AllelopathyJournal 7 (2): 285-258 (2000)
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SHORTCOMMUNICATION
Exogenoussalicylic acid reduces Meloidogyne incognita
infestationof tomato
B. NANDI, N. C. SUKUL and S. p. SINHA BABUDepartmentofZoology
visva-Bharatiuniversity, santiniketan- 73123s, west Bengal, India
(Received in revised form : April 25,lg99)
Key words : Allelochemical, Meloidogtne incognita, resistance,salicylic acid, tomato
INTRODUCTION
Chemical nematicides cause environmental pollution (5), contaminate ground
water(6) and leave undesirableresiduesin edible parts of plants (8, 13). Plants have
manydefencemechanismsagainstthe pathogensattack. When plants recognisethat they
arebeinginvadedby a pathogen,a number of responsesmay be induced surroundingthe
infectionsite. In addition, uninfected parts of the plant develop greater resistanceto
furtherinfections by pathogens and this is called systemic acquired resistance(SAR)
(10,11).SAR can be inducedby allelochemicalssuch as salicylic acid (SA) producedby
manyplant spp. and its derivatives. The involvement of SA in plant defence was first
reported
by White (14), who observedthat injection of aspirin or SA into tobacco leaves
enhanced
resistanceto subsequentinfection by tobacco mosaic virus (TMV). This
treatment
also induced pathogenesisrelated (PR) proteins accumulation(l) and acquired
resistance
against many other pathogens, like virus, bacteria and fungus in numerous
plants(9). In tobacco after TMV infection, SA accumulatedat high levels in the infected
partandthis increaseparalled the transcriptionalactivation of PR genesin both inoculated
anduninoculatedleaves.ExogenousSA also induced the transcriptionof same set of
genes
that are activatedsystemicallyafter TMV infection (3). We had studiedthe effect of
someinducerson expressionof pathogenesisrelatedgenesin gardenplants infected with
M e l o i d o g t neinc ognit
a a s a p a rto f b i g s tu d y o n i n d u cti onof S A R i npl antsagai nst
( 12)
root-knot
disease.The aim of presentstudy was to seewhetherexogenousSA reducesM
incognita
infestationof tomato plant and augmentsplant growth.
'CorresDondence
author
Nandi et al
286
MATERIALS AND METHODS
In vitro test
Salicylic acid (SA), obtainedfrom Sigma CommercialCo., USA was dissolved in
sterile distilled water at a concentration of 4 mg/ml. Active M. incognita juveniles
(J-2), obtained by sieving infected soil of garden microplots grown with tomato
(Lycopersicon lycopersicum) plants were kept in sterile tap water in cavity blocks, each
containing 100 t l0 J2. Water was pipetted out and immediately replacedby 5 ml of the
test solution. One cavity block containing sterile tap water served as the control.
Observationwas made at room temperature (27 t2o C) every hour for 6 h.
Phytotoxicity test
Salicylic acid (SA) was dissolved in a potassium-phosphatebuffer (pH 6) and
sprayed on l0 tomato plants at 6-leaf stage at the concentrationof l0 mM. The plants
grown in pots, were sprayed in such a manner that the aerial parts were fully drenched.
Pot test
Aseptically germinatedseedsof tomato Pusa Ruby, were sown @ one seed/ pot
(32 cm dia.) containing a mixture of clay soil and compostedmanure (2 : I w/w), which
was treatedpreviously with boiling water. The total weight of the soil and manure in each
pot was 4.5 kg. Each treatment group consisted of l0 pots. The groups were :
uninoculated untreated,inoculated untreated,SA-pretreatedinoculated. When the plants
were at 6-leaf stage, inoculated untreated group and the SA-pretreated group were
inoculated with M. incognita juveniles@ 4000 + s[2juveniles/plant. SA was dissolved in
potassium-phosphate
buffer (pH 6) and applied by foliar spray at the concentrationof l0
mM, 24 h before the infection. Inoculated untreatedand uninoculated unffeated plants
were sprayedwith distilled water. The experimentswere conductedoutdoors at ambient
atmospherictemperature 23t50C and humidify 8515%. All the plants were uprooted 53
days after inoculation and their shoot lengths,shoot weights, root lengthsand root weights
were measured. The root galls on each plant were counted and the nematodepopulation
in2groot and 2009 soil was estimatedby the modified Baermanmethod. Three samples
of roots from each group of plants were taken at random and the total protein content in
each sample was estimated by the Folin-phenol method (7). Data were analysed by
ANOVA.
RBSULTS AND DISCUSSION
In vitro test
No mortality of nematodeswas recordedupto 6 h.
287
Salicylic acid as nematicide
Phytotoxicity
test
Initially, application of SA to the leaves induced necrotic lesions, which
disappeared
12 days after treaffnerlt. The treated plants did not show any toxic effect in
theformof wilting and yellowing of leavesin the next l5 days.
Pottest
SA increased plant growth in terms of shoot length, shoot weight and root length
ascompared
to the inoculateduntreatedplants (Table l). Root galls, nematodepopulation
in rootandsoil and root protein content were significantly reduced in SA treated plants as
compared
to the unffeated ones (Table l). Pre-treatment with SA showed better plant
gowth and lesser intensity of root-knot disease as compared to the post-inoculation
(unpublisheddata).
freafinent
TableL Effectof salicylic acid on the growth of tomato, root galling, nematodepopulation in root and soil and
proteincontentof root (Mean of l0 replicateswith S.E.)
Treatment
Shoot
Length
(cm)
Uninoculated 68.2a
13.04
Inoculated
67.4a
!3.46
SA-pretreated 82.8b
+1.93
Shoot
Weight
(e)
Root
Length
(cm)
67.8a
r8.0
73.4a
!43
l26b
t7.17
27.3a
tt.37
25.4a
t2.54
32.3b
+1.49
Root
Weight
RootY
gall No.
J2/2g
root
J2/200 g
soil
(me/e)
(e)
12.9a
11.03
23.0b
X2.42
16.3a
!1.73
Root
protein
0
0
0
3255a
1608.2
1029b
!248.6
1267a
r105.3
397b
!117.7
1507a
1166
588b
!117.4
2.15a
10.02
3.3b
+0.07
2.5c
+0.05
(p=0.05)
Means
carrying
same
letters
in a column
arenotsignificantly
by analysis
of variance.
different
YTomato
plants
inoculated
larvae(4Q00t542/pot)
andharvested
53daysafter
at6 leafstagewithM. incognita
inoculation.
Evidently,SA could significantly ameliorateroot'knot diseaseand improve plant
growth.SA applied on the leaves at low dose could induce some resistancein tomato
lo M. incognita infection. Root invasion by cyst nematodes produced systemic
accumulation
of new pathogenesisrelated (PR) proteins in the leavesof potato plants (2).
Application
of SA or its analogueaspirin inducesrapid expressionof pathogenesisrelated
genes
(4). It appearsthat SA might have induced synthesisof PR proteins in the treated
plantswhichin turn reducednematodeinfestation.Thus SA could serye as a prophylactic
forthecontrolof nematodeinfection.
ACKNOWLEDGBMBNTS
Theauthorsthank th€ CSIR, New Delhi, India for financial support.
288
Nandi et al
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