In Vitro Evaluation Of Selected Plant Extracts Against Phytophthora Colocasiae Racib. Causing Taro Leaf Blight (Tlb)

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

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