Fungi Associated With The Spoilage Of Cocoyam In The Field

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