SPOILAGE RELATED FUNGI IN COLOCASIA ESCULENTA (COCOYAM)

1.1 Introduction

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, (Duru and Uma, 2002). Large quantities of carbohydrate-rich solid waste are produced in the course of processing cormels into starch and this constitutes a waste disposal problem, (Duru, 2000). The changing economic, social, political and cultural values of the world have challenged all countries to efficiently use their resources.

In Nigeria, 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 (Tambong, 2000).

As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Limitation of the study and Definition of terms.

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1.2 Background of 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.

Therefore, in Nigeria where the research was carried out, the activities that was conducted is to know the Spoilage Related Fungi in Cocoyam.

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1.3 Statement of Problems

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).

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1.4 Aim and Objectives of 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.

Specifically, the objectives needed to achieve the above stated aim, are stated 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 assess profitability of cocoyam production;
4. To investigate production constraints; and
5. To identify and discus different methods of storage to prevent/control Spoilage Related Fungi in cocoyam during storage.

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1.5 Significance of 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).

This study will be of immense benefit to other researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.

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1.6 Scope of Study

The scope of the research is focused on the Isolation and Characterization of Spoilage Related Fungi in Colocasia Esculenta (Cocoyam).

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1.7 Limitations of the Study

During the course of this study, there were some problems encountered which stood as limitations to the research work. Some of the limitations include:

1. Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
2. Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).