efficacy of essential oil.pdf
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7/26/2019 Efficacy of Essential Oil.pdf
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Efficacy of essential oils ofCaesulia axillarisand Mentha
arensisagainst some storage pests causing biodeterioration of
food commodities
Jaya Varma, N.K. Dubey )
Department of Botany, Banaras Hindu Uniersity, Varanasi, India
Abstract
The essential oils of Caesulia axillaris and Mentha arensis have been tested for their fumigant activity in the
management of biodeterioration of stored wheat samples by Aspergillus flaus and the insect pests, Sitophilus oryzae and
Tribolium castaneum, at 1300 and 600 ppm, respectively. The findings indicate the efficacy of the oils as potent fumigants
for management of the biodeterioration of stored wheat samples. The oils also controlled the blue mould rot of oranges
caused by Penicillium italicum and enhanced the market life of the oranges for a considerable period, showing their efficacy
as postharvest fungicides of higher plant origin. q 2001 Elsevier Science B.V. All rights reserved.
1. Introduction
The invasion of various food commodities by
fungi and insects causes considerable losses in tropi-
cal and subtropical countries. The use of synthetic
chemicals as pesticides and fumigants has made a
great contribution in the management of such losses
but has also raised a number of ecological and
medical problems due to residual toxicity, carcino- .genicity and teratogenicity Bajaj and Ghosh, 1975 .
At present, only two fumigants are in common use:
methyl bromide and phosphine. Methyl bromide has
been identified as a major contributor to ozone de-pletion, which casts a doubt on its future use in pest
control. There have been repeated indications that
certain insects have developed resistance to phos-
phine, so its use is now suspect. During recent years,
)
Corresponding author. Fax: q91-542-368174.
.E-mail address: [email protected] N.K. Dubey .
some pesticidal plants, e.g. Azadirachta indica,
Chrysanthemum cinerariaefolium and Carum cari
have been receiving global attention and their sec-
ondary metabolites have been formulated as botani-cal pesticides in plant protection Varma and Dubey,
.1999 . Biologicals, because of their natural origin,
are biodegradable and they do not leave toxic residues
or byproducts to contaminate the environment. Some
plant species have a thousand years of history behind
them as aids in the treatment of human diseases, and
oral nontoxicity, at least, is proven. During the
screening of some essential oils under in vitro condi- .tions Varma, 1999 , the essential oils of Caesulia
axillaris have been found to possess strong insectici-
dal activity against the storage insects, Sitophilus
oryzaeand Tribolium castaneum. In the present work,
the in vivo efficacy of the Caesuliaand Mentha oils
have been tested as fumigants of higher plant origin
in the management of biodeterioration of stored wheat
samples, using Aspergillus flaus as a test fungus.
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The efficacy of the oils has also been determined in
enhancing the market life of oranges.
2. Materials and methods
To test the practical applicability of Caesulia and
Mentha oils as fumigants for the protection of stored
food samples from biodeterioration, the experiments
were designed to fumigate the wheat samples sepa-
rately with the vapours of the oils by the method . .adopted by Dubey et al. 1983 , Dikshit et al. 1983
.and Shaaya et al. 1997 . The fumigation of wheat
samples with the oils was done separately in differ- .ent sets. In one set uninoculated treatment , 1.3 and
0.6 ml of the Caesulia and Mentha oils were intro- .duced separately in closed plastic containers 1 l ,
containing 500 gm of wheat samples moisture con-.tent between 11% and 13% by soaking in a piece of
cotton so as to procure concentrations of 1300 and .600 p pm vrv , respectively. Each container was
.made airtight. In another set inoculated treatment ,
the wheat samples, prior to treatment with the oils,
were inoculated with a standard spore suspension of
A. flaus. After 3 days of inoculation, the samples,
similar to the first set, were separately treated by the
Caesulia and Mentha oils.
The control set also contained two setstheuninoculated control and the inoculated control. In
the uninoculated control set, the wheat samples were
stored as such in 1-l plastic containers. In the inocu-
lated control, the wheat sample was inoculated with
a spore suspension of A. flaus and stored similarly.
