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