Demeure, Yves

Name not available

Biology of the plant-parasitic nematode Scutellonema cavenessi Sher, 1964 : anhydrobiosis

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Biology of the plant-parasitic  nematode 
Scutellonema cavetzessi Sher, 1964 : anhydrobiosis 
Yves DEMEURE 
Laboratoire de Nématologie, ORSTOM, B.P. 1386, 
Dakar. Sénégal . 
SUMMARY 
Female,  male  and  larvae  (3rd  stage - 4th  stage) of Scutellonerna cauenessi are able to  survive  in  dry soil for as 
long as nine  months.  Observations  suggest that  a migration  from the higher dry  depths  to the lower more moist 
depths did not  take place.  Nematodes extracted  from  dry soil  were  found to  have  tightly’coiled spiral shape  charac- 
teristic for anhydrobiotic  nematodes,  Anhydrobiotic coiling  in S. cauenessi has  been  induced in uitro, in a relative 
humidity  chamber  and 88 y. can be revived  after one month in a desiccator a t  O y. relative  humidity. 
RÉSUMB 
Biologie du nématode  phytoparasite Scutellonema  cavenessi Sher,  1964 : anhydrobiose 
Scutellonerna  cavenessi survit  dans  un sol, sans  plante  hôte, à une  période  de  sécheresse  de 9 mois  dans la propor- 
tion  de50 %; chacun  des  stades  de  ce’nématode (femelle,  mâle et larves  de 3eme et 4eme stade)  survit  dans de  semblables 
proportions.  La  majorité des  individus  de la population  de S. cauenessi est  localisée au  niveau 0-20 cm où les  condi- 
tions environnantes (température, teneur en eau) sont extrêmement sévères. Aucun phénomène migratoire de 
l’horizon 0-20 cm  vers  l’horizon 20-40 cm  n’a  pu  êire  enregistré  pendant la durée  de  nos  observations. En sol sec, 
femelles,  mâles et larves  de S. cauenessi adoptent  un  habitus  spiralé ; cette  conformation  est à. mettre en relation 
avec  un  état  anhydrobiotique ( =  état  résistant à l’environnement  déficitaire en eau).  Cette  spiralisation  anhydro- 
biotique a pu être  induite in uitro chez 83,5 y. des  individus  d’une  population  de S. cavenessi et 88 Y. de ces individus 
spiralés  survivent à une  exposition  d’un mois à.O % d’humidité  relative. 
During  the  rainy  season of the Senegalese 
Sahel  (from  june t o  september)  just  enough 
water (400-600 mm) is precipitated t o  allow the 
culture of one  crop.  Among t.he main  crops 
grown,  groundnut,  millet  and.  sorghum  are  often 
parasitized  by  the  nematode Scutellonema caue- 
nessi Sher, 1964. 
During the nine months following the rainy 
season the soil is subjected to severe desicca- 
tion ; therefore,  the  nematode  either  escapes 
severe  drought or possesses some  means  to 
resist  desiccation.  There  are at  least  two  means 
by which nematodes  may  survive, one is  in 
perannual  hosts  adapted  to  this  dry  climate  and 
the other is by migration of the  nematodes  to 
lower depths  in  the soil which  are  subjected t o  
less desiccation.  Previous  studies  (Demeure, 
1975, 1978)  have  demonstrated  the  existence 
of anhydrobiotic mechanisms which might en- 
able S. cavenessi to resist desiccation in s i tu .  
Revue   Nématol .  3 (2): 283-289 (1980) 283 
Y .  Demeure 
Such a phenomenon  either  combined  with 
migration  or  plant  association, could explain 
the survival of this nematode under the stress 
of the  dry climate  conditions. 
In  this  paper  the  results of field observations 
on  the  migration of S. cavenessi made a t  regular 
intervals  during  the  dry  season  are  given. 
Further the response of this nematode to slow 
desiccation in vitro, using  a  technique devel’oped 
by  Demeure,  Freckman  and  Van  Gundy (1979b) 
is reported. 
Material  and  methods 
Soil samples were taken from a field at the 
Experimental  Station of the  ISRA  (Institut 
Sénégalais de Recherches Agronomiques, Bam- 
bey,  Senegal).  During  the  previous  rainy season 
this field was  cropped  with  groundnut. Compo- 
sition of the soil was : Sand 85c/,, silt : 7%  and 
Clay : 8%. 
