CHAPTER ONE
INTRODUCTION
1.1 Background of study
Sweet potato (Ipomoeabatatas (L) lam) is grown in more than 100 countries in tropical, subtropical and temperate climate. It ranks as the world’s seventh most important crop, with an estimated annual production of approximately 122 million metric tons
Sweet potato is a major staple food in African, Asia the Caribbean and South America, where they are important sources of carbohydrate, vitaminA and C, fiber, iron,potassium and protein (Wolfe, 1992).
Sweet potato belongs to the family convolvulaceae and originated from South America from where it was introduced to usually consider the only species of Ipomoea of economic important. In developing countries, sweet potato is especially valued because it is highly adaptable and tolerates high temperate, low fertility soil and drought.Sweet potato is also used as animal feed, which has been a byproduct of crops grown for human consumption. It is the only crop among the root tuber crops that had a position per capita annual rate of increase in production in sub-Saharan Africa.
Increasing recognition of the great potential of the sweet potato crop as a nutritious food for humans and animals has resulted in intensified research efforts to enhance production and consumption in recent decades (Woolf, 1992, Yamakawa and Yoshimoto, 2002).The plant is an herbaceous perennial vine, being alternate heart-shaped or palmately lobed leaves and medium-sized sympetalous flowers.
The edible tuberous root is long and tapered, with a smooth skin whose colour ranges between yellow, orange,red, brown purple and beige. Its flesh ranges from beige through white, red pink,violet,yellow,orange and purple.
I.batatas is propagated vegatatively as the seeds are heterogeneous and used only for breeding purposes.In tropical countries where the crop can be grown year-round, the crop is usually propagated by replanting vine cuttings from the preview crops. In temperate countries, the crop is usually grown in a nursery for field transplantation at the beginning of the summer.
The origin and domestication of sweet potato is through to be in CentralAmerica, however,some generally agree that it originated in North America where many more varieties are found there.
Research to identify accessions high in different nutritional qualities(dry matter,protein,starch,sucrose,B-carotene,Fe,Zn,Ca and Mg ) has been initiated by the
center for international potato(CIP), for germplasm in gene bank and breeding
Sweet potato in relation to other crops has nutritional potentials and is endowed with such medicinal properties, like antioxidant activities for healthy living.Antioxidants are substance or nutrients present in our food which can increase cellular defense and help prevent oxidative damage to cellular component of our body for maintaining health andpreventing disease, such as cancer and heart disease (Mervat and Hanan, 2009). In addition to many other uses in medicine and industrial field, it is used in manufacturing cosmetics, for food preservation and colorant. Yamakawa (2001) reported that the synthetic antioxidants have restricted use in food, as they are suspected to be carcinogenic. The searching for and exploiting natural antioxidant very important and such demand is high now as reported by Ames(1983). While antioxidant is a class of plant secondary metabolite, the plant kingdom still offers vast array of valuable natural polyphenolic compounds, several isolated plant constituents, as well as crude extracts of vegetables and fruits; which have been recognized to possess beneficial effects against free radicals in biological system as antioxidant.
In recent time, ideas have shifted from seeing sweet potato as a crop with high calories to other veritable nutritional potential such as B-carotene, which have anti-
oxidative properties. Access to sweet potato varieties with such qualities will not only boost the nutrition of the consumers but also position it as a global stable food.
1.2 Justification
Apart from identifying varieties with good morpho-agronomic characteristics such as leaf biomass, good tuber yield which are rich in nutrient, there is need to understand the yield quality and antioxidant properties as well as the stability of the nutrient traits across diverse environments, toguide future choice and use of appropriate breeding strategies for the improvement of sweet potato such as understanding would also allow making informed choice regarding which cultivar or potatoes to be used in breeding efforts for improved nutrients varieties and new sweet potato population.
Antioxidants are nutrient present in our food which can increase cellular defense and prevent disease, such as cancer and heart disease. In addition to this, uses in medicine and industrial field, making of cosmetics, preservation of food. Research has shown that the synthetic antioxidant have restricted use in food, as they are suspected to be carcinogenic.
Ideas have shifted from seeing sweet potato as a crop with high calories to other veritable nutritional potential such as B-carotene, which is a precursor of vitamin A and polyphenolic compound, which have antioxidative properties.
Access to sweet potato varieties with such qualities will not only boost the nutrition of the consumers but also position it as a global staple food. Consequently, evaluating and stabilizing theseyield, quality and antioxidant properties of sweet potatoes becomes indigestible.
