of  coffee and  rough 
lemon  roots  showing the different  depth of  body  penetration in host  tissues  of T. obscunls 
(in Fig. 14) and T. semipenetruns (in Fig. 15). ENC = degenerate empty nurse cells; FC 
= feeding cell; EN = endodermis. 16, 17 : Details of T. obscurus (N) single feeding ce11 
(SFC) in Fig.  16  and  cluster  of  nurse  cells (CN) of T. Semipenetruns(N)  respectively on coffee 
and  rough  lemon  roots. EP = epidermis  (Scale  bar = 30 Pm). 
340 Revue  Nématol. 10 (3) : 337-342 (1987) 
Trophotylenchulus  obscurus on coffee roots 
1978) was the  formation of a  protective,  subspherical, 
dark brown capsule that covered the posterior body 
portion of the nematode infective stages (Figs 1, 2). 
These capsules were similar to those describe for T. 
jloridensis infected Pinus clausa roots; T. mangenoti 
infected Dorstenia  embergeriroots and T. piperisinfected 
Piper  nigrunz roots  (Luc,  1957; Cohn & Kaplan,  1983; 
Mohandas, Ramana & Raski, 1985). Capsules with 
mature  females were easily detached from  the root  and 
were from 200 to 300 p in diam. The capsules 
contained eggs, juveniles and males in the gelatinous 
matrix (Fig. 2). 
Histological examination of coffee  root cross sections 
infected  with T. obscurus mature females  indicated 
(Figs 6 to 14) they penetrated the epidermis and the 
peripheral layers of cortical cells, three to four layers 
deep,  and  established  permanent  feeding sites in a single 
cortical cell. The nematode fed from one modified 
cortical ce11 (Figs 6,  7,  14). This discrete single ce11 was 
the same size as adjacent  cortical cells, but had  dense 
cytoplasm and enlarged  nucleus  with  prominent  nucleo- 
lus (Fig. 7). The hypertrophied nucleus was oval in 
shape, two to  three  times  larger than normal  cortical ce11 
nuclei.  Presence of a large vacuole was observed in  some 
nurse cells, indicating  senescence  (Figs 9, 10, 11). 
Aging of single nurse cells resulted in increased vacuole 
size. The enlargement of the vacuole forced the dark 
stained  cytoplasm in  the portion of the ce11 adjacent to 
the feeding  site  (Figs 10,  11). Ce11 walls  were abnormally 
thickened  (usually  hypodermal cells) at  the  feeding  site 
and in senescent single nurse cells. Empty nurse cells 
with a portion of ce11 Wall (usually the external one) 
abnormally  thickened were observed  adjacent to active 
nurse cells with dark  stained  cytoplasm (Figs 8, 11). 
The single nurse ce11 induced by T. obscurus was 
similar to  the  nurse cells of T. jloridensis and T. senzipene- 
tram (Van Gundy,  1958;  Cohn & Kaplan, 1983). The 
common feature of the nurse cells induced by these 
nematodes is the absence of ce11 hypertrophy and the 
dense cytoplasm with single hypertrophied  nucleus  and 
nucleolus; T. obscurus is a  cortical ce11 feeder, but 
produces only a single nurse cell, unlike T. senzipenetrans 
that forms a cluster of four to six nurse cells. The 
parasitic  habit of I: senzipenetrans (Figs 15,  16, 17) 
observed  on Citrus  lemon roots  did not Vary from  what 
has  been previously described (Van Gundy & IGrkpa- 
trick, 1964; Cohn, 1965; Inserra, Vovlas & O'Bannon, 
1980; Kaplan, 198l),  although  different  depths of corti- 
cal penetration by the nematode body were observed 
(Figs 16,  17). Nurse cells, four  to five in  number  in cross 
section view, were usually  observed in interna1 cortical 
ce11 layers and  in some cases adjacent to  the  endodermis 
(Fig. 16). 
The parasitic habits of T. obscurus apparently seem 
similar to T. senzipenetrans, but the two nematodes, 
although both cortical feeders, show substantial differ- 
Revue Néntatol. IO (3) : 337-342  (1987) 
ences in  the degree of root  body  penetration and 
number of nurse  cells involved in the  nematode  feeding 
(Figs  14 to 21). Deeper  differences on cellular  responses 
exist also  between T. obscurus and T. jlondensis. T. 
jloridensis is a  stelar  feeder, which causes the  formation 
of a  small number of discrete  nurse cells in  the stelar 
parenchyma  (Cohn & Kaplan, 1983). 
Different  host  responses  are  uncommon  among 
plant-parasitic  nematode species of the same  genus. So 
far, in addition to Trophotylenchulus, the only other 
genus known to  produce  different  cellular  response is 
Rotylenchulus (Volvas, Cohn & Inserra, 1985). 
The above illustrated characteristics and the sche- 
matic representation in Figures 18-21 of the mode of 
parasitism of T. obscurus and T. senzipenetrans may  be 
of additional  diagnostic value in  the differentiation 
between Trophotylenchulus and Tylenchulus, and sup- 
port  the placing of I: obscurus to  the  genus Trophotylen- 
chulus as  proposed by Cohn  and  Kaplan (1983). 
ACKNOWLEDGMENTS 
1 am very  grateful to  Prof. F. Lamberti for providing Tropho- 
tylenchulus  obscurus parasitized  plant  material  and  Drs. R. N. 
Inserra,  J. H. O'Bannon  and E. Cohn  for  their  kind  sugges- 
tions  during the preparation of the  manuscript. 
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Figs  18-21.  Schematic  representation  of  host ce11 modifications  induced  by Trophotylenchulus 
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342 Revue Nérnatol. 10 (3) : 337-342 (1987) 


Parasitism of Trophotylenchulus obscurus on coffee roots

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