Diem, Hoang Gia

Dommergues, Yvon

Germani, Gaetano

Horizon / Pleins textes

\ 
Influence of nematicide fumigation on mycorrhizal infection 
and N2 f ixat ion i n  field-grown groundnut 
by G. GERMANI, H.G. DIEM9 Y.R. DOMMERGUES 
ORSTOM/CNRS, BP 1386 DAICAR, S6négal 
I. Introduction 
=E===t=I,Z 
I n  the  semi-arid conditions which prevai l  i n  psamment s o i l s  of West Africa, 
crop yields  are l imited not only by mter but also by nematode attacks.  These 
pathogens are well known t o  d i r ec t ly  reduce crop yields  by affect ing t h e  plant 
it self, 
But they can also be harmful t o  it by decreasing the  endomycorrhizal in- 
fection of t he  roots  (Fox and Spasoff, 1972; Schenck and Kinloch 1974, Schenck & 
- 3  al. 1975) and, i n  the case of legumes, by reducing nodulation (Hus'sey and Barker, 
1976; Yeates et a l .  1977) and, consequently, I? f ixat ion (Baldwin e t  al.. 1975, 
Germani unpublished). 
infested s o i l s  by some nenmticides (1,2 dibromo-3- ckloropropanc and 193  dichloro- 
propene and re la ted  C hydrocarbons) 
endomycorrhizal infection of cotton roots  (Bird e t  al. 1974). 
li 
2 
Thus it is not surprising t h a t  fumigation of nematode- 
should r e su l t  in a significant increage of 
3 
The a i m  of t h e  present work i s  t o  evaluate t h e  influence of fumigation of 
a nematode-infest ed s o i l  with 1,2-dibromo-3-chloropropane (DBCP simultaneously 
ugon ( 1) endomycorrhizal infection of roots ,  (2)  N2 f ixa t  ion (3) crop y ie lds  of 
3 different  cu l t ivars  of field-grown groundnut i n  order t o  check whether nematicide 
fumigation can simultaneously protect t h e  plant it s e l f  against nematode and improve 
i t s  nitrogen and phosphorus nut r i t ion  by restor ing t h e  symbiosis with endomycorrhizae 
and Rhizobium. 
I 
II. Material and methods 
æ = E = = f = = æ = = = = P = t P I I  
Groundnut cu l t ivars  28-206 (growth-cycle : 120 days) 55-437 (growth cycle : 
90 days) and GH. 119-20 (growth cycle : 120 days) obtained from the I n s t i t u t  
de Recherche Agricole du Sénégal were seeded at  a distance of 15cm i n  rows 6Ocm 
- 2 -  
apart at the  Patar si te,  25km south of t he  "Centre de Recherche Agronomique de 
Bambey" (Agronomic Research Center at Bambey) , central  Senegal, on July 23, 1977. 
Fertilizer (6: 20: 10, N: P205: K20 mixture) was applied on t h e  experimental area 
at the  r a t e  of 150 kg/ha. 
The main experimental design was made of 9 randomized blocks, with 2 t r ea t -  
ments : fumigated and non-fumigated with nematicide and each plot was composed of 
3 r a w s  of groundnut one for each cul t ivar .  
depth of 20cm using a m i g a n t  injector ,  22 days before sowing. 
appkication was 25 1 ha"' of comercial  nematicide (Nemagon) containing 75% 1,2 
dibromo-3-chloropropane . 
Treated plots  were fumigated at a 
The r a t e  of 
The soil was a ty-picd psamment so i l ' o f  central  Senegal (Dior) characterised 
by a very low exchange capacity (Charreau and Nicou 1971) and heavily infested 
with Scutellonema cavenessi. The experimental si te had been previously cult ivated 
with pearl millet according t o  t h e  t rad i t iona l  pearl-millet /peanut rotation system 
i n  use i n  the  region (Chameau 1974) 
The crop was harvested on October 20, 1977 (cv. 55-43"] and November 10, 
1977 (cv. 28-206 and GH. 119-20). 
