Post-Harvest Deterioration of Cassava and its Control Using Extracts of Azadirachta Indica and Aframomum Melegueta

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ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.e-journals.net 2009, 6(4), 1274-1280



Post-Harvest Deterioration of Cassava and its
Control Using Extracts of Azadirachta Indica
and Aframomum Melegueta


R. N. OKIGBO, RAMESH PUTHETI* and C. T. ACHUSI

Department of Botany,
Nnamdi Azikiwe University Awka, Anambra State, Nigeria.
*Member, An American Association of Pharmaceutical Scientists (AAPS),
236-203, Saint David Court, Maryland, USA.
[email protected]; [email protected]


Received 28 January 2009; Revised 22 April 2009; Accepted 28 April 2009

Abstract: Post-harvest deterioration is the most important cause of loss in
cassava production and this is mainly as a result of microbial invasion of the
tubers. This research was therefore carried out to identify and control the
organisms responsible for post-harvest deterioration of cassava tubers.
Ethanolic and water extractions of Azadirachta indica (A. Juss) leaves and
Aframomum melegueta (Schumann) seeds were used as antifungal agents and
the susceptibility of four of the isolated pathogenic fungi to them was observed
in culture. The tested organisms were Aspergillus niger Van Tiegh,
Botryodiplodia theobromae Pat, Fusarium solani (Mart). Sacc and Penicillium
oxalicum
Currie and Thom. All tested organisms showed different degrees of
inhibitions by the extracts with A. niger being the most inhibited by ethanolic
extraction of A. melegueta. The overall result showed that A. indica was more
active on the organisms though it’s effects and that of A. melegueta were not
significantly different (P>0.05).

Keywords: Cassava, Plant extracts, Fungi, Post harvest deterioration.

Introduction
Cassava (Manihot esculenta Crantz) belongs to the family Euphobiaceae. It is a perennial
woody shrub that is commonly grown as an annual throughout the lowland tropics. Since its
introduction to Africa in the late sixteenth century, cassava had served as a staple food
source for the teeming population of people in this region, and this is a result of its place as
the major source of low-cost carbohydrate. It is the major carbohydrate food for an
estimated 500 million people and in tropical Africa, it is the single most important source of
calories in the diet1.

Post-Harvest Deterioration of Cassava
1275

The rate of post–harvest deterioration in cassava tubers is high and this is as a result of
invasion by microorganism. The following microorganisms had been successfully isolated
from cassava tubers rots: Aspergillus flavus Lark ex Fr., Betryodioplodia theobromae Pat.,
Fusarium solani (Mart). Sacc., Mucor sp., Rhizopus sp, Trichodema harizianum Rifai,
Cylindrium clandestrium Corda and Diplodia manihortis Sacc2-4.

Several studies by the National Resources Institute (NRI) and International Centre
for Tropical Agriculture have led to the development of some storage systems based on
root curing in polyethylene bags and treatment with a thiabendazole–based chemical to
prevent the onset of deterioration5. The curing process involves exposure of the fleshly
harvested tubers to temperatures of 25-35 0C and relative humidity of 80-90 percent for
7-14 days6.

However, farmers in developing countries like Nigeria either cannot afford the cost of
curing materials or they lack the expertise or equipments required to maintain the required
temperature and relative humidity for the needed number of days. As a result of these
restrictions and many more, a lot of natural plant extracts had been tried in the control of
post harvest rot in many root and tuber crops7-9. The advantages of these natural plant
products include local availability, little or no toxicity to humans and simple preparation
procedures10.

Azadirachta Indica A. Juss which belongs to the family Maliacea is an evergreen tree
that is abundantly found in tropical and sub-tropical climates. In Nigeria, it has been used as
a cure for fever, intestinal disorders, skin problems, cough and ulcers. They are used as oral
medicine, cosmetics, tooth powders and even as tooth brushes.

Aframomum melegueta Schumann, a member of the family Zingiberaceae, bears tiny
hot-tasting seeds that are of traditional importance to the people of Eastern Nigeria. It is
used for inflamed conditions of the throat, fevers and exanthemata11. Traditionally, it is
made into powdered form which is subsequently dissolved in hot water for treatment of
common cold and toothaches.

