ABSTRACT
Microorganisms associated with decayed pawpaw fruits were isolated and identified. Following sample preparation and serial dilutions, diluents of each sample were plated out in duplicates on nutrient agar and sabouroud dextrose agar using pour plate and spread plate methods. A total of seven fungal species, Aspergillus spp, Mucor spp, Penicillium spp, Fusarium spp, Yeast, Monilia spp, and Rhizopus spp were identified. Lactobacillus spp, Escherichia coli, Bacillus spp, Staphylococcus spp, Pseudomonas spp, and Proetus spp were the identified bacterial isolates. In fungi Aspergillus spp had the highest percentage occurrences (100%) while Monilia spp had the least percentage occurrences (28.57%). In bacterial Pseudomonas spp had the highest percentage occurrences of (71.43%) while Lactobacillus spp had the least percentage occurrence of (28.57%). Results of pathogenicity test showed that four fungal species were able to cause decay in healthy pawpaw fruit, including Aspergillus spp, Penicillium spp, Fusarium spp, Monilia spp. These isolates that cause rot were considered causative agent for spoilage of pawpaw fruits.
TABLE OF CONTENTS
Title Page i
Certification ii
Dedication iii
Acknowledgement iv
Table of Contents v
List of Tables viii
Figure ix
Abstract x
CHAPTER ONE
INTRODUCTION 1
1.1.1 Statement of Problem 5
1.1.2 Research Objective 5
CHAPTER TWO
LITERATURE
REVIEW 6
2.1 Classification 7
2.2 Origin and Distribution7
2.3 Botanical
Description 10
2.4Types
of Papaya 13
2.5 Growth habit and
Soil16
2.6 Pollination
17
2.7 Propagation
18
2.8 Harvesting 18
2.9 Nutritional
value
19
2.10 Economic
Importance 20
2.11 Industrial Importance
20
2.12 Chemical Compounds 21
2.13 Toxicity and Allergy
22
2.14 Health Benefits 23
2.15 Insect Pests and
Nematodes
28
2.16 Diseases of Papaya 31
CHAPTER THREE
3.0 Materials and Methods
37
3.1 Sample Collection 37
3.2.1 Media Preparation
37
3.2.2 Sample Preparation 37
3.2.3 Isolation of
microbial isolate from decayed pawpaw fruits 38
3.3.1 Direct placement
technique 38
3.3.2 Characterisation
and identification
38
3.3.3 Characterisation of
fungal isolates
39
3.4.1 Characterisation of
bacteria isolates
39
3.4.2 Biochemical test 39
3.4.3 Gram staining
39
3.4.4 Catalase test 40
3.4.5 Citrate test
40
3.4.6 Coagulase test 40
3.4.7 Indole test41
3.4.8 Voges Proskeur test
41
3.5.1 Sugar fermentation
test 41
3.5.2 Oxidase test
42
3.5.3 Methyl-red test 42
3.6 Pathogenicity test
42
CHAPTER FOUR
4.0 Results
44
CHAPTER FIVE
5.0 Discussion
48
5.1 Conclusion
50
5.2 Recommendation
50
REFERNCES
51
APPENDIX
59
LISTS OF
TABLE
Tables
1
2
3
4
5
6
7
8
|
Title
Production of papaya by region
Fruit characteristics of papaya cultivars in major
producing countries
Chemical components of 100g orange-fleshed papaya
fruit
Nutrient
Occurrence of bacteria isolate in
decay pawpaw fruit
Occurrence of fungal isolate in decay
pawpaw fruit
cultural,
morphological, biochemical characteristics of bacterial isolates from pawpaw
fruit
Microscopic and morphological
identification of fungal isolate
pathogenicity test of fungal isolates
|
Pages
9
14
24
45
46
47
48
49
|
LIST OF FIGURES
Title
Page
1 Papaya Major Producing Countries 9
CHAPTER ONE
1.0
INTRODUCTION
Fruits are very important and have high dietary and
nutritional qualities (Barth et al., 2009). Studies have evaluated the
association of fruit and vegetable consumption with the reduction of risk of
specific diseases (Hung et al., 2004). Their consumption has
dramatically increased by more than 30% during the past few decades (Barth et
al, 2009). Fresh fruits and vegetable consumption increased by 25.8% to 32.6%,
respectively, and far exceeded the increases observed for processed fruit and vegetable
products. It is also estimated that about 20% of all fruits and vegetables produced
is lost each year due to spoilage (Barth et al., 2009). Raven, et al.,
(2005) reported that 20 new human fungal pathogens are documented each year. It
is estimated that about 20-25% of the harvested fruits are decayed by pathogens
during post-harvest handling even in developed countries (Droby, 2006; Zhu,
2006).
Deterioration of foods generally is attributed to two
main causes which are natural degradation due to activities of enzymes and
growth of microorganisms (bacteria, molds and yeasts). These microorganisms can
result in useful products through their activities particularly during
fermentation of foods such as wine and cheese. The negative effects of these
microbial activities result in decay, rotting of food and food poisoning hence
the basis of microbial food spoilage occurs when these microorganisms release
their own enzymes into the foods and absorb the nutrients thereby changing the
physical and chemical states of the foods; thus lowering the nutritional value.
Bacteria and fungi may also produce waste products which act as poisons or
toxins, thus causing the renowned ill-effects (Bakriet al., 2010)
Pawpaw (Carica papaya) is a popular fruit plant
grown all over the wetter parts of West Africa, tropical and subtropical
regions of the world being one of the most nutritious and cheapest fruits grown
and consumed in Nigeria (Baiyewu, 1994). It is usually grown as compound fruit
crop or semi-wild fruit crop from discarded seeds (Kutheet al., 1974).