The inoculation of wheat seeds was done by
preparing a standard spore suspension of A. flaus.
The fungal spores were harvested from a 7-day-old
culture and suspended in 100 ml of distilled water .containing a wetting agent 0.05% Tween-80 by
stirring at high speed in a Waring blender. The
suspension was diluted to obtain approximately 10 4
spores, as counted by a haemocytometer. The seeds
were dipped in the normal spore suspension for 10
min and then dried in an electric oven at 458C for 12
h. The moisture content of the dried wheat samples
of different lots were found to be 11 13%. Three
replicates were taken for each individual set.
After 12 months of storage at laboratory condi- .tions temperature 10468C and RH 3090% , sam-
ples of both treatment and control sets were analysed
for fungi using the agar plate technique of Muskett
. .1948 and the blotter technique of De Tempe 1953 .and Neergaard 1977 . The isolates were then exam-ined and identified Funder, 1968; Moore and Ja-
.ciow, 1979 .
After the analysis of fungi associated with wheat
samples of treatment and control sets, the percent
occurrence of each fungus among the samples anal-
ysed and the percent protection of wheat samples in
the uninoculated and inoculated treatments were ob-
served by following formula.
Percent occurrenceof fungus
No. of coloniesof the fungus
s Total no. of coloniesof all the fungal species
=100
Percent protection of wheatsamples
D yDc ts =100
Dc
Where, D s percent occurrence of total fungi incwheat samples of control sets and D s percent oc-tcurrence of total fungi of wheat samples in treatment
sets.
To determine the efficacy of Caesulia and Men-
tha oils in protecting wheat samples from the storageinsect pests, S. oryzae and T. castaneum, 500-g
wheat samples were prepared as described above.The insectsT. castaneumand S. oryzae 20 adults of
.each insect were then introduced, Caesulia and
Mentha oils were introduced at concentrations of
1300 and 600 ppm, as described above. Control sets
contained wheat samples infested by insects without
any treatment with the oils. After 12 months ofstorage at laboratory conditions temperature 7458C
.and RH 3090% , the analysis of insects associated
with wheat samples of treated and control sets were
made and data recorded.
To determine the potency of the oils in the control
of blue mould rot of oranges caused by Penicillium
italicum, the oranges were treated separately with the
Caesulia axillaris and Mentha arensis oils by the .technique followed by Chandra 1984 and Sharma
.and Yadav 1996 . Mature healthy orange fruits of
medium size were used for the experiment. The fresh
oranges for both treatments and controls were washed
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in running water, surface sterilised with 0.1% sodium
hypochlorite solution for 23 min and then washed
with distilled water. The pathogenicity of the fungus .was tested following Garcha and Singh 1980 . The
fresh oranges were inoculated with P. italicum.
Within 45 days, the oranges showed rotting due to
the characteristic growth of P. italicum.
A syringe was used to produce a 5-mm diameter
injury on the outer surface of the oranges. The
oranges were then inoculated with 10 ml of the
standard spore suspension of P. italicum. The inocu-lated oranges were kept in desiccators four fruits per
.desiccator . The requisite amount of Caesulia and
Mentha oils were introduced separately in the desic-
cator by soaking in cotton pieces, so as to produce
.concentrations of 1500 and 1000 ppm vrv , respec-
tively. The initiation of rotting in the oranges was
observed. Three replicates were kept for treatment
and control sets.