I n  order% t o  check the  remanents of t he  fumigation e f fec t ,  an auxiliary field 
experiment with 2 treatments (fumigation performed the year before; no fumigation) 
was se t  up close t o  the  first experimental site. 
experiment w i l l  be @ven i n  another paper (Germani., unpublished), most resu l t s  
repojtied here a re  re la ted t o  the  main experiments. 
Since a detailed report of t h i s  
During the  groundnut growth cycle the  r a i n f a l l  vas low (287" for t he  vhole 
season, June-October) but re la t ive ly  w e l l  distributed. Plant material and s o i l  
were sampled twice (16th and 60th day) i n  order t o  estimate endomycorrhizal in- 
fection, N2 (C H ) 
the  number of measuress only 5 samples, ra ther  than 9, were use6 for  each t r ea t -  
ment. But crop yield estimations were based on the  plant harvest of each of the  
9 replicates.  
f ixat ion and nematode numbers. In  order t o  reduce 2 2  
- 3 -  
E s t  ha t  ion of endomycorrhizal infect  ion 
Five root systems per p lo t  were examined. 
Roots were stored i n  formalin-acetic acid-ethanolL' and then t r ea t ed  and 
stained according t o  t h e  method of Ph i l l i p s  and Hayman ('1970) A microscopic 
examination was made wider 250 x magnification on the  t o t a l  length of each lcm 
rook segment. For each root system, 12-15 segments were observed, The extent of 
mycprrhizal infection was expressed RS percentage of microscope fields w i t h  endo- 
mycorrhizal infected. root s. 
E s t  $mat  ion of N, ( C,H,) f i x a t  ion 
The basic procedure for  t h e  measurement of N2 f ixat ion w a s  t h a t  of Pardy 
- e t  al. (1968), with some modifications. 
were placed i n  57Oml serum bo t t l e s  with a rubber stopper. 
5 W  acetylene and 0.4ml propane ( t r ace r  gas) were injected. 
Immediately after harvest ,  root systems 
Through the  stopper, 
Incubations were allowed t o  proceed for 30 min at ambiant temperature 
(ca. 28'C). The incubation atmosphere was sampled using a 1omL Vacutainer tube. 
The'ethylene assay was performed using a hydrogen flame ionization chromatograph 
(Varian aerograph 1200). The s t a in l e s s  s t e e l  column 150 x 0.3cm was packed with 
Spherosyl X OB 075 80-100 mesh + lo$ J!b3POb . The in jec tor ,  column and detector 
temneratures were respectively 105, 40 and 180%. Ne flow 3Oml min-' 5 H2 f l o w  3oml 
min j compressed air  flow 3"l min . -1 -1 
Acetylene reducing a c t i v i t y  per plant (ARA??) w a s  expressed as micromole 
C2Hz reduced per plant per h. 
Crop yields 
Aerial parts and pods were harvested separately i n  order t o  determine 
their weight af'ter drying at  70-80Oc. 
Enumeration of nematodes 
I 
Nematodes were extracted from fresh soil samples by e lu t r i a t ion  (Seinhorst 
1962) and from roots  by m i s t  chambers (Seinhorst, 1950). 
numbers of Scutellonema cavenessi per dm3 so i l  o r  1OOg root (fresh weight). 
- 1/ Formalin ( 13mL), acet ic  acid (5ml) 50% ethanol (200ml) 
Results were expressed as 
- 4 -  
RESULTS AND DISCUSSION 
1. Effect of nematicide upon nematode populations -
Fumigation with 1.2-dibromo-3 chloropropane s ignif icant ly  reduced nematode 
(Scutellanema cavenessi) populations. 
when f”iga%ion was performed i n  the  same year 
men%). 
experiment ) . 
