Identification Of Fungi Associated With The Spoilage Of Cocoyam

Description

ABSTRACT

Fungi associated with the spoilage of cocoyam (Colocasia esculenta) during storage was investigated in this study. Pure isolates of five storage rot causing fungi of cocoyam (Colocasia esculenta) (L)Schott) corms were assessed for their potency in causing rot of the corms during storage. The isolates were Sclerotium rolfsii Sacc., Botryodiplodia theobromae Pat., Fusarium solanii (Mart) Sac., Fusarium SP. and Rhizopus stolonifer (Ehren ex. Fr) Lind. Each of the fungal organisms were inoculated on five corms of cocoyam free from blemish and were left for two weeks after which the extent of rot was determined by assessing both the area and volume of rot caused by each pathogenic fungus. S. rolfsii and B. theobromae proved most potent in causing rot with mean percentage volume of 14.50 cm³ and 10.14cm³ respectively. The area of rots caused by these two fungal organisms was again significantly higher (P≤0.05) than the rest. The least pathogenic organism was R. stolonifer with only 3.10cm³ mean volume of rot caused and less than 2 cm² mean area of rot. Fungal hyphae penetrated the corms of cocoyams from cell to cell both inter-and intra- cellularly in the carbohydrate rich storage parenchyma.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

1.0      INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• PROBLEM STATEMENT
• AIM OF THE STUDY
• OBJECTIVE OF THE STUDY
• SIGNIFICANCE OF THE STUDY
• SCOPE OF THE STUDY
• PROJECT ORGANISATION

CHAPTER TWO

LITERATURE REVIEW

• OVERVIEW OF COCOYAM
• METHODS OF STORAGE TO PREVENT/CONTROL FUNGI ASSOCIATED WITH THE SPOILAGE OF  COCOYAM DURING STORAGE
• NUTRITIONAL VALUE OF COCOYAM
• PRESERVATION OF COCOYAM
• USES OF COCOYAM
• BENEFITS OF COCOYAM

CHAPTER THREE

• MATERIALS AND METHODS
• COLLECTION OF MATERIALS FOR THE STUDY
• PATHOGENICITY ASSESSMENT STUDIES OF FUNGAL ORGANISMS
• DETERMINATION OF HOST-PATHOGEN INTERACTIONS

CHAPTER FOUR

• RESULT AND DISCUSSION

CHAPTER FIVE

• CONCLUSION
• RECOMMENDATION
• REFERENCES

CHAPTER ONE

1.0                                          INTRODUCTION

Cocoyam is widely cultivate and used for food in Nigeria, Ghana and other countries including China.  China and Ghana leading in world production [Agu, K. C, 2014].

Although its production has increased from 643000 to 1.7 million tones during the past decade, its contribution to root-crop production increased from only 39-6.8%.  In Nigeria, Colocasia species are the most important food and the third most important root/tuber crop after yams and cassava [Agu, K.C., Awah, 2016]. Besides critical contribution to the national food security and cash  income  producing nations, cocoyam  are also being considered as source of starch for use in biodegradable film materials and for other industrial and pharmaceuticals purposes because of interesting properties of the amylopectin fraction of starch, which is the principal form of cocoyam starch [Eleazu C. O., Iroaganachi M., and Eleazu K. C., 2013].

Cocoyams have very short post harvest storage life of a few days to weeks. Differing and often conflicting reports have been made on the post harvest losses of cocoyam. But it bears nothing that post harvest storage life is often short and biodegradative losses are extensive and up to 100% losses are common due to the fungi which associates with the spoilage of cocoyam during storage condition [Agu, K.C., Awah, 2016].

However, substantial post harvest losses caused  by the fungi associated with the spoilage  of cocoyam tubers during storage is attributed to a number of physical, physiological damage  arising  from harvesting, storage or transportation have  often been implicated as some of the predisposing factors  to cocoyam spoilage or deterioration. Invasion by pathogens either through natural openings or wounds is considered the most critical factor in cocoyam spoilage [Osuji, J.O, 2013].

A wide range of micro-organisms (Particularly moulds) have been associated with cocoyam decay, relatively few are implicated as primarily pathogens. The degree of pathogenicity varies and is highly dependent upon storage conditions. It has been stated that fungi take the lead in the spoilage of cocoyam during storage. Under these storage conditions, the fungi which are liable to  attack cocoyam include; Fusarium  solani, Botryodiplodia, theobromae, Rhizopus, stolonifer, Aspergillus  niger, Sclerotium roltsii, Trichoderma hamatum and Pythium species. Another factor also attributed to the spoilage of cocoyam is high respiratory activity. Storage temperature to an optimum of 70C and 85% relative humidity increases the storage time. The crops are usually left in the ground and harvested when need, and there  is a limit to how long the crop can be left in the soil since the corms and cormels sprout and produce new growth, which result  in the cocoyam losing its good values [Osuji, J.O, 2013].