The necessity of anti-microbial agents which are cheap, easier to prepare and that would
be available for the control of post-harvest rot of cassava tubers makes this research a
necessity. The study therefore tries to investigate the effects of extracts from Azadirachta
indica
and Aframomum melegueta on post-harvest tuber rot of cassava.
Objectives of research
(i) To isolate and identify the organisms responsible for the post-harvest deterioration
in cassava.
(ii) To determine the frequency of occurrence for each of the isolated organisms.
(iii) To determine the extent of fungal inhibition by extracts from A. indica and A.
melegueta.
Experimental
Sources of materials
The cassava tubers with signs of rots and healthy cassava tubers were obtained from a local
farm at Awka, Anambra State, Nigeria. The Aframomum melegueta (Schumann) seeds and
Azadirachta indica (A. Juss) leaves were also obtained from bushes around Awka. The
plants were identified by Prof. C.U. Okeke of the Department of Botany, Nnamdi Azikiwe
University, Awka, and samples were kept in the Department.

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RAMESH PUTHETI et al.

Isolation of fungal pathogens
Diseased cassava samples were surface sterilized by cleaning with 70% ethanol solution.
Then with a sterile kitchen knife, it was cut open to reveal the boundary portion between the
rotted and healthy parts. Carefully, portions (about 3 mm in diameter) were taken from the
boundary and inoculated on the solidified SDA medium. The plates were then incubated on
the laboratory bench at room temperature (27±2 0C) for 2-5 days. They were examined daily
for presence of fungal growth. The fungi isolated were put into pure culture and stored in
slants in the refrigerator at 4 0C.
Determination of percentage of fungal occurrence
This was done to determine the frequency of occurrence of the different fungal isolates.
Isolations were made from eight different rotted cassava tubers and were cultured
differently. The number of occurrence for each of the isolates in the eight different samples
were recorded and calculated as a ratio of the total number of occurrence and was then
expressed as a percentage (Table 1). It was given by the formula below;
?
100
Percentage occurrence=
X
N
1
? = Total number of each organism in all the samples.
N = Total number of all the organism in all the samples screened.
Table 1. Percentage frequency of occurrence of fungi on rot cassava.

Isolate
Frequency of occurrence, %

Fusarium solani
15.10
F. oxysporum
2.14

Candida spp
1.73

Aspergillus niger
16.25
A. tamarii
2.42

Mucor spp
6.90

A. flavus
8.92

Penicillium oxalicum
6.80
P. digitatum
1.71

Trichoderma viride
8.62

Neurospora spp
3.45

P. chrysogenum
3.56
Botryodiplodia theobromae
5.17

Geotrichum candidum
6.90
Rhizopus stolonifera
10.34
Identification of isolates
The pure culture isolates obtained from the diseased cassava tubers were used for the
purpose of identification.

Each isolate was subjected to colony and microscopic examinations during which
their structural features were observed. The structures of the growing fungi were first
studied under the hand lens. This was followed by a slide mount of each Isolate under
the lactophenal cotton blue stain. The characteristics observed were matched against
those available in manuals of Barnett and Hunters12. They were then identified
accordingly.

Post-Harvest Deterioration of Cassava
1277
Pathogenicity tests
Each of the fungi isolate obtained from the diseased cassava tubers was tested for its ability
to cause the same disease condition in a healthy cassava tuber.

A healthy cassava tuber was first washed with a sterile water and then surface sterilized by
dipping cotton wool into 70% ethanol solution and then used to clean the surface. With the aid of a
sterile 30 mm diameter cork borer, a cylindrical core was removed from the cassava tuber. A
reconstituted culture of the isolate was then introduced into the open core and the core was replaced
and sealed with sterile petroleum jelly. The tubers were kept at room temperature for ten days.

On establishment of disease condition, inoculums were taken again from the infected
cassava tubers and cultured. The resulting mixed cultures were subcultured and the resulting
pure cultures were characterized and identified as the previously isolated organisms, this was
taken as evidence that they incite the disease and was thus identified as pathogenic isolates.
Preparation of extracts
The plant samples, Aframomum melegueta (Alligator pepper) and Azadirachta indica
(Neem), were sorted to select the desirable ones. Those selected were spread in a laboratory
tray and dried in a moisture extraction oven at 65 0C for three hours. They were separately
ground in an Arthur Thomas laboratory mill, USA. They were afterwards sieved through a
1mm test sieve to obtain powdered processed plant materials.