The effect of t h e  treatment was dramatic 
as t ha t  of the crop (main experi- 
Moreover t h i s  effect  was shown t o  l a s t  at l eas t  fo r  two years (auxiliary 
2. Effect of nematic ide uvon endomycorrhizat ion 
wcorrhizal  infection, as  evaluated at the  first sampliag (16th day) wes 
s i p i f i c a n t l y  increased by fumigation fo r  2 cul t ivars  (28-206 and GH 119-29). 
Data presented i n  table 4 suggests intravarietal  differences between the  
3 cul t ivars  since cv. 557437 showed a tendency t o  r e s i s t  endomycorrhizal infection 
when compared t o  other cul t ivars  . 
. Since the  groundnut (~v.28-206 and GH 119-20) roots were heavily infected 
i n  the  fumigated plots as soon as the  16th day, endomycorrhizal infection of some 
cul t ivars  appeared t o  be a precocious process i n  t h e  edaphic and climatic conditions 
occqing  i n  Senegal, provided that no l imiting factor  - such as nematode at tack - 
occurs. Lata sampling (60th day) did not show any significant difference between 
trea-bed and untreated plots.  
endoqycorrhizd. infection. 
Thus, the  nematicide treatment promoted only early 
In  t h e  case of cu l t ivars  28-206 and 55-437, the  effect  of nematicide fumi- 
gation lasted fo r  2 years : endomycorrhizal infection, as determined on t h e  16th 
day of the growth cycle, did not s ignif icant ly  d i f f e r  when fumigation was performed 
e i ther  j u s t  before, o r  one year before the  groundnut crop (Table 4 ) .  
sidual ef fec t  i s  probably related t o  the residual effect  of fumigation on nqmatode 
populations already mentioned. 
Such a re- 
These results support the conclusion of t he  work of Bird e t  a l .  (1974) 
on cotton, t ha t  nematodes might eventually l i m i t  mycorrhizal infection, but t he  
related mechanism is sti l l  unknown. 
- 5 -  
Microscopical observations showed the t  only very few vesicles  and arbus- 
cules were found i n  roots  of groundnut i n  accordance with t h e  report  of Soss and 
Hvper ( 1973). 
3. Effect of nematicide upon N2 (C2H2) f ixat ion 
Tables 1 2 and 3 show t h a t  no significant .effect  on N2 f ixat ion could be 
detected a t  both sampling dates : 16th day and 60th day. 
However, t i m e  course curves of Acetylene Reducing Activity per plqnt (ARAI'), 
t o  be published elsewhere (Germani, personal communication) 
of cv. 55-437 and GH 119-20 i n  flunigated p lo ts  was markedly higher than t h a t  occuring 
i n  non-Wiigated p lo ts  when plants  were 40-50 days o l d ,  but t h a t  such a difference 
did not show up when plants  were e i the r  16 or  60 days old (Germani unpublished). 
Thus, nematicide fumigation appeared t o  improve ARM? of cu l t i va r s  55-437 and 
GH 119-20 but not t h a t  of cv. 28-206. It i s  surprising t o  note that  whereas 
endomycorrhization of cv. 28-206 was not improved by fumigation, i t s  ARAP was 
grea t ly  enhanced by t h i s  treatment, at  l e a s t  during t h e  period ranging from 
d4y 40 t o  50 when AFW is  known t o  be the  highest. 
indicate t h a t  A M  
4. Effect of nematicide upon crop y i e l d s  
The ef fec t  on crop yields  expressed on a dry weight basis (Table 1 2, 3 )  
was dramatic, confirming previous experimental results already obtfiined by 
(kp?"i (unpublished) i n  Upper Volta and Senegal. 
Analyses of nitrogen and phosphorus of t he  plant material of t h e  present 
eyperiment a re  under way. 
ments performed i n  Upper Volta which indicated t h a t  nematicide fumigation increased 
crop phosphorus content 
might hprove t he  crop phosphorus uptake. 
