ISOLATION AND IDENTIFICATION OF FUNGI ASSOCIATED WITH COCOYAM SPOILAGE

ABSTRACT

This study focuses on the isolation and identification of fungi species associated with cocoyam spoilage (Colocasia esculenta). A total of twenty (20) cocoyam samples were selected from Michael Okpara University of Agriculture and National Root Crops Research Institute Umudike, Umuahia Abia State Nigeria farm. A total of three fungi species were isolated using standard microbiological methods. However, their percentage occurrence are Mucor spp 8(53.33%), Fusarium spp 5(33.33%) and Aspergillus spp 2(13.33%). They are pathogenic in nature. In this study, most microorganisms which tend to cause severe rot in cocoyam were observed. The severe rot/spoilage occurrence may be due to improper storage and harvesting of cocoyam and also due to injuries caused after harvest. The above fungi have been found to cause devastating rot blight complex which is a major threat to cocoyam production. But all these can be avoided by proper packaging and handling and use of clean planting equipment and healthy planting materials. Since cocoyam is a food plant consumed by a large population, great care and precaution should be taken in its handling, planting, storage, cooking and preservation.

TABLE OF CONTENTS

Title Page                                                                                                                                i

Certification                                                                                                                           iii

Dedication                                                                                                                              iv

Acknowledgements                                                                                                                v

Table of Contents                                                                                                                   vi

List of Tables                                                                                                                          vii

Abstract                                                                                                                                  ix

CHAPTER ONE

1.0       Introduction                                                                                                                1

1.1       Aim and Objectives                                                                                                    4

CHAPTER TWO

2.0       Literature Review                                                                                                       5

2.1       Scenario of Food Spoilage Worldwide (e.g. Cocoyam)                                            5

2.2       Food Spoilage Microorganisms                                                                                 8

2.2.1    Yeasts                                                                                                                         8

2.2.2    Molds                                                                                                                          10

2.3       Control of Rot and Spoilage of Agricultural Products                                               11

2.3.1    Good Agronomic Practices, Field Sanitation and Store Hygiene                            11

2.3.2    Thermal and Physical Control                                                                                    13

2.4       Biological Control of Rot Organisms                                                                         15

2.4.4    Chemical Control of Rots and their Causal Agents in Postharvest Produce                       16

CHAPTER THREE

3.1       Materials and Methods                                                                                               19

3.2       Source/Collection of Samples                                                                                    19

3.3       Materials and Media Used                                                                                          19

3.3.1    Sterilization of Materials                                                                                            19

3.4       Processing of Samples                                                                                                19

3.5       Microbiological Studies                                                                                             20

3.5.1    Preparation and inoculation of samples                                                                    20

3.6       Isolation of Fungi                                                                                                       20

3.7       Subculturing/Purification and Identification of Test Fungi Pathogens                    20

3.8       Identification of Fungal Isolates                                                                                 20

3.8.1    Wet Preparation                                                                                                          21

3.8.2    Colonial Morphology                                                                                                 21

CHAPTER FOUR

4.0       Results                                                                                                                        22

CHAPTER FIVE

5.0       Discussion and Conclusion                                                                                        26

5.1       Discussion                                                                                                                   26

5.2       Conclusion                                                                                                                  29

            References

            Appendix

LIST OF TABLES

CHAPTER ONE

1.0       INTRODUCTION

Two types of cocoyams are grown in South-eastern Nigeria and are both herbaceous plants. The most popular type available in most South-eastern Nigerian bazaar is ede-uli in Igbo (Colocasia esculenta); it grows in marshy areas and its corms are used as soup thickening agents in most South-eastern Nigerian communities. The second type which is less popular is called ede-oku in Igbo (Xanthosoma sagittifolium), whose corms could be boiled and eaten with various soups. Cocoyam (Colocasia esculenta) provide substantial portion of the carbohydrate content of the diet in many regions in developing countries and provide edible starchy storage corms or cormels (Agu et al., 2012). Cocoyam (Colocasia esculenta) of the Araceae family is a perennial monocotyledonous, herbaceous corm whose leaves grow upward, with fibrous root systems (Onwueme, 2008). The exact origin of cocoyam (Colocasia spp) is not clear, but it may have come from India or South-East Asia. They have a long history of cultivation. Ede-uli is further divided into edible and ornamental cocoyam. The ornamental cocoyam has three varieties namely; Colocasia black-magic, Colocasia coffee-cup and Colocasia black-ruffle. On the other hand, the ede-oku (Xanthosoma) comprises of species like; X. eggersii, X. sagittifollum, X. weeksi, and X. Violaceum Babajide (Oyewole, and Obadina, 2003). These are grown for their starchy corms, an important staple of tropical region (Oyewole, and Obadina, 2003). The cocoyam is known as food crop which provides high yield of roots (or corms) and foliage. It is a tropical food crop that can be grown under flooded or upland conditions (Agu, et al., 2016). The cocoyam plant is considered toxic due to the presence of calcium oxalate crystals typically as raphides (Purseglove, 2002). The toxin is minimized by cooking especially with a pinch of baking soda or reduced by steeping roots in cold water overnight (Purseglove, 2002). Calcium oxalate is highly insoluble and contributes to kidney stones. Cocoyam contributes significant portion of the carbohydrate content of the diet in many regions in developing countries and provides edible starchy storage corms and cormels. Although they are less important than other tropical roots such as yam, cassava and sweet potatoes, they are still a major staple in some parts of the tropics and sub tropics (Oyewole, and Obadina, 2003). It could be used as thickener in soup, flour (for confectionary), or may be cut up and boiled or fried to make crispy chips or flakes. The leaf stalk can also be eaten. Post-harvest spoilage of cocoyam arises from improper handling of the cocoyam either during storage or harvest. The greatest cause of root rot and tuber loss in storage is the highest disease in cocoyam (International Institute of Tropical Agriculture, 2008).

