ABSTRACT

The identification of fungal pathogens responsible for the spoilage of cocoyam corms was demonstrated on Sabouraud dextrose agar media and subsequent microscopic observation. The fungi which were isolated from rot affected tissue identified to be the causative microorganisms responsible for cocoyam spoilage included Aspergillus niger, Sclerotium rolfsii, Fusarium solani, and Penicillium species. All the fungi were found to be responsible for spoilage of healthy cocoyam. Rot was observed by the softness of the corms and oozing out of fluids. Sclerotium rolfsii and Fusarium solani has the highest frequency of occurrence (56.3%) and 37.5% respectively followed by Aspergillus niger (31.2%) and Penicillium species with 18.7% frequency of occurrence. Pathogenicity test showed that the isolated fungal species induced rot in healthy cocoyam corms after days of inoculation. Sclerotium rolfsii and Fusarium solani were the most pathogenic with rapid deterioration of the fresh cocoyam corms in 21days having a rots diameter of 27mm and 22mm, respectively. The least pathogenic fungus was A. niger having a rots diameter of 16mm. This study showed that virulence varied amongst the fungal pathogens. S. rolfsii and F. solani were more virulent whilst Aspergillus niger, and Penicillium species were mildly pathogenic during the 28days storage period.

TABLE OF CONTENTS

Title Page i

Certification ii

Dedication iii

Acknowledgements iv

Table of Contents v

List of Tables vi

Abstract vii

CHAPTER ONE: INTRODUCTION

1.0 Introduction           1

1.1 Aim of the Study           8

1.2 Specific Objectives           8

CHAPTER TWO

2.0 Literature Review           9

2.1 Nutritional Composition of Cocoyams         11

2.2 Sources and Magnitude of Storage Losses in Cocoyam         13

2.2.1 Mechanical Injury         14

2.2.2 Physiological Factors                     14

2.2.3 Pathological Losses         15

2.3 Economic Importance of Rot                   16

2.4 Initiation of Rot         17

2.4.1 Causal Agents of Yam Rot         17

2.4.2 Root Rot Disease         18

2.5 Management of Pre-Harvest Pathogens of Cocoyam                       19

2.5.1 Biological and chemical control of rot organisms         20

2.5.2 Good Agronomic Practices, Field Sanitation and Store Hygiene         20

2.5.3 Thermal and Physical Control         21

2.5.4 Biological Control of Rot Organisms           21

CHAPTER THREE

3.0 Materials and Methods     24

3.1 Materials     24

3.1.1 Source of Cocoyam Species     24

3.2 Methods     24

3.2.1 Preparation of Culture Media                 24

3.2.2 Pathogen isolation     24

3.2.3 Subculturing and Purification     25

3.2.4 Characterization     25

3.3 Pathogenicity Test of the Isolated Fungi     26

CHAPTER FOUR

4.0 Results    28

CHAPTER FIVE

5.0 Discussion and Conclusion    33

5.1 Discussion    33

5.2 Conclusion    36

References    37