efficacy of essential oil.pdf

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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