Therefore, it has been suggested that November and March /April are the ideal time for harvesting cocoyam. However, due to the difficulties in storage, cocoyam are usually utilized or consumed fresh shortly after harvest because of these fungi which lead to their spoilage during storage [Osuji, J.O, 2013]. The objective of this study is to investigate the fungi associated with the spoilage of post harvest cocoyam during storage at ambient temperature (28 ± 20C).

Cocoyam leaves are consumed as green or dry vegetables and the stem is either cooked or eaten on its own or together with other dietary staples or pound into flour. The leaves are consumed because they are rich in protein and vitamins while the roots is rich in carbohydrates and minerals [Onuegbu, B.A, 2012]

Large quantities of carbohydrate-rich solid waste are produced in the course of processing cormels into starch and this constitute a waste disposal problem [Agu, K.C., Awah, 2016].

The changing economic, social, political and cultural values of the world have challenged all countries to efficiently use their resources.

In Cameroon, two types of cultivated cocoyam varieties can be differentiated based on the colour of the flesh. The white –flesh cultivar or white cocoyam is the main cultivated variety because of its early maturation (6-(months) and high yield. In addition, the white cocoyam is most preferred in diet because of its excellent taste. The pink-flesh variety or red cocoyam is rarely grown because of its long maturation process (12-16months) Despite its importune, white cocoyam is highly susceptible to cocoyam    root  with attendant yield losses > 90%.  In contrast, fields observations by farmers revealed that the red cocoyam has a certain degree of field tolerance against the cocoyam root rot   disease [Onuegbu, B.A, 2012].

1.2                                           BACKGROUND OF THE STUDY

Cocoyam is a common name for more than one tropical root crop and vegetable crop belonging to the Arum family (also known as Aroids^{[ Agu, K.C., Awah, 2016]} and by the family name Araceae).

Cocoyams are herbaceous perennial plants belonging to the family Araceae and are grown primarily for their edible roots, although all parts of the plant are edible. Cocoyams that are cultivated as food crops belong to either the genus Colocasia or the genus Xanthosoma and are generally composed of a large spherical corm (swollen underground storage stem), from which a few large leaves emerge. The petioles of the leaves (leaf stems) stand erect and can reach lengths in excess of 1 m (3.3 ft). The leaf blades are large and heart-shaped and can reach 50 cm (15.8 in) in length.

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, K. C., Awah, N. S., Sampson, P. G., Ikele, M. O., Mbachu, A. E., Ojiagu, K.D. Okeke, C.B., Okoro, N.C.N. and Okafor, O.I., 2014.]. Cocoyam (Colocasia esculenta) of the Araceae family is a perennial monocotyledonous, herbaceous corm whose leaves grow upward, with fibrous root systems. 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[Agu, K. C., Awah, N. S., Sampson, P. G., Ikele, M. O., Mbachu, A. E., Ojiagu, K.D. Okeke, C.B., Okoro, N.C.N. and Okafor, O.I.2014.]. These are grown for their starchy corms, an important staple of tropical region [Agu, K. C., Awah, N. S., Sampson, P. G., Ikele, M. O., Mbachu, A. E., Ojiagu, K.D. Okeke, C.B., Okoro, N.C.N. and Okafor, O.I.2014]. 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, K.C., Awah, 2016]. The cocoyam plant is considered toxic due to the presence of calcium oxalate crystals typically as raphides [Purseglove, J.W, 2016]. The toxin is minimized by cooking especially with a pinch of baking soda or reduced by steeping roots in cold water overnight [Purseglove, J.W, 2016]. 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 [Agu, K. C., Awah, N. S., Sampson, P. G., Ikele, M. O., Mbachu, A. E., Ojiagu, K.D. Okeke, C.B., Okoro, N.C.N. and Okafor, O.I.2014]. 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 [Osuji, J.O, 2013]. The post-harvest loss of root and tuber crops has been a very serious problem to farmers, as more than 40% of their harvest maybe list because of decay [Eleazu C. O., Iroaganachi M., and Eleazu K. C., 2013]. It is estimated that in the tropics each year between 25% and 40% of stored agricultural products are lost because of inadequate farm and village-level storage [Eleazu C. O., Iroaganachi M., and Eleazu K. C., 2013].The principal species of microorganism associated with cocoyam rot in Nigeria are; Aspergillus flavus, Penicillium digitatum, Botryodiplodia theobromae and Erwinia carotovora [Eleazu C. O., Iroaganachi M., and Eleazu K. C., 2013]. These fungi are believed to be pathogenic to various cultivars of cocoyam, causing rot of several parts of Southern Nigeria [Ogbo, F.C. and Agu, K.C.2015]. Fungi spoils the cocoyam by colonizing it by depolymerizing certain specific cell wall polymers such as proto-protein, the cementing substance of the produce [Onuegbu, B.A, 2012].