A measured weight of each processed plant material was soaked separately in the
appropriate medium (i.e water and ethanol). The mixture was shaken and allowed to stand
for three hours. It was then filtered through Whatman No 42 filter paper. The filtrate was
evaporated to dryness over a water bath at low temperature (45-55 0C). The dried extract
was used for the test after reconstituting it with sterile distilled water. This was done by
embedding sterile paper discs into it and the discs were then used.
Determination of yield of extract
A measured weight (20 g) of each plant materials (A. indica and A. melegueta), was soaked
in excess of the extracting solvent and allowed to stand for three hours. It was shaken and
filtered. The filtrate was put in a weighed evaporation dish and evaporated to dryness. The
dish and extract was weighed after cooling in desiccators. By difference, the weight of
extract was obtained and expressed as a percentage of weight of sample analyzed. It was
calculated as shown below;
W2 – W1
100
Percentage yield =
X
W
1
W = Weight of processed sample analyzed
W1 = Weight of empty evaporation dish
W2 = Weight of dish and dried extract.
Sensitivity test on pathogens using the plant extracts
To determine how sensitive each pathogen isolate is to the two plant extracts, pure culture of the
isolates were directly inoculated on a sterile SDA plate. The extract was reconstituted in minimal
(1 mL) of sterile distilled water and embedded on sterile paper discs. The sterile paper discs were
placed on the surface of the inoculated plates and were incubated at room temperature for 7 days.

The cultures were examined for the presence of clear zones. The extent of inhibition
was determined by the diameter of the clear zones around the paper discs (Table 4).

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RAMESH PUTHETI et al.

Determination of minimum inhibition concentration
The minimum inhibition concentration of each extract was determined as the least
concentration of the extract which caused inhibition of the test organism.

The method involved reconstituting the extracts in dilutions of 0%, 25%, 50% and
100% of water and ethanol respectively.

A sterile paper disc was placed in each concentration and aseptically transferred to the
SDA plates inoculated with the isolates, incubated for 7 days and presence of clear zones if
any was measured and recorded.
Results and Discussion
Many different fungi was successfully isolated from different cassava tuber rots, they
include; Fusarium oxysporum, Fusarium solani, Botryodiplodia theobromae, Aspergillus
niger
and Penicillium oxalicum all of which were implicated as pathogens when tested on
healthy tubers (Table 1). Of all the isolated fungi, A. niger and F. oxysporum had the highest
percentage frequency of occurrence (Table 1), with A. niger being the most virulent,
exhibiting a dry rot contrary to the wetness that characterized the areas infected with
F. oxysporum.


Azadirachta indica and Aframomum melegueta showed some inhibitory activities on the
isolated fungi from the diseased cassava tubers. The extract of A. indica and A. melegueta
which showed no significant difference (p > 0.5) in yield was found to be fungitoxic on
F. oxysporum, P. oxalicum, A. niger and B. theobromae when used to control their
growth in vitro (Tables 2-6). The most inhibited was A. niger when A. melegueta was
extracted with ethanol (Table 5). In general however, A. indica proved to be more fungitoxic
than A. melegueta both with water and ethanolic extractions (Tables 2-6).
Table 2. Inhibition of some pathogens causing rot in cassava tubers using Azadirachta
indica
and Aframomum melegueta extracts.

A. indica
A. melegueta
Pathogen


Ethanol
Water
Ethanol
Water

F. oxysporum
11.2
9.1
10.4
7.5

P. oxalicum
12.6
11.8
15.3
10.0

A. niger
14.1
10.8
16.0
14.2
B. theobromae
13.4
12.2
8.6
8.1

Note: All dimensions are in mm and include the diameter of the disc.
Table 3. Minimum inhibition concentration for Azadirachta indica using ethanolic
extractions

Concentration, mg/mL

Isolate
0%
25%
50%
100%

A. niger
14.6
10.4
8.20
6.5

B. theobromae
15.6
9.20
-
-
F. oxysporum
12.4
-
-
-

P. oxalicum
13.8
10.6
-
-

Note: All dimensions are in mm and includes the diameter of the disc.

Post-Harvest Deterioration of Cassava
1279
Table 4. Minimum inhibition concentration for Azadirachta indica using water extractions.

