Isolation and characterization of PGPR from the rhizopheres of selected vegetables in Ogun state

ABSTRACT

Beneficial bacteria that colonize the root of plants and are capable of stimulating the growth of plants directly or indirectly are called plant-growth promoting rhizobacteria. The objective of this study was to isolate and characterize plant-growth promoting rhizobacteria from the rhizosphere of some selected vegetables collected at different locations in Ago-iwoye, Oru and Ijebu-Igbo in Ijebu-North local Government Area of Ogun state, using general microbiological and biochemical tests. Invitro screening was done for three different plant growth promoting activities i.e. indole acetic acid production, ammonia production and catalase. The physicochemical properties; pH, organic matter, organic carbon, available phosphorus and cation exchange capacity of the samples were analysed. The total viable bacteria counts of the rhizobacteria ranged from 10.0x106 cfu/g to 43.0x106cfu/g with Lagos spinach having the least bacterial counts and tree spinach having the highest bacterial count. A total of twenty-nine bacteria belonging to eleven different genera were isolated and are Bacillus sp, Staphylococcus sp, Aeromonas sp, Proteus sp, Acinetobacter sp, Achromobacter sp, Acetobacter sp, Azospirillum sp, Klebsiella sp, Peptostreptococcus sp and Pseudomonas sp. Thirteen isolates belonging to six different genera were positive for IAA production and are Bacillus sp, Staphylococcus sp, Aeromonas sp, Proteus sp, Acetobacter sp and Azospirillum sp. Twenty-nine isolates produced catalase while all the isolates produced ammonia. These plant growth promoting abilities exhibited by the isolates make them suitable for use in further investigation in pot and field experiments of vegetable plants. 

CERTIFICATION

This is to certify that this project was carried out by OLUSOGA, Tolulope Mary with Matric No: 11092489 in the Department of Microbiology, Faculty of Science, Olabisi Onabanjo University, Ago-Iwoye under my supervision.

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          Supervisor

 Dr. (Mrs) O. A. F Ilusanya                                                                                      Date

 B.Sc. (Ogun), M.Sc. (Ibadan)

 Ph.D. (O.O.U.)

DEDICATION

  I dedicate this report to Almighty God, for His protection, guidance, graces conferred on me seen and unseen throughout my training and to my parents, Mr and Mrs K.M Olusoga for their unending sacrifice and parental support.

ACKNOWLEGDEMENT

My profound appreciation goes to God Almighty.

It also goes genuinely to my supervisor Dr.Mrs.O.A.F Ilusanya, thank you for your listening ears, patience, kindness, directives and supervision on my research.

My appreciation also goes to my parents, Mr. and Mrs. K.M. Olusoga for their support, love, care, unending sacrifice, from my childhood till this moment, to all my siblings, Segun, Ade and Victor, also to my uncles, aunts and my entire family members.

I say a big thank you to my group members, Olutayo, Tola and Jide for their unfettered commitments towards the success of this project.

TABLE OF CONTENTS

Title pagei                                                                                     Abstract                                                                                      ii

Certificationiii                                                                                 Dedication            iv                                                                                           

Acknowledgementv                                                                            

Table of Contentsvi                                                                             

List of tables ix                                                                                    

List of figurex

CHAPTER ONE 

INTRODUCTION           1

CHAPTER TWO: LITERATURE REVIEW

2.1 Vegetables 5

2.2 Rhizosphere        6

2.3 Physicochemical Properties of soil7

2.3.1 Soil Ph8

2.3.2 Nitrogen8

2.3.3 Available Phosphorus8

2.4 Plant Growth-Promoting Rhizobacteria (PGPR)  9

2.3.1 Bacillus  10

2.3.2 Pseudomonas 11

2.3.3 Acetobacter  12

2.3.4 Azotobacter12

 2.3.5 Rhizobium13

2.3.6 Azospirillum13

2.4 Mechanism of plant growth promotion14

2.4.1 Direct mechanism15

2.4.2 Indirect mechanism15

2.5 PGPR as plant growth enhancement15

2.6 Plant growth promoting attributes of PGPR15

2.6.1 Biological Nitrogen Fixation15

2.6.2 Phosphate solubilization16

2.6.3 Phytohormone production16

2.6.4 Siderophore production17

2.6.5 Hydrogen cyanide production18

                                                                            

CHAPTER THREE: MATERIALS AND METHOD

3.1 Materials19

3.2 Collection of soil samples 19

3.3 Physicochemical analysis of soil samples19

3.4 Microbiological analysis22

3.4.1 Isolation of rhizobacteria22

3.4.2 Total viable count and pure culture23

3.4.3 Preparation of stock culture23

3.4.4 Identification and characterization of  rhizobacteria isolates23

3.4.4.1 Gram staining23

3.4.5 Biochemical tests24

3.4.6 Plant-growth promoting traits27

CHAPTER FOUR

Results29

CHAPTER FIVE

Discussion and Conclusion41

References44

LIST OF TABLES

Table 1: Rhizobacterial count of soil samples from some selected vegetables31

Table 2: Physicochemical analysis of soil samples32

Table 3: Morphological and Biochemical characteristics of rhizobacteria in 

    soil samples33

Table 4: Plant growth promoting traits of isolates36

LIST OF FIGURES

Figure 1 : Pie chart showing the percentage of occurrence of rhizobacteria39

Figure 2: Plant growth promoting abilities of the isolated bacteria 40