Diem, Hoang Gia

Dommergues, Yvon

Germani, Gaetano

Horizon / Pleins textes

Influence of 1,2 dibromo-3-chloropropane  fumigation 
on nematode population,  mycorrhizal  infection, N, fixation 
and yield  of  field-grown groundnut 
Gaetano  GERMANI*, Hoang Gia DIEM** and Yvon R. DORIIMERGUES** 
* L a b o r a t o i r e   d e   N h a f o l o g i e  et * *  Laboratoire de Microbiologie des Sols, 
O R S T O M ,  B.P. 1386, Dakar,   Sénégal .  
SUMMARY 
DBCP fumigation of a typical  sandy soil of Central Senegal (Dior soil) on which groundnut  is commonly culti- 
vated  significantly reduced the size of Scutellonema  cavenessi  populations,  favoured  early  infection  by endomycor- 
rhizae  in  two of the  three  groundnut  cultivars  studied, increased nodulation  and  nitrogen  fixation  (measured  by the 
acetylene  essay),  and  dramatically increased crop yields. From  these  results, it is concluded that S.  cavenessi does 
alter the physiology of the groundnut plant, by affecting the establishment and Iunctioning of the symbioses 
between the  plant  and  both endomycorrhizae and Rhizob ium.  Thus,  parasitism  by  this  nematode  reduces  the  talie-up 
of phosphorus  by  the  plant as well as its  ability  to fix nitrogen. 
. R ~ S U M ~  
Influence d’un traiternent nématicide avec le 1 ,2  dibro1no-3-chloropropane sur les populations de nématodes,  
l ’ infect ion  mytorhiz ienne,   la   f ixat ion  de N ,  et les rendements  de  l’arachide 
Le traitement  nématicide  d’un sol Dior typique  du  Centre Sénégal cultivé en arachide au moyen  du DBCP réduit 
significativement les populations de Scutellonema cavenessi;  améliore, chez deux sur trois des cultivars utilisés, 
,l’infection endomycorhizienne précoce ; accroît la fixation de l’azote mesurée par la méthode de l’acétylène ; 
accroît de  façon spectaculaire les rendements de l’arachide. On déduit de ces résultats  qu’en  altérant la physiologie 
de l’arachide, S. caueizessi handicaperait I’établissement et  le fonctionnement de la  double symbiose qui s’établit 
entre la plante, les endomycorhizes et les R h i z o b i u m ,  réduisant ainsi d’une part l’absorption du phosphore e l  
d’autre  part son aptitude a fixer l’azote atmosphérique 
In semi-arid conditions which prevail  in  West 
Africa, crop yields  on sandy soils are  limited not 
only by  water  but also nematode  attacks. 
Not only do nematodes reduce crop yields by 
direct effect but also by  interactions  with  other 
organisms.  Nematodes may decrease endomy- 
corrhizal  infection of roots (Fox & Spasoff, 1972; 
Schenck & Kinloch 1974, Schenck, Kinloch & 
DiclCson, 1975)  and, in the case of legumes, 
reduce nodulation  (Hussey & Barker, 1976 ; 
Yeates et al., 1977) and, consequently, N ,  fix- 
ation  (Baldwin,  Barker & Nelson, 1975 ; Germani, 
1979).  Thus, i t  is not  surprising that fumigation 
of nematode-infested soils by some nematicides 
as DBCP (1,2 dibromo-3-chloropropane) or 1,3 
R e v u e  Nérnatol. 3 (1) : 75-79 (1980) 
dichloropropene resultecl in a significant  increase 
of endomycorrhizal  infection of Cotton roots 
(Bird, Rich & Glover, 1974). 
The  aim of the  present worlc was t o  evaluate 
the influence of fumigation of a  nematode- 
infested soil with . DBCP upon (i) endomy- 
corrhizal  infection of roots, (î î)  N,  fixation, 
( î i î )  crop yields of three different cultivars of 
field-grown groundnut  in  order  to  determine 
whether soil fumigation  can kill parasitic 
nematodes  and also improve  nitrogen  and 
phosphorus nutrition of the  plant  by restoring 
symbiosis with endomycorrhizal  fungi and 
R h i z o b i u m  spp. 
