ABSTRACT
Microorganisms associated with the sweet potatoes during storage were analyzed by isolation, characterization and identification. The bacteria belong to Erwinia spp isolated pathogenic fungi includes: Aspergillus Niger, Fusarium oxysporum, Aspergillus flavus, Rhizopus Stolonizer and Botryobiplodia spp respectively. Rhozopius sp has the highest percentage occurance of (27.3%) followed by Aspergilus niger (24.4%) and Aspergilus flavus (12.12%) has the least frequency percentage. Pathogenity test revealed that Rhizopus spp and Botryobiplodia sp is the most virulent and Aspergilus flavus is the least virulent fungus. The only isolated bacteria pathogen Erwinia sp (3.0mm) had rod shape and was gram negative. Spoilage of sweet potatoes during the storage is a major problem for both farmer and consumer. The study concluded that the one strains of spoilage bacteria and one strain of fungal should be taken into serious consideration during any proposed preservation methods of storage of sweet potatoes.
TABLE
OF CONTENTS
Title
page i
Certification ii
Dedication iii
Acknowledgements iv
Table
of contents v
List
of tables vii
List of figures viii
Abstract iv
CHAPTER 1
1.0 INTRODUCTION 1
1.1 Aims
and Objectives 4
CHAPTER 2
2.0 LITERATURE REVIEW 5
2.1 The Sweet Potato (Ipomoea batatas) 5
2.1.1 The
Origin 6
2.1.2 Cultivation
7
2.1.3 Nutrient
Content 8
2.2 Microbial
Spoilage of Potatoes 10
2.2.1 Rhizopus
Sp. 10
2.2.2 Sclerotinia screrotiorum 11
2.2.3 Botrytis Cinerea 12
2.2.4 Fusarium
oxysporum 13
2.2.5 Alternaria solani 14
2.2.6 Ralstonia solanacearum 15
2.3 Disease
and Pests 16
2.3.1 Fungal
Diseases 16
2.3.2 Nematodes
18
2.3.3 Insects 19
2.4 Harvesting,
Curing and Storage 21
CHAPTER 3
3.0 MATERIALS AND METHODS 22
3.1 Materials
22
3.2 Source of sweet potatoes 22
3.3 Media Preparation 22
3.3.1 Incubation of Culture Media 22
3.3.2 Subcutting/Purification
of Fungal Isolates 23
3.3.3 Incubation
of Culture Media 23
3.3.4 Characterization
and Identification of Bacterial Isolates 23
3.4 Gram
Staining Methods 23
3.5 Biochemical
Test 24
3.5.1 Motility Test 24
3.5.2 Catalase Test 24
3.5.3 Coagulase Test (Slide test) 24
3.5.4 Oxidase Test 25
3.5.5 Citrate Utilization Test 25
3.5.6 Indole Test 26
3.5.7 Voges-Proskauer Test 26
3.5.8 Methyl Red Test 27
3.5.9 Characterization and identification of fungi isolates using lactophenol 27
cotton blue staining
3.5.10 Pathogenicity Test (Test for spoilage potential
of the bacterial isolates) 28
3.6 Confirmation
of Isolates used in Pathogenecity Test 28
CHAPTER 4
4.0 RESULTS 29
CHAPTER 5
5.0 DISCUSSION AND CONCLUSION 34
5.1 Discussion
34
5.2 Conclusion
35
Reference 37
LIST OF TABLES
Tables Title
Page
1: Nutritional
Composition of Sweet Potato 9
2: Fungi isolated from sweet
potatoes samples 29
3 Identification
and characterize of Bacterial Isolates 30
4: Identification
and characterize of Macroscopic and 31
microscopic of the Fungal Isolates in sweet
potatoes
5: Percentages
occurrence of fungi isolated from the 32
infected sweet potatoes
6: Pathogenicity test on sweet potato for bacteria 33
CHAPTER
1
1.0 INTRODUCTION
Important root and of much nourishment to South East
region of Nigeria includes cassava, yam, sweet potatoes and Irish potatoes.
These tubers suffer from post harvest losses resulting from physical,
physiological and pathological factors or the combination of all the three. The
late blight diseases of potatoes, in Ireland in 1845 caused by phythophtora infestans,
was responsible for the famous Irish famine of 1845-1846, resulted in the death
and immigration of millions of people from the country to other countries such
as United State of America (Onuegbu, 2002).