Also cocoyams may be attacked by pests like mealybug, aphids, catapillers etc. these pests and diseases can be controlled by the use of chemicals, fertilizers rich in potassium. Insecticides from nurseries (for pests) use of well cleaned planting materials, initiation of early planting (April/May) and planting in well-drained soil with no water logging [Ogbo, F.C. and Agu, K.C.2015].

1.2                                   PROBLEM STATEMENT

It has been stated that fungi take the lead in the spoilage of cocoyam during storage. Under these storage conditions, the fungi which are liable to attack cocoyam include; Fusarium solani, Botryodiplodia, theobromae, Rhizopus, stolonifer, Aspergillus niger, Sclerotium roltsii, Trichoderma hamatum and Pythium species, and this led to substantial post harvest losses and this spoilage during storage is attributed to a number of physical, physiological damage  arising  from harvesting, storage or transportation have  often been implicated as some of the predisposing factors  to cocoyam spoilage. This study is helpful to identify that fungus and makes a provision to increase storage [Purseglove, J.W, 2016].

1.3                                       AIM OF THE STUDY

This study is aimed at isolating and characterizing various fungal species associated with cocoyam spoilage with a view of highlighting and describing the types of fungal rots associated with post-harvest loss of cocoyam.

1.4                              OBJECTIVES OF THE STUDY

Specific objectives of this study were as follows:

1. To identify the socio-economic characteristics of cocoyam/cocoyam storage;
2. To identify five different fungus associated with spoilage of cocoyam
3. To identify and discus different methods of storage to prevent/control fungi associated with the spoilage of  cocoyam during storage        
4. To assess profitability of cocoyam production; and
5. To investigate production constraints

1.5                             SIGNIFICANCE OF THE STUDY

This study is useful to farmers, marketers and consumers of cocoyam in that it will help them to upgrade their storage experience and capacity which improves their lives and markets[Eleazu C. O., Iroaganachi M., and Eleazu K. C., 2013].

1.6                                                   SCOPE OF THE STUDY

Constraints on cocoyam production indicated that it is not due to lack of demand but losses due to field and especially post-harvest deterioration. Fungi are the main microbial pathogens that cause storage rot of cocoyam corms. Fungi causing storage rot of cocoyams have been reported.

Fungi reported as important rot pathogens include Fusarium solani (Mart) Sacc, F. oxysporium Schl; F moniliforme wr. Et Reg; F. avenaceum (Fr.) Sacc; Botryodiplodia theobromae Pat; Sclerotium rolfsii Sacc; Botrytis sp; Pythium sp, Phytophthora colocasiae Rac. Rhizoctonia bunoides (Berk and Br.) Sacc. In Nigeria, B theobromae, S. rolfsii, F. salani, F. oxysporium, Fusarium sp; and R. stolonifer have consistently been reported as rot pathogens consistently isolated from corms of C. esculenta, C. antiquorum and X. sagittifolim during storage. These fungal organisms have also been reported to be the major cause of storage rots of cocoyam [Awah, N.S., Okeke, C.B, 2016].

Quantitative pathogenic losses of the stored cocoyams result from the rapid and extensive break down of host tissues by microorganisms especially fungi. The pattern of attack is usually an initial infection normally through wounds caused by harvest bruises and points of detachment from mother corms by one of a few specific pathogenic or saprophytic organisms which grow on the dead moribund tissues remaining from the primary infection [Awah, N.S., Okeke, C.B, 2016].

1.7                                                         PROJECT ORGANISATION

The work is organized as follows: chapter one discuses the introductory part of the work,   chapter two presents the literature review of the study,  chapter three describes the material and methods applied,  chapter four discusses the results and discussion of the work, chapter five summarizes the research outcomes and the recommendations.