Pawpaw (Carica papaya) is a member of the small family “Caricaceae”
allied to the “passifloracea”.which
incorporates 35 latex-containing species in six genera, Carica, Cylicomorpha,
Jarilla, Jacaratia, Horovitzia and Vasconcellea (Badillo, 2002)
with the genus Carica, consisting of only one species. Although opinions
differ on the origin of C. papaya, it is likely that C. papaya originates
from the lowlands of eastern Central America, from Mexico to Panama (Nakasone et
al., 1998). It is a fast growing, short-lived, woody, large herbaceous
plant having latex vessels in all its fruits with an upright unbranched stem
covered all over with leaf scars (Agnew, 1968; Dick, 2003). It generally only
branches when injured (Garret, 1995). The stem is hollow with a light green to
a tan brown colour bearing leaves that are large and deeply palmately lobed
with the older leaves abscising as new leaves emerge (Morton, 1987). The papaya
fruit is melon-like, oval to nearly round, elongated club–shaped and is rich in
latex when unripe with a green coloured skin. As it ripens, it becomes light or
deep yellow externally and the thick wall of succulent flesh becomes aromatic
yellow-orange or various shades of red. The fruit is then juicy, sweetish and
some types are quite musky (Morton, 1987). The fruit consist largely of water,
sugar, vitamins A and C, protein and ash (Baiyewu, 1994). It is an interesting
tree in that the male and female parts exist in different trees. Pawpaw Fruits,
apart from being taken as food also have some medicinal importance. It has a
mild laxative action and the fruits, leaves and seeds are used medicinally
against worm and ulcer (Baiyewu, 1994). Its main medicinal use is as a
digestive agent; it is prescribed for people who have difficulty digesting
protein and is used to break up blood clots after surgery, which is due to the
presence of enzymes papain in the plant’s latex. The latex from the trunk of
the tree is also applied externally to speed the healing of wounds, boils and
warts. The seed is used to expel worm and the flower may be taken in an
infusion to induce menstruation. It has also been reported that
annonaceousaceto genus derived from the extract of the twigs of the pawpaw tree
may be good chemotherapeutic agents for cancer as these compounds inhibit
enzymes necessary for metabolic processes in tumour cells. Increasing interest
in medicinal herbs has increased scientific scruting of their therapeutic
potentials and safety thereby providing physicians with data to help patients
make wise decisions about their uses.
Economically, carica papaya (pawpaw) is the most
important species within the Caricaceae, being cultivated widely for
consumption as a fresh fruit and for use in drinks, candies and as dried and
crsystallised fruit (El Moussaoui et al., 2001). Nutritionally, papaya
is a good source of calcium.
Papaya also has several industrial applications due to
the proteolytic enzyme called papain hence their use in the production of
chewing gums, tenderizing meat and drug preparation for various digestive
ailments and for the treatment of gangrenous wounds as well as in the textile
and cosmetics industries (Kochhar, 1986; Villegas, 1997). Biochemically, its
fruits are good sources of several proteins and alkaloids with application to
pharmaceutical, food, industries, e.t.c. (El Moussaoui et al., 2001).
The seed is used to expel worms and the flower may be taken in an infusion to
induce menstruation (Duke, 1984 and Oduola et al., 1986). Increasing
interest in medicinal herbs has increased scientific scrutiny of their
therapeutic potentials and safety thereby providing physicians with data to
help patients make wise decisions about their use (“O”Hara et al.,
1998).
Papaya fruits are beset with problems of field and
storage rot. Gutpa and Pathak (1986) identified 22 different fungi in
post-harvest decay of papaya fruits which include Aspergillus niger,
Aspergillus flavus, Rhizopus oryzae, Fusarium moniliforme. Bacterial
pathogens involved with rot of papaya include the species of soft-rotting Erwinia,
Pseudomonas, Xanthomonas, Cytophaga and Bacillus (Liao et al., 1987;
Lund, 1983). These microorganisms, under the influence of environmental factors
(include temperature, hydrogen ion concentration (pH), oxygen, moisture
content) pose a serious threat to papaya fruit production. Besides the losses
in income to the papaya fruit marketers, the rotten fruits could also cause a
health hazard to consumers. Krogh (1992) had earlier reported that most
microbes infecting plant tissues often produced secondary metabolites in their
hosts, which are known to be hazardous to animals including man. Some of these
metabolites include the ergot alkaloids on cereals by Clavisep spp, fumonisin on maize by Fusarium
spp, aflatoxins and
ochratoxinson several plants produced by Aspergillus spp (Prasad, 1992). Nigeria is the
third largest producer of papaya in the world with 703,800 metric tons (FAO,
2010), it’s plentiful and sold all year round as well as being globally
consumed by people for multiple benefits hence, the need for preservation and
to boost its production. This can be achieved among other things by preventing
the occurrence of these diseases through studying the ecology of the microbes.
1.1
STATEMENT OF PROBLEM
Papaya is a useful plant with nutritional, medicinal
and health benefits. In spite of all these benefits, the plant is besieged by
lots of pathogens both in the field and post-harvest diseases and these
diseases result in yield losses thus making its valuable components
unavailable. The papaya farm in Covenant University is particularly useful as a
source of raw materials for the production of some patented products. This farm
is however, infested with pathogens on fruits, stems, and leaves resulting in huge
yield losses making the desired raw materials unavailable.
1.2 RESEARCH
OBJECTIVES:
• To isolate the microorganisms associated with the
rot diseases of fruits, stems and leaves of papaya
• To identify and characterize the isolated
microorganisms.
• To determine the pathogenicity of the isolated
microorganisms for papaya.
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