The sweet potato (Ipomoea
batata (L) Lam) is a dicotyledomous plant that belongs to the family of
convolvulaceae. It is large, starchy, sweet tasting tuberous root. The young
leaves and shoots are sometimes eaten in greens. There are approximately 50
general and more than 100 species. Recognized two species in the section
batatas, which includes the sweet potatoes and subsequently there species have been added and one removed. The closet
with relative of the sweet potato appears to be Ipomoea trifida and Ipomoea
tabascan. Sweet potatos a creeping plants and the only economical species of
the family convolvulcae (Onuegbu, 2002).
Despite its nutritional importance, the tubers have
short storage life, generally, less than four weeks in the tropics. Their skin
is easily damaged during harvest and post harvest handling leaving the crops
highly perishable in microbial spoilage (FAO, 2008). Potato is an important
source of dietary fiber and in Great Britain, it contribute, 15% of the intake
of food. The starch tuberous roots are the major source of food for millions of
persons; the leaves are also useful sources of vegetable in some countries. The
plant originated in tropical American and they spend throughout the world.
Sweet potato is ranked seventh in the world’s
production after wheat, maize, Irish potatoes, rice barely and cassava (FAO,
2008). Sweet potatoes are of particular importance as food crops throughout
subtropics and tropical regions. The crop is one of important carbohydrate
sources for millions of people, particularly those in developing nations. Sweet
potatoes have nutritional value than Irish potatoes; especially in vitamins A,
B and C in calcium. China and Japan are the major consumers of sweet potatoes (Ameinyo
and Ataga, 2006). Post-harvest losses of all perishable tropical produce have
been conservatively estimated at 25% of production. Attack by fungi, bacteria
and viruses are probably the most serious causes of post harvest losses of
between 25% and 60% of the initial weight depending on variety when stored for
six and a half month in a semi sub-terranean. Ameinyo and Ataga (2006) reported
Rhizopus oryzae and Aspergillus niger as being responsible
for sweet potato rot. Reported fusarium
oxysporium, fusarium trichothecoides and fusarium radicicola to cause potato tuber rot under different
condition of temperature and humidity. The three sp were susceptible to rot
with higher relative humidity and higher temperature. The use of dry as well as
cool storage is therefore important in reducing the loss from fusarium rots of
potatoes.
However, the most common post-harvest storage disease
of potatoes as reported by Ameinyo and Ataga (2006) include Rhizopus soft (fusarium oxysporium) and black rot (Ceratocystis fimbriata). Different diseases arises after potatoes
are harvested, this is because the storage organs are essentially dormant
structure and their cells are physiologically unlike those of the growing plants.
The numerous diseases which occur in transit and storage result mainly from the
activity of fungi and bacteria. Investigations carried out by various workers
cleanly indicate that the real cause of the spoilage of tubers in transits or
storage result mainly from the activity of fungi and bacteria.
Investigation carried out by various workers clearly
indicate that the real cause of the spoilage of tubers in transit or storage is
the high temperature and injuries sustained by the tubers during the process of
marketing (Ameinyo and Ataga, 2006). Such disease considerable reduces the
commercial value of produce. Harvested tubers are vulnerable to attack by mucus
because of their moisture content and rich nutrient. Due to harvest, packing
and transportation, injuries of various binds are caused which facilitate the
entry of certain pathogens. Some of the pathogens produce extra cellular
enzymes and start degeneration process in advance of the fungal hypae or
bacterial cells of the attacking pathogens. As a result of infection, the
market and nutritive value of the tubers are reduced, either due to its ugly
appearance or the changes in the stored products of the tubers (Oyewale, 2006).
Recently, only while (i.e. uncut) sweet potato tubers
without apparent wounds were retailed maybe as a result of the difficult
economic situation in developing nations. Sweet potatoes are now halved
(depending on the size of the tuber and packed in polyethylene bags for
retailer. However, the potential for storage rot associated with these
practices has been given little attention and tubers showing various amounts of
damage are now commonly retailed in the open market. Bruised or cut tubers
readily become colonized by propagules of pathogens associated with the surface
and those from adjacent infected tubers. A wide variety of mucus particularly
moulds have been implicated in tuber spoilage. Relatively few are implicated as
primary pathogens.
1.1 AIMS AND OBJECTIVES
i. To
isolate, identify and characterize bacteria associated with deterioration of
sweet potato (Ipomoea batatas)
ii. To isolate, identify and
characterize fungi associated with deterioration of sweet potato (Ipomoea batatas)
iii. To determine the percentage occurrence of
bacteria and fungi associated with deterioration of sweet potato spoilage (Ipomoea batatas)
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