Response Of Spk 004 To Meloidogyne Species Infestation And Impact Of Sweet Potato Management Practices On Nematofauna In Mwea, Kenya

TABLE OF CONTENTS

DECLARATION................................................................................................................ i

DEDICATION................................................................................................................... ii

ACKNOWLEDGEMENT ............................................................................................... iii

LIST OF TABLES .......................................................................................................... vii

LIST OF FIGURES ....................................................................................................... viii

LIST OF ABBREVIATIONS AND ACRONYMS .........................................................x

GENERAL ABSTRACT ................................................................................................ xii

CHAPTER ONE ................................................................................................................1

INTRODUCTION..............................................................................................................1

1.1 Background information ............................................................................................1

1.2 Statement of the problem ...........................................................................................3

1.3 Justification ................................................................................................................4

1.4 Research questions .....................................................................................................5

1.5 Objectives of the study ...............................................................................................5

1.5.1 General objective ................................................................................................5

1.5.2 Specific objectives ..............................................................................................5

CHAPTER TWO ...............................................................................................................6

LITERATURE REVIEW .................................................................................................6

2.1 Sweet potato production and importance ...................................................................6

2.2 Sweet potato production constraints ..........................................................................7

2.2.1 Plant parasitic nematodes associated with sweet potato .....................................7

2.3 Management of plant parasitic nematodes .................................................................9

2.3.1 Plant resistance in the management of root-knot nematodes (RKN) ..................9

2.3.2 Management of other plant parasitic nematodes ..............................................10

2.4 Free-living nematodes ..............................................................................................14

2.4.1 Organic amendments and their effect on free-living nematodes ......................14

CHAPTER THREE .........................................................................................................16

3.0 Abstract ....................................................................................................................16

3.1 Introduction ..............................................................................................................17

3.2 Materials and methods .............................................................................................18

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3.2.1 Experimental site ..............................................................................................18

3.2.2 Experimental design and planting .....................................................................19

3.2.3 Soil sampling ....................................................................................................20

3.2.4 Analysis of soil properties and weather data collection ....................................20

3.2.5 Collection of plant root samples and determination of dry matter content .......20

3.2.6 Assessment of sweet potato yield .....................................................................21

3.2.7 Nematode extraction and identification ............................................................21

3.2.8 Statistical analysis .............................................................................................21

3.3 Results ......................................................................................................................22

3.3.1 Soil chemical and physical properties...............................................................22

3.3.2. Rainfall and temperature during the study period ............................................22

3.3.3. Performance of sweet potato cultivar SPK 004 under field conditions ...........23

3.4 Discussion ................................................................................................................24

3.5 Conclusion ................................................................................................................27

CHAPTER FOUR ............................................................................................................28

4.0 Abstract ....................................................................................................................28

4.1 Introduction ..............................................................................................................29

4.2 Materials and methods .............................................................................................31

4.2.1 Experimental site ..............................................................................................31

4.2.2 Experimental design..........................................................................................31

4.2.3 Soil sampling ....................................................................................................31

4.2.4 Nematode extraction and identification ............................................................32

4.2.5 Analysis of soil properties and weather data collection ....................................32

4.2.6 Data analysis .....................................................................................................32

4.3 Results ......................................................................................................................34

4.3.1 Soil properties and weather data .......................................................................34

4.3.2 Effects of different treatments on the relative abundance in nematode communities ................................................................................................................34

4.3.3 Effect of different treatments on nematode communities over time.................39

4.3.4 Effects of treatments on the diversity of nematode species ..............................42

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4.3.5 Effects of treatments on ecological, soil food web indices and metabolic footprints .....................................................................................................................43

4.4 Discussion ................................................................................................................48

4.5 Conclusion ................................................................................................................53

CHAPTER FIVE .............................................................................................................54

5.0 Abstract ....................................................................................................................54

5.1 Introduction ..............................................................................................................55

5.2 Materials and methods .............................................................................................56

5.2.1 Plant material and treatments ............................................................................56

5.2.2 Collection of soil samples .................................................................................56

5.2.3 Nematode extraction and identification ............................................................56

5.2.4 Data analysis .....................................................................................................57

5.3 Results ......................................................................................................................57

5.3.1 Soil properties and data on rainfall and temperature ........................................57

5.3.2 Population dynamics and diversity of free-living nematodes under management practices .................................................................................................57

5.4 Discussion ................................................................................................................61

5.5 Conclusion ................................................................................................................62

CHAPTER SIX ................................................................................................................63

SYNTHESIS .....................................................................................................................63

6.0 General Overview ....................................................................................................63

6.1 Conclusions ..............................................................................................................65

6.2 Recommendations ....................................................................................................66

REFERENCES .................................................................................................................