75 
G. Germani, Hoang Gia Dietn R- Y.R. Dommergues 
L 
Material and methods 
The  experimental  rea was located near 
Patar, 25  km South of the (( Centre de Recherche 
Agronomique de Banlbey )) (Agronomic Research 
Center at  Bambey), Central Senegal. 
The soil was a typical sandy soil of Central 
Senegal (vernacular name : Dior) characterized 
by a  very low cation'  exchange  capacity  (Char- 
reau & Nicou, 1971) and heavily infested with 
Scutellonerna cavenessi Sher, 1963. The experi- 
mental  site  had been previously cultivated 
with pearl-millet, (Pennisetzzrn typhoides Burns, 
Stapf & Hubb.)  according'  to  the  traditional 
pearl-millet/groundnut rotation system in use 
in the region (Charreau,  1974). 
Fertilizer (6 : 20 : 10, N : Pz05 : K,O mixture-) 
was applied on the experimental area at  the 
rate of 150 kg  per  ha. 
The  experimental design consisted of nine 
randomized  blocks,  with  two treatments : fumi- 
gated  with DBCP in 1977 (14 days before plant- 
ing)  and  non  fumigated.  Treated  plots were 
fumigated, a t  a  depth of 20 cm, 14 days before 
sowing a t  a  rate or 25 l /ha of commercial nema- 
ticide,  Nemagon (75 y. 1,2. dibromo-3-chloro- 
propane). 
Groundnut  cultivars 28-206 (growth-cycle : 
120 days), 55-437 (growth cycle : 90 days), 
and GH 119-20 (growth cycle : 120 days), 
obtained from the Institut Sénégalais de Re- 
cherche Agronomique, were planted at  15 cm 
intervals  in rows GO cm apart, on July 23,  1977. 
Each  plot was composed of three rows of groun- 
dnut, one of each cultivar. 
During the groundnut growth cycle rainfall 
was low (287 mm  during  June-October),  but 
well distributed.  Root  systems  and soil were 
sampled twice (16th and 60th day) in order to 
estimate endomycorrhizal infection, N, (C,H,) 
fixation  and  nematode  numbers. Only five 
rather than nine replicates were used for each 
treatment. 
The crop was harvested  on October 20th 
1977 (cv. 55-437) and November 10th 1977 
(cv. 28-206 and GH 119-20). Crop yield estima- 
tions were based on the plant harvest of each 
of the nine  replicates. 
Interpretation of data was performed using 
Mann-Whitney test, (Snedecor & Cochran, 
1967) . .  for acetylene  reducing  activity  per  plant 
76 
(ARAP)  and mycorrhizal infection p'ercentage ; 
classical parametric (( t )) test for other data. 
ESTIMATION OF ENDOMYCORRHIZAL  INFECTION, 
Five root systems per plot were examined. 
Roots were stored  informalin-acetic acid- 
ethanol (1) and then treated'and stained amor- 
ding t o  the method of Phillips and Hayman 
(1970).  A microscopic examination was made 
under 250 magnification on  the  total  length of 
each 1 cm root segment. For  each  root  system, 
12-15 segments were observed. The extent of 
mycorrhizal  infection was expressed  as  percent- 
age of microscope fields with endomycorrhizal 
infected roots. 
ESTIMATION OF N,  (C,H,) FIXATION 
, The basic procedure for the measurement of 
N,  fixation was that of Hardy et al., (1968), 
with some modifications. Immediately  after 
harvest, root systems were placed in 570  ml 
serum bottles with a rubber stopper. Through 
the  stopper, 50 ml acetylene and 0.4 ml  propane 
(tracer gas) were injected.  Bottles  were  incubated 
for 30 mn  at  ambiant  emperature ( c .  280). 
The incubation atmosphere was sampled using 
a  10  ml  Vacutainer tube.  The  ethylene  assay was 
performed  using  a  hydrogen flame ionization 
chromatograph  (Varian  aerograph  1200).  The 
stainless  steel column 150 x 0.3  cm  was  packed 
with Spherosyl X OB 075 80-100 mesh + 10 y. 
Na3P04.  The  injector, column and detector 
temperatures were respectively  105, 40 and 
1800, N, flow 30 ml per minute, H, flow 30 ml 
per minute, compressed air flow- 300 ml per 
minute.  ARAP was expressed as nanomoles 
C,H, reduced  per plant  per  hour. 
