ISOLATION OF MICROORGANISMS ASSOCIATED WITH DETERIORATION OF SWEET POTATO (Ipomoea batatas(L.) Lam) DURING STORAGE

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