CHAPTER ONE
INTRODUCTION
BACKGROUND OF THE STUDY
Yams (Dioscorea species of family Dioscoreaceae) constitute a multi-species crop that is important for food, income and socio-cultural practices. The most dominant production and consumption zone for yams in the world is in West and Central Africa. Yam plays important roles in the nutritional, social, cultural, and economic life of the people in the yam belt of Africa. Nutritionally, yam is a major staple providing food for millions of people in the world. It is eaten in different forms as fufu, boiled, fried, and roasted (Aidoo, 2009). In Ghana, yam constitutes about 13% of household food budget in urban centers (Aidoo, Ohene-Yankyera, Marfo and Blaise, 2009). Economically, yam is important in the local commerce in West Africa and accounts for about 32% of farm income (Chukwu and Ikwelle, 2000). The crop serves as a major source of foreign exchange earnings and is used as raw materials for starch industries and pharmaceutical companies (Amanze, Agbo, Eke-Okoro and Njoku, 2011). As the leading exporter of yam in the world, yam exports contribute significant foreign exchange earnings to the Ghanaian economy (Ohene-Yankyera, Aidoo and Ohenewa-Tawiah, 2011).
        The entire production, processing and marketing chain of yam offers vast employment opportunities for millions of people. The supply of yam offers prospects for income generation due to the number of people involved and the value attached to it. The marketing system, which affects the prices received by farmers and those paid by buyers, has a profound impact on sustainable food security (FAO, 2003).
        Yams are members of the genus Dioscorea and belong to the family Dioscoreaceae. Yams are dioecious plants and produce tubers and bulbils (aerial tubers) of economic importance. The stems are viny, leaves are cordate or ovate, tubers mostly cylindrical and rich in
carbohydrate which make them suitable to be used as food (Mandal,2003). Tuber development is an evolutionary adaptation to a dry season, when leafy shoots die back and tubers become dormant (Purseglove,2002). During the evolution of the edible Dioscoreas, the thickening and lobbing of the ancestral rhizome gave way to a well developed tuber system (Burkill,2000). In most species, they are renewed and produced annually, while in others they are perennial. As crops, yams are harvested every season and replanted using tuber pieces to regenerate the plant. Unlike other tropical root and tuber crop species, once harvested, yams can be stored for 4-6 months in ambient tropical conditions without significant deterioration of their nutritional properties. Tubers are also often dried and later milled into flour for reconstituting as a stiff paste (fufu), which is highly appreciated in West
Africa.