Soil samples  were taken  at  monthly  intervals 
beginning on october 15th 1975, a date corre- 
sponding with the last rainu of’ the year, and 
continued until july 15th 1976 when the first 
rainfall of t,he  new  crop  season  took  place. 
Between these two dates rainfall was 1.1 mm 
(Tab. 1). 
Table 1 
Rainfall  over the period of the experiment 
(CNRA, Bambey  Experimental  Station), 
mm  per month 
October 1975 
November R 
December D 
January 1976 
February 
March 0 
April B 
May 4 
June )) 
July )) 
7 
O 
O 
0.8 
O 
0.3 
O 
O 
1.8 
101 
Samples  were taken  from  two soil depths, 
the  first  layer  from 0-20 cm  and  the second 20- 
40 cm.  To  avoid  mixing the soil of the  two  depths 
two  suffkiently  deep  trenches,  rectangular  in 
section, one meter long and 50 cm wide were 
- -. ~ - -  dug  at places  chosen a t  - random ... .- in  the . field. - 
284 
Samples  were  taken from  each of the  four walls 
of each  trench. 
Nematodes were extracted using elutriation 
techniques developed by Seinhorst  (1956,  1962). 
To  observe  anhydrobiotic S. cavenessi, nema- 
todes were extracted from soil by  a  sugar  flota- 
tion  technique,  using  1.25 M sucrose (Freckman, 
Kaplan & Van  Gundy,  1977).  The  total  number 
of S. cavenessi extracted was counted using a 
dissect,ing microscope. 
The soil moisture content of soil from both 
depths sampled was  calculated  from the loss 
of weight of soil samples placed in  an  oven  at 
1050 for  24  hours. 
Soil temperatures  at 10 Cm and  50  cm  depths 
were obtained from the meteorology section of 
the  ISRA  Bambey. 
Resistance t o  drought was also studied by 
submiting S .  cavenessi t o  air  maintained a t  low 
relative humidity. Eight lots, each consisLing 
of 100  hand pickecl nematodes,  placed  in  water 
were concentrated on a Millipore @ filter each 
and placed in a humidity chamber where they 
were  exposed to slow desicxation using a modi- 
fication of Simons’ dehydration schedule (De- 
meure, Freckman & Van Gundy, 1979). Nema- 
todes  were  exposed for two  days a t  each of the 
following relative  humidities : l O O % ,  99.4%, 
98.8% and  97.7%.  .After  the  nematodes  had 
been exposed for two days t o  97.7% relative 
humidity,  four of the  batches  were  returned 
to  optimal  moisture  by  placing  the Millipore 
filter in a dish with a film of wat,er ; the  other 
four  eplicates were exposed to 0% relative 
humidity by placing the filter in a desiccator 
filled with (SiO,), for 24 hours before plac,ing 
them in a film of water.  In  an  other  experiment 
the same procedure was followed but  this  time 
the  nematodes were kept  at 0% relative humi- 
dit,y during 30 days.  Temperature for these 
experiments was maintained at, 280. Al1 expe- 
riments were repeated  twice.  Populations of 
S. cavenessi in al1 experiments were composed 
of larvae (La and L4) and of males  and  females. 
Survival of nematodes was determined by  count- 
ing  individuals  actively  moving  after  having 
been  placed in  water  for 48 hours.  The  percent- 
age of coiling was determined by counting the 
number of coiled nematodes  on  the  filter  directly 
under  the microscope. 
. - - - - -  -~ . _ -  - _ _  
Revue  Nématol. 3 (2): 283-289 (1980) 
Anhydrohiosis in Scutellonema  cavenessi 
1000 cm3 soi! Scutellonema cavenessi / 
3000 
O - 20 cm  depth 
2000 
1000 1 ,  ~ 
.. .. .. .. .. 
I I 
june oct. , nov. dec. jan. feb. ma r. apr. 
1975 1976 
1 Scutellonema cavenessi / 1000 cm3 soi1 
500 1 20-40 cm depth 
1975 1976 
Fig. 1. Size of the  population of Scutellonema  cavenessi (fernale,  male, larvae)  during  the  dry  season  (October 1975- 
July 1976) a t  0-20 cm  depth  and 20-40 cm  depth. 