CROP YIELDS 
Aerial parts  and pods were harvested  separa- 
tely and their weights determined after drying 
a t  70-800. The  nitrogen  content of plant  tissues 
was determined by Kjeldahl  analysis.  Phospho- 
(1) Formalin (13 ml), acetic acid (5 ml), 50 y0 ethanol 
(200 ml). ' 
Revue  Ne'matol. 3 (1) : 75-79  (1980) 
DBCP, nernutodes,  mycorrhizae, N ,  fixation  and  yield of groundnut 
rus analysis was performed using the molyb- 
dophosphoric blue color method  after  wet 
oxidation of plant tissues by means of the 
HN03-HC104 acid mixture. 
ENUMERATION OF NEMATODES 
Nematodes were extracted from  fresh soil 
samples by  elutriation  (Seinhorst, 1962) and 
from roots by  mist  chambers  (Seinhorst,  1950). 
Results were expressed as numbers of Scutello- 
nernn cavenessi per dm3 of soil or 100 g of roots 
(fresh weight). 
Results and discussion 
EFFECT OF NEMATICIDE UPON NEM,ATODE 
POPULATIONS 
DBCP fumigation significantly reduced Scu- 
tellonelna ca.uenessi populations  (Tab.  2).  The 
effec,t of the  treatment was dramatic when plots 
were fumigated in the same year as the crop 
was grown. 
Table 1 
Effect of DBCP fumigation on mycorrhizal 
infection of field-grown groundnut expressed 1 
as percentage of infected  roots. 
Groundnut  cultivars 
CU.  55-437 C U .  28-206 C U .  GH 119-20  
1 
First sanlpling 
(16th  day) 
No fumigation 28.4 a (a) 22.8 a (a) 53.8 a (b) 
Fumigation 33.0 ab  (a] 59.6 b (b) 76.5 a (b)  
Second  sampling 
(60th  day) 
No fumigation 54.0 bc ( a )  63.6 b (a) 57.0 a (a )  
Fumigation  56.2  c (a) 40.7 ab (a) 57.4 a (a) 
Numbers  in  columns  not  having  same  letter  and  num- 
bers  in rows not  having  same  letter  between  brackets 
differ P = .O5 by Mann-Whitney test (Snedecor & 
Cochran, 1967). 
Revue NPtnatol. 3 (1)  : 75-79 (1980) 
EFFECT OF NEMATICIDE UPON ENDOMYCOR- 
RHIZAL  INFECTION 
Mycorrhizal infection, as measured at   the 
first  sampling  (16th day), was significantly 
higher in  fumigated  plots for two  cultïvars 
(28-206 and  GH 119-20). ' 
Data in Table 1 suggest differences between 
the  three  cultivars since endomycorrhizal infec- 
tion was lower in cv. 55-437 than other  cultivars. 
Since groundnut (cv. 28-206 and GH 119-20) 
roots were heavily  infected in the fumigated 
plots  as  early  as the  lGth  day, endomycorrhizal 
infection of some cultivars appeared to be an 
early process in  the edaphic and  climatic 
conditions of Senegal,  provided that there is 
no  limiting  factor,  such  as  nematode  injury. 
No significant difference between treated  and 
untreated  plots was found at  late sampling 
(60th day). Thus, DBCP treatment stimulated 
an early  endomycorrhizal  infection. 
These results  support  the conclusion of Bird, 
Rich and Glover (1974) that nematodes might 
eventually limit mycorrhizal infection, but  the 
related  mechanism  is  still  unknown. 
Microscopical observations showed that only 
very few vesicles and arbuscules were found  in 
roots of groundnut as reported by Ross and 
Harper (1973). 
EFFECT OF DBCP UPON N,  (,C,H,) FIXATION 
Table 1, shows that no significant effect on 
N,  fixation could be detected  on  either  sampling 
date. 
However, time course curves of acetylene 
reducing activity per plant (ARAP) (Germani, 
unpubl.)  indicate that ARAP of cv. 55-437 and 
GH 119-20 fumigated  plots was markedly 
higher than  that occurring in non-fumigated  plots 
when plants were 40-50 days  old, but  that  such 
a difference was not detected up when plants 
were either 16 or GO days old. 
