ABSTRACT

The microorganisms responsible for spoilage in white sweet potato roots (TIS/87/0087 variety) were isolated, characterized and identified. The isolated pathogenic fungi were Aspergillus sp, Botryodiplodia sp Rhizopus sp, Fusarium sp. Of these pathogens, Rhizopus sp has the highest percentage occurrence of (27.3%) followed by Aspergillus niger (24.24%) and Aspergillus flavus (12.12%) has the least frequency percentage. The pathogencity test revealed that Rhizopus sp and Botryodiplodia sp is the most virulent and Aspergillus flavus is the least virulent fungus. The only isolated bacteria pathogen Erwinia sp (3.0mm) had rod shape and was Gram negative, proper storage facilities, essential control measures is therefore important in reducing the loss of sweet potato tubers during storage.

TABLE OF CONTENTS

Title Page i

Certification ii

Dedication iii

Acknowledgements iv

Table of Contents v

List of Tables ix

Abstract x

CHAPTER ONE 

1.0 Introduction 1

1.1 Aims and Objective 3 

CHAPTER TWO 

2.0 Literature Review 4

2.1 The Sweet Potato (Ipomoea Batatas) 4

2.1.1 The Origin 5

2.1.2 Cultivation 5

2.1.3 Nutrient Content 7

2.2 Microbial Spoilage of Potatoes 9

2.2.1 Rhizopus sp 9

2.2.2 Sclerotinia sclerotiorum 10

2.2.3 Botrytis cinerea 11

2.2.4 Fusarium oxysporum 12

2.2.5 Alternaria solani 13

2.2.6 Ralstonia solanacerum 14

2.3 Disease and Pests 15

2.3.1 Fungal Diseases 15

2.3.2 Nematodes 16

2.3.3 Insects 17

2.4 Harvesting, Curing and Storage 18

2.4.1 Harvesting 18

CHAPTER THREE 

3.0 Materials and Methods 20

3.1 Materials 20

3.2 Methods 20

3.2.1 Sample Collection 20

3.2.2 Preparation of Media 20

3.2.3 Isolation of Bacteria from Post Harvest

Deterioration of Sweet Potato 20

3.2.4 Isolation of Fungi from Post harvest Deterioration of Sweet Potato 21

3.2.5 Subculturing/Purification of Bacteria Isolates 21

3.2.5.1 Incubation of Culture Media 21

3.2.6 Subculturing/purification of fungal isolates 21

3.2.6.1 Incubation of culture media 21

3.2.7 Characterization and identification of bacterial isolates 22

3.2.7.1 Gram staining method 22

3.2.7.2 Biochemical Test 22

3.2.7.3 Coagulase test 22

3.2.7.4 Oxidase test 22

3.2.7.5 Indole test 22

3.2.7.6 Urease test 23

3.2.7.7 Methyl red test (MR) 23

3.2.7.8 Vogesproskauer test 23

3.2.7.9 Citrate utilization 23

3.2.7.10 Sugar fermentation test 23

3.2.7.11 Catalase production test 23

3.2.7.12 Hydrogen sulfide (H_2 S) production test 24

3.2.7.13 Motility test 24

3.2.7.14 Nitrate test 24

3.3 Characterization and Identification of Fungal Isolates 24

3.3.1 Pathogenicity Test 24

3.3.2 Confirmation of Isolates used for Pathogenicity Test 25 

CHAPTER FOUR 

4.0 Results 26

CHAPTER FIVE 

5.0 Discussion, Conclusion and Recommendation 33

5.1 Discussion 33

5.2 Conclusion 34

5.3 Recommendations 34

REFERENCE 35

APPENDIXES      39

LIST OF TABLES

Table Title      Page 

2.1 Nutritional composition of Sweet Potatoes 8  

4.1: Fungi isolated from the spoilt sweet potato 26

4.2: Percentage occurrence of Fungi isolated from 

 the spoilt sweet potato 27

4.3: The Fungi pathogenicity test on spoilt sweet potato. 28

4.4: Macroscopic and microscopic characterization 

of isolated microorganism. 29

4.5: The bacteria pathogenicity test on sweet potato. 30

4.6: Biochemical and microscopic characteristic of bacteria isolates. 31