They a r e  aimed at  checking the  results of f i e l d  experi- 
suggesting t h a t  res torat ion of endomycorrhizal infection 
I n  conclusion, by a l t e r ing  the  physiology OS groundnut, Scutellonema cavenessi 
presumably impedes t h e  establishment and functioning of t he  double plant symbiosis 
( a s s e  e t  al-. 1976, Daft and El-Giahmi 1976) ( 1 )  with endomycorrhizae (2 )  wi th  
- 6 -  
Rhizobium, thus ind i rec t ly  reducing plant phosphorus uptake on t h e  one hand, and 
possibly its water uptake (Saf i r  I__ e t  a l .  1971) and on the other hand, i t s  Ne fixing 
ab i l i t y .  Such consequences are presumably most harmful t o  t h e  plant especially 
in,phosphorus and nitrogen def ic ient  soils which a r e  largely found i n  semi-arid 
West Africa. 
TABLE 1 
Effect of s o i l  fumigation with nematicide on nematorle population, 
N2 f ixat ion,  endomycorrhizal root infection and y ie lds  of f i e l d -  
, 
grown groundnut cv. 28-206 
1 1 Nemat ic ide (Nemgon I 
1 1 No application ! Application I 
I 1 I 
! 1 
I 1 I 
(25 1 ha-’) l ---. ____ I 
1 Early sampline; (16th day) 1 I I 
! i  1 ! I 
I Number of  nematodes s o i l  I 828 ! o * i f  1 
1 
1 1 
! A R A  1 4326 I 12007 N S ! 
1 
! ! $ mycorrhizal roots  I 
1 1 ! 1 
o * * *  ! I 
! 59.6 * * 1 
1450 1 I 
1 
1 
Number of nematodes 10-2g m o t  
22.8 
1 
! Late sampling (60th day) I !  
I 
1 
! 
! 
! 
ao Z R X  I 3892 ! 
! Nupber of nematodes 10’-2g root 1 15688 I 4 * * *  1 
9706 ! . 5498 N S ! 
1 Number of nematodes s o i l  1 
ARA 
! 
I .  
1 
! 
1 % mycorrhizal roots  
! 
I :  
! Crqp yield (harvest)  
1’  : 
1 Pods (d.w.) kg ha-’ 
I 63.6 I 40.7 r$ s ! 
1 ! 1 
I 1 
1 1 ! 
1 1 1 
! 666 ! 1592 * * * ! 
I 
1 2587 i k * 1 1253 ! 1 Aerial par t s  (d.w.) kg ha-’ 1 :  
! Sebd N kg ha-’ 1 24.46 1 58.55 * * I 
ARA : acetylene reducing a c t i v i t y  expressed as nanomoles C2H2 reduced 
* : Significantly different  (P = .01) 
a : Significantly different  (P = .02) 
NS : Not s ignif icant ly  d i f fe ren t  (P = .lo) 
per plant per h 
- 7 -  
TABLE 2 
Effect of s o i l  fumigation with nematicide on nematode population, 
N2 f ixat ion,  endomycorrhizal root infection and y ie lds  of f ie ld-  
grown groundnut cv. 55-43' 
* * I 1 
1 No application ! Appl i c a t  ion 1 _. 
1 
I (25 m ha-' ) 
Y ! 
1 I 
1 
1 
1 
1 
I 
I 
!Early sampling ( 16th day) 
1 
!Number of nematodes dme3 soil 
'Number of nematodes root ! 
JARA 
'$ mycorrhizal roots  1 
! 
'Late sampling (60th dax) I :  
INmper of nematodes dm -3 s o i l  
1 
!ARA 
I% mycorrhizal roots  1 
I 
'Cro yield 
1Pods (d.w.) kg ha '  
'Aerial par t s  (d.w,) 1 .  
!See4 N ke; ha 
f r  
'"$er of nematodes 10 -2 g root 
1 P  
-1 
I 
! 
1 
I 
1 
1 
1 
1 
1 
I 
1 
1 
I 
I 
I 
1 
I 
1 
1 
I 
1 
1 
1 
! 
