Fungi associated with the spoilage of cocoyam (colocasia esculenta)

Thesis Overview

<p> </p><p><strong>INTRODUCTION</strong></p><p>Cocoyam <em>(Colocasia esculenta) </em>is widely cultivate and used for food in Nigeria, Ghana and other countries including China. China and Ghana leading in world production (Onwueme and Charles, 1994).</p><p>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% (Agboola, 1979). In Nigeria, <em>Colocasia species</em>&nbsp;are the most important food and the third most important root/tuber crop after yams and cassava (Onwueme, 1978). 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 (cecil, 1992).</p><p>Cocoyams have very short post harvest storage life of a few days to weeks (Gollifer and Boot, 1973, Ugwunwanyi and Obeta, 1997). 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, (Onwueme and Charles, 1994),</p><p>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 (Ogundana et al;1970, Snowdon, 1991). Invasion by pathogens either through natural openings or wounds is considered the most critical factor in cocoyam spoilage (Degras, 1993).</p><p>A wide range of micro-organisms (Particularly moulds) have been associated with cocoyam decay, relatively few are implicated as primarily pathogens (Aderiye and Ogundana, 1984). 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. (Nwufo and Atu, 1987). Under these storage conditions, the fungi which are liable to attack cocoyam include; <em>Fusarium solani, Botryodiplodia, theobromae, Rhizopus, stolonifer, Aspergillus niger, Sclerotium roltsii, Trichoderma hamatum </em>and<em>&nbsp;Pythium </em>species. (Nwufo, 1980,Uwgunwanyi and Obeta, 1996). 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.</p><p>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, (Passam, 1982, and Onwueme, 1987). 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).</p><p>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).</p><p>Large quantities of carbohydrate-rich solid waste are produced in the course of processing cormels into starch and this constitute a waste disposal problem, (Duru, 2000).</p><p>The changing economic, social, political and cultural values of the world have challenged all countries to efficiently use their resources.</p><p>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 &nbsp; root with attendant yield losses &gt; 90%. In contrast, fields observations by farmers revealed that the red cocoyam has a certain degree of field tolerance against the cocoyam root rot &nbsp; disease, (Tambong, 2000).</p> <br><p></p>