Concentration, mg/mL
Isolate

0%
25%
50%
100%

A. niger
13.2
9.80
-
-

B. theobromae
13.80
-
-
-

F. oxysporum
9.80
-
-
-

P. oxalicum
12.4
-
-
-

Note: All dimensions are in mm and include the diameter of the disc.
Table 5. Minimum inhibition concentration for Aframomum melegueta using ethanolic
extractions.

Concentration, mg/mL

Isolate
0%
25%
50%
100%

A. niger
17.00
13.2
10.8
-

B. theobromae
10.60
9.40
-
-

F. oxysporum
10.90
8.50
-
-


P. oxalicum
16.20
14.10
9.30
-
Note:All dimensions are in mm and includes the diameter of the disc.
Table 6. Minimum inhibition for Aframomum melegueta using water extractions.
Concentration, mg/mL
Isolate
0%
25%
50%
100%
A. niger
14.80
12.50
9.80
-
B. theobromae
9.40
-
-
-
F. oxysporum
9.20
-
-
-
P. oxalicum
10.40
9.30
-
-
Note:All dimensions are in mm and include the diameter of the disc.

Water and ethanolic extractions showed no significant difference (p>0.5) in their rates
of fungitoxicity on A. niger, P. oxalicum, and F. oxysporum but exhibited a difference only
on B. theobromae inhibitions.

The different concentrations of both plant extracts used for MIC tests showed a
difference (P<0.5) among each other. The four tested fungi also showed a significant
difference in their different rates of susceptibility to ethanolic extractions of A. indica and A.
melegueta
. The different organisms showed no significant difference (P>0.5) in their
sensitivity to water extractions of A. indica but significantly differs (P<0.5) in their
sensitivity to water extraction of A. melegueta.

The isolated fungi with the highest rate of occurrence include; Aspergillus niger,
Fusarium oxysporum, Penicillium oxalicum, Botryodiplodia theobromae, Aspergillus flavus,
Rhizopus stolonifera and Trichoderma viride.
These correspond with previously isolated
microorganisms2-4,13. These organisms probably gained access into the tubers through the area
where the tuber is separated from the stem at harvest, or from the root tip which often got
broken during harvest, or through natural cracks and openings on the surface of the tubers.

The pathogenicity test showed Aspergillus niger as the most virulent organism, and in
culture, it is the most abundant. This suggests that A. niger could be the leading cause of post-
harvest deterioration in cassava especially here in south–east Nigeria from where all the samples
were obtained. This is a reconfirmation of the result obtained by Okigbo and Ikediugwu14 when
they reported A. niger as the most frequently occurring fungi in yam rot isolates.

Several works had been done on the use of plant materials as antimicrobial agents7-9,15, 16.
Azadirachta indica (Neem) was specifically shown to be fungitoxic by Amadioha and Obi8

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RAMESH PUTHETI et al.

when they used it’s seed extract to control the growth of collectotrichum lindemuthianum, a
cowpea fungus. Subsequently, Onifade9 also recorded the use of Neem leaf, bark, fruit and seed
in controlling C. lindemuthianum. Aframomum melegueta (Alligator pepper) extracts was used
by Okigbo and Ogbonnaya16 in the control of F. oxysporum and A. niger. Iwu17 also showed that
A. melegueta has antimicrobial and antifungal effects and also effective against schistosomes.

A. niger was the most inhibited when A. melegueta was extracted with ethanol. This showed
that A. niger is more sensitive to the active principle present in A. melegueta than that present in
A. indica. Since ethanolic extractions of both A. indica and A. melegueta are generally more
fungitoxic than water extractions, the active principles are probably more soluble in ethanol than
in water. This agrees with some workers who observed that factors like the type extracting
solvent and age of plant could influence the active principles present in plants18,19. B. theobromae
probably reacts differently to the two plants (A. indica and A melegueta) tested, this is because
the two plants showed a significant difference in their fungitoxicity only on B. theobromae, but
showed no difference on A. niger, F. oxysporum, and P. oxalicum inhibitions.
Conclusion
Since the results of this study have shown the potentials of extracts from A. indica leaves and
A. melegueta seeds to control the post–harvest rot of cassava, it would be necessary to adopt
them in prolonging the shelf–life of fresh cassava tubers since it is available, easily prepared
and with little or no adverse environmental effects. This will provide the much needed
economic benefits from cassava cultivation and production. Subsequent research in this area is
expected to identify the active principles that are present in this plant (A. indica and A.
melegueta)
and find ways of specifically using them in the control of these organisms.
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