CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND OF THE STUDY

Sweet potato, Ipomoea batatas (L) Lam, is a dicotyledonous plant which belongs to the family Convolvulaceae. It has approximately 50 genera and more than 1,000 species of this family. Ipomoea batatas is the only crop plant whose large, starchy, sweet tasting tuberous is an important roots vegetable (Purseglove, 1991; Woolfe, 1992). The young leaves and shoots are sometimes eaten as green vegetable. Sweet potato is distantly related to the Irish potato, Solanum tuberosum. It is commonly confused with yam in some parts of North America, although they are only very distantly related to other tubers known as yams (in the discoreaceae family), which is native of Africa and Asia. Sweet potatoes are native to the tropica parts of South America and were domesticated there at about 8,000 and 6,000 BC ago (Austin, 1988). The primary centre of diversity occurs in Columbia, Ecuador and Northern Peru while secondary centre were found in Central America (Yen, 1982).

Sweet potato was introduced to Europe by Columbus. The movement of sweet potato to Africa and Asia was accomplished by the Spanish and the Portuguese people who introduced them to their trading settlements. Sweet potato cultivars are grouped into various classes, namely: firm, dry mealy flesh (preferred in most countries of South East Asia, the pacific and East Africa); soft, moist gelatinous flesh (preferred in developed countries); and coarse, fibrous tubers for industrial uses as starch, snack foods, alcohol and animal feed (Onwueme, 1978).

Ipomoea batatas plant has a creeping stem above the ground called a “stolon” with the leaves arranged spirally on the stem. The leaves are simple and may have entire margins or may be digitally lobed. The flowers are regular with bell-shaped corolla and are solitary. The petiole varies in colour from green to purple which can be 5 – 30cm long and retains the ability to grow in a curved or twisted manner so as to expose the lamina to maximum light (IITA, 1982 and Yen, 1982).

Neem, Azadirachta indica (A. Juss) is a member of the mahogany family. Neem trees are attractive broad – leaved evergreens that can grow up to 30m tall and 2.5m in girth. Their spreading branches form rounded crowns as much as 20m across. They remain every green except during extreme drought, when the leaves may fall off. The short, usually straight trunk has a moderately thick, strongly furrowed bark. The roots penetrate the soil deeply; at least where the site permit, and particularly when injured, they produce suckers. This suckering tends to be especially prolific in dry locations. Neem secretes Azadirachtin which repel or reduce the feeding of many insects on crops (Stoll, 1986).

1.2 STATEMENT OF THE PROBLEM

Neem usually is easy to establish; it grows best on deep, well-drained sandy soils. It can be raised in nurseries and transplanted as seedlings but direct sowing on the sites is sometimes easier and more successful. Neem is also renowned for good growth on dry, infertile sites. It performs better than most tress where soils are sterile, stony and shallow, or where there is a hardpan near the surface. The tree also grows well on some acid soils. Indeed, it is said that the fallen neem leaves, which are slightly alkaline (PH 89.2), are good for neutralizing acidity in the soil. On the other hand, neem cannot stand “wet feet” and it quickly dies when site becomes water-logged. Control of diseases and pests of sweet potato comes in diverse forms as most of them will not be sufficient on their own (Jacobson, 1987). To produce a good potato crop, a combination of various control methods is often applied. One of the first active ingredients isolated from neem, azadirachtin, has proved to be the tree’s main agent for battling insect pests. It appears to cause up to 90 percent of effective control on most pests. It does not kill insects – at least not immediately. Instead, it both repels and disrupts their growth and reproduction. Research over the past 20 years has shown that it is one of the most potent growth regulators and feeding deterrents ever assayed. It will repel or reduce the feeding of many species of insect pests as well as some nematodes. In fact, it is so potent that a mere trace of its presence prevents some insects from even touching plants (Jacobson, 1986b). This argument thus formed the technical basis for considering neem as an agent on managing insect pests in sweet potato cultivation.

1.3 AIM AND OBJECTIVES ODF THE STUDY

The main aim of the research work is to examine antifungal activities of azadiracta indica on fungal infected sweet potato. The specific objectives of the study are:

1. to determine the types of fungal affecting sweet potato
2. to determine the importance of azadiracta indica (neem plant) to sweet potato
3. to determine the pharmacological actions of azadiracta indica (neem plant) on sweet potato
4. to examine the phytochemistry of azadiracta indica (neem plant) and  sweet potato

1.4 RESEARCH QUESTIONS

The study came up with research questions so as to ascertain the above stated objectives of the study. The research questions for the study are:

1. What are the types of fungal affecting sweet potato?
2. What is the importance of azadiracta indica (neem plant) to sweet potato?
3. What are the pharmacological actions of azadiracta indica (neem plant) on sweet potato?
4. What is the phytochemistry of azadiracta indica (neem plant) and sweet potato?

1.5 SIGNIFICANCE OF THE STUDY

The study on antifungal activities of azadiracta indica on fungal infected sweet potato will be of immense benefit to the food science and technology department in Nigeria. The study will explore azadiracta indica and their role in the preservation fungal infected sweet potato. The study will also serve as a repository of information to other researchers that desire to carry out similar research on the above topic. Finally the study will contribute to the body of the existing literature on antifungal activities of azadiracta indica on fungal infected sweet potato

1.6 SCOPE OF THE STUDY

The study will cover on antifungal activities of azadiracta indica on fungal infected sweet potato