ABSTRACT
Investigations were conducted to determine the qualitative and quantitative phytohemical properties of methanolic and aqueous leaf extracts of Chromolaena odorata L., Carica papaya L.,and Ocimum gratissimum L.using standard methods. The results revealed that alkaloids, saponins, flavonoids, glycosides, reducing sugars, carbohydrates, steroids, tannins and terpenoids were present in all the test plants. However, methanolic leaf extract of C. odorata had the highest amounts of saponins, flavonoids and steroids and lowest tannins content. Carica papaya had highest content of alkaloids, carbohydrates and terpenoids and lowest content of glycosides, reducing sugars and steroids, while O. gratissimum had highest composition of glycosides, reducing sugars and tannins and lowest composition of alkaloids, saponins, flavonoids, carbohydrates and terpenoids. Comparisons on the aqueous leaf extracts of the test plants showed that C. odorata had the highest composition of glycosides and tannins and lowest composition of saponins, flavonoids and steroids. Carica papaya had the highest amounts of flavonoids and terpenoids and lowest composition of alkaloids, glycosides, carbohydrates and tannins, while O. gratissimum had the highest contents of alkaloids, saponins, reducing sugars, carbohydrates and steroids, and lowest composition of terpenoids. The compositions of the leaf extracts were significantly different at P ≤ 0.05. The significance of the test p lants and the importance of these phytochemicals were discussed with respect to the roles they play in plant disease control.
CHAPTER ONE
1.0 INTRODUCTION
A large number of chemicals have been developed for the control of plant diseases, but due to the growing awareness of the hazardous side effects of these chemicals, more emphasis is given to the use of biocontrol agents. One of the major challenges in the field of Plant Pathology is the need for some ecofriendly and safe alternative control strategies for agriculture, which has led researchers to turn their attention to plant extracts as sources of biocontrol agents. Therefore, growing of most plants and tress now goes beyond afforestation purposes to making them available and accessible for exploitation for their natural chemical composition vis-Ã -vis their usefulness in the management and cure of both plant and animal diseases. These chemical compounds, known also as phytochemicals, provide defenses for the plants against diseases and other environmental factors. It is now evident that most of these plant chemicals could also be helpful in the treatment of both animal and human diseases. These phytochemicals which are bioactive include alkaloids, flavonoids, steroids, saponin, tannins, terpenoids, glycosides and other phenolic compounds classified as most important (Edeoga et al., 2006). Most of these phytochemicals are used in the control of animal and plant diseases for their rich composition, which provides both preventive and curative properties.
The use chemicals has helped increase yield obtained but one of the major problems of the constant use of chemicals is the development of resistance in the target organisms. Studies in the use of plant extracts for the control of plant diseases have shown the importance of natural chemicals as a natural source of non-phytotoxic and easily biodegradable alternative fungicides and antibiotics (Akueshi et al., 2002).
Fungal diseases of plants destroy 10-30% of the total yield of crops and in some perishable fruits and tubers especially in developing countries; they destroy more than 30% of the crop yield (Kader, 2002). The quality of Irish potato is adversely affected by post-harvest handling, packaging and transportation which result in decay by microorganisms which become activated because of the changing physiological state of the produce (Agrios, 2005). Among the prevalent diseases recorded and the increased use of plants in areas of disease control has raised concerns about the side effects of agrochemicals (Kader, 2002).
1.1 JUSTIFICATION FOR THE STUDY
Fungi are the most prevalent pathogens affecting a wide range of host plants. This is often facilitated by colonization of wounded and exposed plant tissues which in turn bring about destruction and losses of economically important food crops. The ease of spoilage (especially after harvest) of plant produce could be attributed to improper storage, transportation, handling and marketing as acknowledged by the international monitoring world food resources unit (Weber, 2003). In view of these losses, man has resorted to the use of agrochemicals (biocides) in his agricultural practices despite the great justified alarm of their hazards. Attempts to control plant diseases with chemical preservatives or the use of gamma radiation are either too sophisticated or costly for an average farmer in West Africa. In addition, the ultimate aim of maintaining good ecological relationship is often downplayed. Therefore, to counter the problems associated with the use of agrochemicals, the use of chemicals of plant origin (phytochemicals) was suggested as an alternative method of plant disease control (Amadioha, 2000; 2002).