Revue Nkmatol. 3 ( 2 )  : 283-289 (1980) 285 
Y .  Demeure 
Nematodes extracted by the sugar flotation 
technique  were  photographed  in a drop of sugar 
1.25 M. Photographs of nematodes taken from 
Millipore filter  were  placed in 5% formaldehyde 
(Freckman, Kaplan & Van Gundy, 1977). Al1 
photographs were taken with a Leitz “Ortho- 
mat” photomicroscope. 
Results 
During the drx season the number of indi- 
viduals of al1 stages decreases progressively to 
about  50% of the  number of nematodes in July 
compared to   that  found  in  October.  This  obser- 
vation was made  in  both  depths  studied  (Fig. 1). 
Comparing the  number of individuals of the 
different stages observed in both depths it is 
evident  that  at  any  time  the  number of nema- 
todes in the lower depth is lower than  that   in 
the upper depth (5 t o  10% of the number of 
individuals in the upper depth). Second stage 
larvae  and eggs were never extracted from soil 
during  the  dry  season.  During  the  dry  period of 
the  year  90 %-95 % of S. cavenessi ( females,  males 
and larvae) extracted were coiled (Fig. 3 A-C). 
Soil moisture content in the upper 20 cm of 
soil deweases  rapidly  during  the  first  month 
after the last rain and remains stable for the 
rest of the  dry season (0.3%)  (Fig. 2). Soil 
moisture  content  in  the  depth 20-40 cm de- 
creases gradually to reach a constant level for 
the rest of the  dry season in february (Fig. 2 ) .  
With the exception of a rapid rise in moisture 
content in the upper depth during the month 
of july  (period c,orresponding  wit,h the  first  rain) 
moisture content of the lower depth is always 
higher  than  that of the  upper 20 cm. 
Moisture content of this soil at permanent 
wilting point is 2.3%, a value far superior to  
any  moisture  content  measured  in  both  depths, 
during  the  entire  dry  season. 
In the  experiments where drought was induced 
artificially 83.5% of the  nematodes were tightly 
coiled after  t eatment  until  97.7%  relative 
humidity  (Fig.  4 A-C) ; 97% of these  nematodes 
revived  after  48  hours  in a film of water. 
A  bigh  percentage  (89%) of S. cavenessi 
revived after exposure a t  0% rh for one day ; 
after exposure during 30 days a t  0% rh, 88% 
of the  nematodes  survived  (Tab. 2). 
286 
-_  . - .  
t Percent soit moisture content Soi1 temperature I ‘C l O-2Ocm depth (sramslloog dry soill 10cm  depth t 
O temperature O/’- 
-0’ 
O’ 
’ 2’. 
l mini. 1 l tzo 
Percent soi1 moisture content 
20-40cm depth 
tgramsIl00g dry  soit) 
6 :: 
I o  
1975 ’ 
OCt. nov dec. fan. feb. mar. apr. may ïune ïuly 
1976 
Fig. 2. Soil moisture (0-20 cm depth and 20-40 cm 
depth)  and  temperature  (10  cm  depth  and 50 cm depth) 
during the dry season (October 1975-July 1976) a t  
ISRA Experirnent,al Station  (Barnbey). 
Discussion 
Observations  made  during  the  dry  season 
suggest that there was little if any migration 
from the surface 20 cm to the more moist and 
colder (Fig. 2) lower depths. In fact we did not 
observe a significant  increase in size of the 
S. cavenessi population in the depth 20-40 cm 
in  relation t o  a signifcant,decrease  in size of tlie 
population  in  the  depth 0-20 cm. 
The fact that no larvae and eggs ever were 
extracted  during  the  dry  season  makes it most 
unlikely that  reproduction of S. cavenessi 
enabled this nematode to keep its population 
level during this period. Almost al1 individuals 
of al1 stages of S. cavenessi which survive the 
dry season are coiled. It has  been  demonstrated 
that  a coiled habitus  often  is  related  to  an  anhy- 
drobiotic  state of the  nematode (Crowe & 
Madia,  1974 ; Freckman,  Kaplan & Van  Gundy, 
1977 ; Freckman,  1978 ; Demeure,  Freclrman 
Revue Nématol. 3 (‘2): 283-289 (1980) 
. .~ . - _  - .  