Thus, DBCP fumigation  appeared to improve 
ARAP of cultivars 55-437 and GH 119-20 but 
not  that of cv. 28-206. I t  is interesting t o  note 
that whereas ARAP of cv. 28-206 was not 
improved by fumigation,  its endomycorrhizal 
infection was greatly enhanced by this treat- 
ment, at least during the period ranging from 
day 40 to 50 when  ARAP of groundnut is 
77 
G. Germani, Hoang Gia Diem & Y.R. Dommergues 
TABLE 2 
Effect of soil fumigation  with DBCP  on nematode  population, N, fixation, 
endomycorrhizal root infection and yields of field-grown groundnut (cv. 55-437 ; 28-206; GH 119-20). 
cv. 55-83? CV. 28-206 cv. GH 119-20 
DBCP Control DBCP Control DBCP Control 
Early sampling (16th  day) 
Number of nematodes (1) O (o.) 848 O (o.) 828 O (o.) 
Number of nematodes (,) 0 (ooe) 688 O (0.0) 1450 
A  R  A  P (3) 9800 (N.S.) 6228  1 .007 (N.S.) 4362  12.082 (N.S.) 
ya mycorrhizal  roots 33.0 (N.S.) 213.4 59.6 (O)  22.8 76.05 (O)  
O (o.) 
Late  sampling  (60th  day) 
Number of nematodes (l) 16 (0.0) 248 80 (o.) 3892 4 (soc) 
Number of nematodes (,) O (0.0) 33362 4 (0.0) 15688 O (oeo) 
A  R  A  P(s) 7176 (N.S.) 3941 5498 (N.S.) 9706 6665 (N.S.) 
ya mycorrhizal root,s 56.2  (N.S.) 54.0 40.7 (N.S.) 63.6 57'.0 (N.S.) 
Crop  yield (kg per,ha) 
Pods (d.w.) 1197 (o.) 497 1893 (0.0) 793 1707 (0.0) 
Aerial parts (d.w.) 3279 (oeo) 866 3071 (0.0) 1485 3975 (o.) 
Seed N 30.20 (0.0) 13.30 44.50 (0.0) 18.90 45.90 (0.0) 
Seed P 3.02 (es.) 1.29 3.56 (0.0) 1.79 4.59 (O..) 
(1) numbers  per  dm3 soil 
(2) numbers per 100 g (d.w.) roots 
(3) ARAP : Acetylene  reducing activity expresscd  as  micromoles C,H, reduccd  per  plant  per  h. 
08. : Significantly  different (P=  .001) 
0 : Significantly different (P= .O5 ) N.S. : Not significantly different (P= 2 .10) 
known t o  be the highest  (Germani,  unpubl.; 
Ducerf , pers.  comm.). 
EFFECT OF NEMATICIDE UPON CROP YIELDS 
DBCP increased crop yields expressed as dry 
weight basis (Tab. 2) confirming  previous  exper- 
imental results (Germani, 1979). 
In conclusion, Scutellonema  cavenessi, presum- 
ably impedes the establishment and function- 
ing of the double plant symbiosis (Mosse, 
Powell & Hayman,  1976;  Daft & El-Giahmi, 
1976) (i) with  endomycorrhizae (ii) with 
Rhizobium, thus indirectly  reducing  plant  phos- 
phorus uptake, and possibly its water uptake 
(Safir,  Boyer & Gerdemann,  1971),  and  also, 
its N ,  fixing ability.  Such consequences are 
968 
1760 
4908 
53.8 
2704 
26058 
5981 
57.4 
746 
1829 
19.70 
1.86 
presumably  most  harmful t o  the plant espe- 
cially in  phosphorus  and  nitrogen deficient soils 
which c.ommonly ocmr  in semiarid West Africa. 
ACRNOWLEDGEMENTS 
The  authors  are  indebted  to D.P. Taylor  for  valuable 
criticism of the. manuscript and to C. Paycheng for 
plant analyses. 
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Revue Nématol.  3 ( 1 )  : '75-79 (1980) 79 


Influence of 1,2 dibromo-3-chloropropane fumigation on nematode population, mycorrhizal infection, N2 fixation and yeld of field-grown groundnut

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