Cocoyam (Colocasia esculenta) grows to a height of 1-2 metres, the plant consist of central corn (lying just below the soil surface) from which leaves grow upward, roots grow downwards, while cormels, daughter corms and runners (stolons) grows laterally, the root systems is fibrous and lies mainly in the top one metre of soil (Onwueme, 2008). Colocasia esculenta is known as food crop which provides high yield of roots (or corms) and foliage, it is a tropical food crop that can be grown under flooded or upland conditions (Chayty et al., 2007). However, various lines of ethnobotanical evidence suggest that Colocasia esculenta originated from south central Asia, probably in India of the Malay peninsula (Kolchaar, 2006). Wild forms occurs in various parts of south eastern Asia (Purseglove, 2002), hence south east Asia is said to be an important region for ethnobotanical and genetic diversity of Colocasia esculenta. From its centre of origin, it spread east ward to the rest of South –East Asia and to China, Japan and the Pacific Islands. From Asia it spread west ward to Arabia and the Mediterranean region. It arrived on the east coast of Africa over 2,000 years ago. It was taken by voyagers, first across the continent of Africa, and later on slave trade to the Caribbean. Today Colocasia esculenta is pantropical in its distribution and cultivation. The largest area of cultivation is in West Africa, which therefore account for the greatest quantity of production. Significant quantities of taro are also grown in the Caribbean and virtually in all humid and sub-humid parts of Asia (Purseglove, 2002). More so, Colocasia esculenta is grown in about 30 countries, either in flooded wetland or in uplands.

The bulk of its production is in Africa (Spore, 2003). The need to achieve food security in Nigeria has generated increased interest in research, production and consumption of cocoyam. According to (FAO, 2006) Nigeria is the largest producer of cocoyam in the world, accounting for about 37% of the world’s output estimated to annual production of 5.49 million metric tones, followed by Ghana which producers 31%, conversely (Eze and Okorji, 2003) documented that Nigeria accounted for about 40% of total world’s output of cocoyam, thus from the evidence, the cultivation of cocoyam in Nigeria is declining (Onyenweaku and Eze, 2007; Zuhair and Hunter, 2000). Production of cocoyam has not been given priority attention in many countries, probably because of its inability to earn foreign exchange, as well as its unacceptability by the high income countries for both consumption and other purposes (Onyenweaku and Eze, 2007). However, it is widely perceived that cocoyam production and processing in the country does not keep pace with other major root and tuber crops (Asumugha and Mbanaso, 2002), this is believed to be attributed to its declining yields, low storability and the socio – cultural perception of the crop as women’s crop, as women do not have control over land, labour and capital in some parts especially South –eastern Nigeria (Coursey, 2004; Spore, 2003), this is worsened by the devastating disease, cocoyam root rot blight complex (CRRBC) which is a major threat to cocoyam production. The use of chemicals has helped in control of rot but due to the identifiable problems (eg. chemical residues, biodegradation, phytotoxicity, pollution, development of resistance in target organism, high cost, atimes non availability and hazard to man and his environment) renders them either slow to adopt by farmers or farmers have totally failed to adopt them, for one cultural reasons or the other (Okigbo and Odurukwe, 2009), hence alternative control methods are employed. Presently considerable efforts are directed at exploring the potentials of botanicals (plant extracts) as alternatives or complimentary to synthetic chemicals. Botanicals have the advantage of not only being readily available and affordable but are also sources of non-phytotoxic and easily biodegradable alternative fungicides and antibiotics, hence environment friendly (Akuesh et al., 2002; Okigbo and Nmeka, 2005; Okigbo and Omodamiro, 2006).

1.1       AIM AND OBJECTIVES

To isolate and identify fungi associated with cocoayam spoilage, while the specific objectives are;

1.     To identify/characterise these fungal pathogens

2.     To determine the factors encouraging spoilage of cocoyam

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