Table 2 
Percentage of coiled Scutellonema  cavenessi and  percentage of nematode  revival  after  treatment 
until  97.7%  relative  humidity (rh), after exposure at  0 %  rh for  one day or thirty days 
Coiled Scutellonerna cavenessi (%)  
% nematode  revival  after  treatment  until 97.7% rh 
y0 nematode  revival  after  exposure a t  0 %  rh  for one day 
% nematode  revival  after  exposure at  0 %  rh for one month 
Revue Nématol. 3 ( 2 )  : 283-289 (1980) 287 
Fig. 4. Morphological aspect of Scutellonema cavenessi 
fernale (A) male (B) and  larva (C) dehydrated on 
Millipore filter  as according to Demeure, Freckman 
and  Van  Gundy (1977) technique. 
~ -- - .  - - - . - _  - - .  
& Van Gundy, 1979~1, b ) .  Accepting this point 
of view, S. cu.r~enessi survives during the dry 
season  in an  anhydrobiotic  state. ' 
One may oppose the preceding  statement  by 
pointing t o  the  fact  that al1 nematodes  extracted 
from soil in Our experinlents were exposed t o  a 
hypertonic  solution (1 25 M sugar  solution).  This 
treatment might cause the nematode to coil. 
In  order tao approach  the  atmospheric  condi- 
t,ions existing  in dry  soil,  nematodes were 
exposed t.o 97.7%  relative  humidity.  Nematodes 
responded t o  this treatment by coiling. There- 
fore it seems  very  likely that the coiling of 
nematodes  extracted  from soil Fwas due t o  
drought and not to  the exposure t o  sugar. 
It has  been  demonstrated  for AphelencArrs 
avenue,  Acrobeloides sp., Scutellokema  brachyu- 
r u m ,  that  Goiling is not caused by t'he relative 
humidity of the  air  in  the soil pores but   by  the 
physical forces  exert,ed  on the  nematode by  the 
film of water  around  the soil particles  (Demeure, 
Freckman & Van Gundy, 1979~) .  The effect of 
coiling would be the reduction of the surface 
of the  tegument  exposed  to  an  environment defi- 
cient in  water  (Bird & Buttrose,  1974). It seems 
probable that the same holds for S.  carrenessi 
in drying soil. 
Anhydrobiosis  in S. curtenessi is a  quiescence, 
because it depends on external factors ; it is 
caused by  unfavorable conditions such as the 
begining of the  dry season. As soon  as  conditions 
become favourable (rainy season) the opposite 
takes  place : reactivation. 
. As a consequence of the anhydrobiotic state 
of the  nematode  during which its  metabolic 
activity is slowed down (Keilin, 1959) its food 
reserves  are  not  exhausted (Cooper & Van 
Gundy,  1979).  This  may  be  the  reason  that , 
females 0f.S. cuvenessi stored  during 30 months 
in dry soil are capable of laying eggs without 
feeding  (Demeure, Netsc.her & Quénéhervé, 
1980). 
The  experiments in vitro demonstrate  that 
it is possible to produce anhydrobiotic S. cave- 
nessi on Millipore filters which are capable of 
surviving a t  least thirty days at 0% relative 
humidity. It may be possible to use the Milli- 
pore  t chnique to induce  anhydrobiosis  on 
populations of S.  carrenessi and  maybe  other 
nematodes  for  the  purposes of storing  alive 
nematodes in the laboratory for long periods 
of time. - , - - . . . ~ _ -  ~
288 Revue  Nématol .  3 ( 2 ) :  283-289 (1980) 
Anhydrobiosis in Scutellonema cavenessi 
ACICNOWLEDGMENTS 
The author thanks M. Luc for helpful comments, 
C. Netscher for translating  the  text  into  English  and 
B. Souchaud  and M. Chpiliotoff for technical  assistance. 
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Revue Nématol. 3 ( 2 )  : 283-289 (1980) 289 


Biology of the plant-parasitic nematode Scutellonema cavenessi Sher, 1964 : anhydrobiosis

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