! 
1 
848 
688 
6220 
28.4 
2148 
33362 
394 1 
54.0 
667 
i 162 
28.92 
1 
! 
! 
1 
! 
1 
! 
! 
! 
! 
! 
! 
1 
1 
! 
! 
! 
! 
I 
! 
! 
1 
1 
! 
! 
1 
O 
O 
9800 
33.0 
16 
O 
7 176 
56.2 
1606 
4400 
64.21 
* X I  
* * %  
N 6  
N S  
*i 
* * *  
N S  
Ia s 
**i 
* * *  
* * *  
I I 
I 
I 
1 
! 
I 
I 
1 
I 
I 
1 
1 
I 
1 
! 
I 
! 
I 
I 
1 
1 
! 
1 
1 
! 
1 
! 
r 
For explanation of abbreviations see Table 1 
n 
' . '  
< 
- 8 -  
c 
- TABLE 3 
Effect of s o i l  m i g a t i o n  w i t h  nematicide on nematode population, 
N f ixat ion,  endomycorrhizal root infection and yields  of f ie ld-  2 
grown groundnut CV. GH 119-20 
! 1 Nemat xc I d e  ( Nemagon I I 
! Application 1 
! 
I 
! 1 1 1 ! (25 1 ha- ' ) I I ! 
I I ! I 
I I I ! 
I l I ! 
1 'Number of nematodes low2 root I 
NO application 
l 
!Early sampling ( 16th day) I I ! 
!Number of nematodes dm-3 s o i l  1 968 I o * * *  I 
o * R R  I 
- IARA I 4908 ! 12082 N S 1 
! 
! 
1 
I 
! I 
! 
! 
1 ! 
1 ! I I 
! I 1 
I ! I 'Late sampling (60th dax) ! 
I ! 
1 
I 
I 'Number of nematodes soil ! 
! 
! 
I 
1 
1760 
76.5 * R * 53 b 8  mycorrhiza3 roots 
4 R R R :  2704 
!Number of nematodes root 1 26058 ! o * * *  1 
1 
1 6665 3~ s 598 1 
!% myF0rrhiza.l roots 
! 
! 
I Crop' y ie ld  
1 
!Pods: (d.w.) kg ha-' 
I 57.4 
I 
1 
! 
I 
1 774 
! 57.0 NS ! 
! ! 
! ! 
! I 
! I 
1 1748 k x k I 
! 4079 * X * 1 
!Seed. N kg ha-' ! 29.84 ! 68.70 1 
! 1879 
I 
! 
'Aerial parts (d.w.) kg ha-' I 
I ! ! I 
For explanation of abbreviations see Table 1 
t 
I I 
I 
- 2 J - f  
.- Aes5dual d f  ect of nemat icicle -rUmigat ion on mycorrhizal infect  ion 
of field-grown groundnut expressed as percentage of infected roots 
determined on 16th day. 
Groundnut 
cu l t ivar  
_-, - 
! -! Fumiaation (20 1 .ha-') ' ' . 
! Just before ! One year before 1 
no fumigation i - - 
(control)  ! groundnut ! &romanut ! I 
! crop ! crop ? 
! ! ! 
! 59.6 b 1 79.8 b I 
! ! 1 
53.8 3 
! ! ! ! 
62.4 bc ! 
1 I 
1 ! 
I ! 
28 - 206 ! 22.8 a 
28.4 a ! ! 
I 
! 33.0 a 
! 
I 
I 
! 55 - 437 
! 
I 
I 
! GH 179 - 20 I 53.8 &c ! 76.5 b I 
! ! ! 1 
! ! 
I 
! --! 1 
Numbers i n  a row not having the  same le t te r  differ 
Multiple Range T e s t .  
P = .O1 by Legay et  al. ( 19.56). 
I' . -  
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Influence of nematicide fumigation on mycorrhizal infection and N2 fixation in field-grown groundnut

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