ABSTRACT

This study was conducted to examine the In vitro antifungal activity of leaf ethanol extracts of Azadirachta indica, Senna alata, Eucalyptus camaldulensis and Tithonia diversifolia against Phytophthora colocasiae Racib. Extracts were tested against isolated pure culture of P. colocasiae at 5, 10 and 20mg/ml. 3mg/ml Ridomil and untreated culture served as the standard and absolute control respectively. Experiment was conducted in a completely Randomized Design (CRD) and all treatments were replicated thrice. Data were subjected to analysis of variance (ANOVA) using statistical package for social scientists (SPSS). Means were separated by Duncan Multiple Range Test (DMRT) and test of significance at 5%. Results indicated that 20mg/ml extracts of A. indica and 3mg/ml of Ridomil had the best percentage radial growth inhibition of P. colocasiae at 100%, followed by S. alata (78.19%) at 5mg/ml while extract of E. camaldulensis showed the lowest anti-fungal activity at 5mg/ml (19.33%). P. colocasiae growth in absolute control was un-inhibited (0.00%). Mycelia dry weight of P. colocasiae at 10mg/ml of E. camaldulensis was recorded at 0.10±0.61g contrary to 0.00g recorded against other plant extracts. At 20mg/ml, A. indica supported a mycelia dry weight of 0.09±0.06g but none was recorded against other plant extracts. Ridomil did not support mycelia growth in PDB while absolute control had a significant (p≤0.05) mycelia dry weight of 0.27±0.08g. Leaf extract of A. indica should be characterized to obtain the pure active component responsible for anti-fungal activity and used for further studies in the control of the pathogen in the field.

TABLE OF CONTENTS

Cover page            

 Title page i

 Declaration ii   

Certification iii 

Dedication iv                                                                   

Acknowledgements v              

Table of Contents vi                  

List of Figures viii                    

List of Plates ix   

  Abstract x

CHAPTER ONE 1

INTRODUCTION               1

Statement of problem   6

Justification of study   7

Aims and objectives   8

CHAPTER TWO   9

2.0. LITERATURE REVIEW   9     

2.1. History of taro (Colocasiae esculenta)   9                                                                    

2.2. Taro leaf blight (TLB) (Phytophthora colocasiae Raciborski) 10                            

 2.3. Symptoms of taro leaf blight                                                                          11       

2.4. Temperature requirement of P. colocasiae                                                  12     

 2.5. Management of P. colocasiae                                                                       13                     

2.5.1. Cultural control 13

 2.5.2. Biological control                                                                                              14    

2.5.3.   Chemical control                                                                                              15               

 2.6. Efficacy of plant extracts on Phytophthora colocasiae 17

CHAPTER THREE 19

3.0. MATERIALS AND METHODS 19                        

3.1 Source of plant materials                                                                                 19            

 3.2. Study area                                         19               

 3.3. Experimental design              19              

   3.4. Preparation of plant extracts 19                 

  3.5. Preparation of media              20                      

3.6 Isolation of pathogen from diseased taro leaf tissues              20                         

3.7 Pathogenecity test 21

 3.8. Experimental procedure  22                  

3.9.      Inoculation and measurement of radial growth              22                   

 3.10.    Measurement of the mycelia dry weight 23

CHAPTER FOUR 24

4.0. RESULTS AND DISCUSSION 24                                                                                             4.1 Results              24                

 4.2 Discussion 31

CHAPTER FIVE

5.0 CONCLUSION AND RECOMMENDATIONS 36          

 5.1 Conclusion 36                

   5.2 Recommendations            37

REFERENCES 38

APPENDIX 43