3. Results
3.1. Wheat samples
A total of nine fungi were observed on wheat
samples in the uninoculated control. A. flaus was
found to be the dominant fungus followed by A.niger and A. fumigatus. The treatment of wheat
samples with the Caesulia oil checked the appear-
ance of all the fungi found in the uninoculated
controls. In inoculated samples, only six fungi were
Table 1
Mycoflora of wheat samples treated with Caesulia oil after 12
months of storage
Fungi isolated Percent occurrence of fungi
Uninoculated sets Inoculated sets
Control Treatment Control Treatment
A. flaus 45 0 80 5A. niger 15 0 2 0
A. fumigatus 12 0 2 0
A. sulphureus 2 0 2 0
Rhizopus spp. 10 0 7 0
Mucor spp. 10 0 6 0
Curulariaspp. 1 0 0
P. oxalicum 2 0 0
Absidiaspp. 1 0 0
Table 2
Mycoflora of wheat samples treated with Mentha oil after 12
months of storage
Fungi isolated Percent occurrence of fungi
Uninoculated sets Inoculated sets
Control Treatment Control Treatment
A. flaus 59 0 75 4
A. niger 4 0 3 0
A. fumigatus 2 0 3 0
Rhizopus spp. 15 0 6 0
Mucor spp. 10 0 6 0
Curulariaspp. 4 0 4 0
P. oxalicum 6 0 3 0
isolated. The oil completely checked the appearance
of all of the fungi except A. flaus, found in 5% of
treatments. The result shows that there was 100%
protection of wheat samples from storage fungi in
the uninoculated sets, with 95% protection in inocu- .lated sets Table 1 .
The Mentha oil-treated wheat samples showed
the presence of seven fungi in the control. A. flaus
was found to be the dominant fungus, followed by
Rhizopus and Mucor species. The Mentha oil
checked the appearance of all the fungi appearing in
uninoculated sets. In the case of inoculated controls,
seven fungi were isolated. The oil completely
checked the appearance of all the fungi except for A.flaus, which occurred in 4% of treatments. The
results indicate that there was 100% protection of
wheat samples from storage fungi in uninoculatedsets, with 96% protection in inoculated sets Table
.2 .
The insects, S. oryzae and T. castaneum were
isolated from the wheat samples in control sets. The
presence of both the insects was completely checked
in the wheat samples treated with Caesulia and .Mentha oils Table 3 .
Table 3Presence or absence of insects on wheat samples after 12 months
of storage
. .q denotes presence of insects, y denotes absence of insects.
Insects isolated Control Treatment
Caesulia oil Mentha oil
Sitophilus oryzae q y y
Tribolium castaneum q y y
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Table 4
Effect of Caesulia an d Mentha oils on decay and storage life of
oranges infected with P. italica
Orange fruit Initiation of rotting Enhancement of
. .of fruit days storage life days
Control 3
Caesulia oil 6 3
Menthaoil 10 7
3.2. Oranges
The Caesulia oil-treated oranges showed an in-
creased storage life of 3 days, and the Mentha
oil-treated oranges showed an increase of 7 days. No
visual symptoms of possible injury caused by the .oils were observed on the peel of the fruits Table 4 .
4. Discussion
Although, during in vitro experiments, the Caesu-
lia and Mentha oils have been reported to inhibit
fungi at minimum inhibitory concentrations of 1300 .and 600 ppm, respectively Varma, 1999 , the in
vivo potency of the oils as fumigants is being re-
ported for the first time. Since, at these concentra-
tions, the fungitoxic nature of the oils was apparently
due to their vapour toxicity, therefore, in vivo fumi-
gant activity was also tested at these concentrations.
However, the efficacy of the oils in the control of
rotting in oranges was tested at higher concentrations .1500 and 1000 ppm because of the possibility of
adsorption of oil by the oranges. The oils were able
to control both fungi and insects, in the management
of biodeterioration of wheat samples from fungal, as
well as insect pests. This dual toxicity is lacking
from most synthetic chemicals. After a large-scale
trial, the oils may be recommended as substitutes for
synthetic fumigants. Unlike the prevalent fumigants,
the problem due to the development of resistantstrains of fungi and insects may be solved by the use
of essential oils as fumigants in the management of
stored insect pests because of the synergism between
the different components of the oils. The nonmam-
malian toxic nature of the oils have already been .tested by the author Tiwari et al., 1998 . Therefore,
the findings of the present study indicate the possi-
bility of exploitation of the essential oils of C.
axillaris and M. ar
ensis as fumigants of higherplant origin for their safe use in the protection of
stored food commodities from biodeterioration.
However, further studies on large-scale trials are
required to find out the minimum dose of the oils
with respects to storage containers for their action as
fumigants.
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