Abstract

Yam is one of the most abundant and preferred staple foods in West Africa.  However, its availability is affected by rate of deterioration arising from poor postharvest handling such as lack of storage facilities.The major problems in yam tuber storage are sprouting, respiration and transpiration, which cause weight and quality losses.

This study investigated the effect of two treatments (sand and sawdust) and two storage methods (barn and pit) on the shelf life of white yam (Dioscorearotundata) tubers within a period of   three months. A total of 36 freshly harvested yamtubers were cured by storing inside canvas of tarpaulin for five days. The cured tubers were stored in barn and pit each containing 5kg of sawdust and 2kg of sand.The parameters taken to assess their performance were tuber weight loss,rotting, sprouting and pest infestation after   3 months of storage.

The weight loss and sprouted tubers were measured once per two weeks for 3months.Results revealed that, the weight loss of the treated tubers were not significantly different (P>0.05) when compare to that of the control withinthreemonths. However, at week six sawdust experienced the least weight loss compare to control and sand.  There was a significant lower (p < 0.05) sprouting rate in both storage conditions for T1(contol) during the 3rd week of storage when compare to T3(sand) and T2(sawdust) whereas at the sixth week of storage, the sprouting rate was significantly lower (p < 0.05) for T3(sand) when compare to T1(control) and T2(sawdust).

This implies that storage with sawdust and sand  could bepartially used to extend their shelf life of yam with respect to weigh loss and sprouting.

CHAPTER ONE

INTRODUCTION

1.1. Background of the study

Yams areperennial or annual tuber-producing vine, belonging to the genus Dioscorea(family Dioscoreaceae) with about 600 species (Obenet al., 2016). The crop is an important staple for millions of people in tropical and subtropicalareas of Africa, Asia, South America, and the Caribbean and Pacific Islands (Adisaet al., 2015; Ngo-Ngwe et al., 2014).

Yam is most important in the “yam zone” of West Africa which covers the tropical and subtropical regions of Côte d’Ivoire, Ghana, Togo, Benin, Nigeria and Cameroon (Obenet al., 2016) where over 67.3 million metric tons (MT) (92.2%) of the world’s estimated 73 million metric tons (MT) of yams are produced yearly (FAO, 2017). Nigeria stands out as the highest producer with 47.9 million MT (65.7%) of the world’s production, while Cameroon with an annual production of 648,407 MT (0.9%), and is ranked sixth in the West African yam zone and seventh in the world, behind Togo.

On an annual base, yams are cultivated in Cameroon on a surface area of 57512 ha; with an average yield of 11.3 MT/ha (FAO, 2017). Globally, there are 10 main cultivated yam species, originating from tropical areas of Africa, South East Asia and South America. These include D. alataL (Asiatic or water yam), D. esculenta (Lour) (Chinese yam), D.oppositeThunb, and D. japonica Thunb from Asia; D.nummulariaLam, D. pentaphylla L. from Asia and Oceania; D. rotundataPoir (White guinea yam), trifoliate yam commonly called Sweet yam:D.dumetorum(Kunth) Pax  and D. cayenensisLam (Yellow guinea yam) from West Africa; D. trifidaL. (Cush-cush yam) from South America; and D. bulbiferaL.from Africa and Asia (Coursey, 1976; Lyonga, 1976; Dansiet al., 2013). Water yam is the most diversified and widely distributed species while White guinea yam has the world’s highest production level. Among the yam species, D. alata, D. cayenensis and D. rotundataare most economically important in the west African yam zone (Dansiet al., 2013), while in Cameroon D. alata, D.cayenensis, D. dumetorum, D. rotundataare the mostimportant species, cultivated in all agro – ecological zonesof the country (Ngo-Ngwe et al., 2014).

Despite its importance, yam production and productivity have been limited by a range of constraints including unavailability and high cost of seed yams, high demands of labor, pre- and post-harvest pests, inadequate storage facilities, various diseases and institutional research neglect of the crop.

Yam is an annual crop, so for it to be available throughout the year, harvested tubers must be stored for six to eight months before new yams are harvested. The possibility to store fresh yam tubers is decisively influenced by their dormancy which occurs shortly after their physiological maturity (wilting point). During the storage period, a substantial amount of yam is lost. Postharvest food losses are one of the major causes of food insecurity in Africa. According to AMCOST (2006), pre- and post-harvest food crop loss among African countries is estimated at about 10%, which is higher than the global average. Although it has been difficult to quantify post-harvest storage losses, some claim that as much as 20% of yam tubers may be lost to pest attack in storage (FAO 2005).

Causes of storage losses of yam tubers include: sprouting, transpiration, respiration,rot due to mould and bacteriosis, insects, nematodes and mammals (Passamet al., 1978). Harvested tubers are frequently attacked by several viruses, bacteria, fungi and insects. Also,rodents feed on some of the harvested tubers stored in the barns (Igbeka, 1985) Sprouting,transpiration and respiration are physiological activities which depend on the storageenvironment mainly temperature and relative humidity (Passamet al., 1978). These physiologicalchanges affect the internal composition of the tuber and result in destruction of ediblematerial, which under normal storage conditions can often reach 10% after 3 months,and up to 25% after 5 months of storage (Passamet al., 1978).

To minimize post-harvest losses, improved methods of storage such as the use of healthy and sound tubers, proper curing if possible combined with fungicide treatment, adequate ventilation to remove heat generated by respiration of sprouts and rotted tubers that develop (Jill et al., 1980). Monitoring the presence of rodents and protection from direct sunlight and rain is also necessary.

Yams can be best stored in cool, dry and ventilated conditions (Umogbai, 2013). Yam storage structures come in different shapes and sizes depending on the ability of the farmer, locality and cultural practices. The construction materials are usually wood, ropes, palm fronds, guinea corn stalks, and mud (FAO, 2004; Umogbai and Satimehin, 2004). According to Opara (1999), there are several traditional low-cost storage methods and structures for yam tubers; the most common of them include leaving the tubers in the ground until it is needed, storing under tree shades, yam barns, and underground structures such as pits, ditches and mud structures. Umogbaiet al. (2013) and Onemoleaseet al. (2009) also reported that there are well ventilated weather-proof, insect and rodent proof strong shelters for storage of yam tubers; unfortunately, the cost of these structures discourages farmers, who are the major producers of yams, from adopting such improved storage.

Storage in sand and sawdust is a post-harvestpractice whereby tubers areplace inside the storage facilities with sand or sawdustsprinkle for about 2 days prior to storage.

The usage of sand and sawdust do not completely prevent deterioration but slow down the rate of deterioration thereby increasing the shelf life of yam.

However, the use of sand and sawdust during storage is rarely practiced by farmers in Cameroon, so there is therefore the need to promote less expensive, improved storage structures using local materials for smallholder yam farmers. This approach will not only increase the incomes of yam producers but also ensure an all-year-round availability of yams, which is critical in achieving sustainable food security in the country. This research focuses on the use of sand and sawdust to extend the shelf life of white yam (Dioscorearotundata) withinBuea municipality.

1.2. Problem statement

Most developing countries such as Cameroon continue to rely on the agriculturalsector for economic growth, poverty alleviation, food security andenvironmental sustainability (Nuryartono et al, 2005). However, mostdomestic products, including yam go waste as they travel along the chain fromthe farm gate to the final consumer. Post-harvest losses of yam are one of themajor challenges confronting yam farmers in Cameroon.

Furthermore, ineffective postharvest handling of yam constitutes a major source of loss to local farmers and yam producers in Cameroon who engage in production and marketing of tubers. The environment within their storage facilities is not also suitable for the long-term storage of yam. A number of treatments and techniques have been developed to reduce these physiological activities and also to protect the tubers from post harvest diseases. These include treatment with palm wine, plant extracts and gamma irradiation; storage techniques used include cold storage, improved underground storage and improved yam barn (Zinash, 2008). However, only very few studies have used sand and sawdust treatments as well as   pit and barn to extend the shelf life and maintain the quality ofwhite yam tubers (Dioscorearotundata).Fresh yams are difficult to store and are subject to post harvest losses during storage (Afoakwa and Sefa-Dedeh, 2001). Eradication or reduction of post harvest losses is therefore important to bring increasing food security and reduce suffering of local farmers.

1.3. Objective

The general objective of the study was to determine the shelf life of yam tubers stored in sawdust and sand in the Bueamunicipality.

1.3.1.   Specific objectives

1. To assess the weight loss of white yam (Dioscorearotundata)that stored in sawdust and sand.
2. To determine the rate of deterioration of tubers store in sawdust and in sand

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