Identification, characterization and mechanisms of potential rhizobacterial strains for biological control of bacterial brown stripe and bacterial sheath rot of rice, growth promotion and abiotic stress resistance in rice

Table of Contents

Chapter 1

Introduction

Chapter 2

Literature review

2.1. Current Status and Challenges of Rice Production in China

2.3.1. Bacterial Brown sheath rot of rice

2.1.1.1. The pathogen (P. fuscovaginae) and its disease symptoms on rice

2.1.2. Bacterial brown stripe of rice

2.1.2.1. The pathogen (A. avenae subsp. avenae) and its symptoms on rice

2.1.3. Abiotic stress

2.2. Approaches to improve the health of rice plant

2.3. Plant growth-promoting rhizobacteria

2.3.1. Mechanisms involved in PGPR bioactivity

2.3.1.1. Antagonism against plant pathogen

2.3.1.1.1. Race for root colonization

2.3.1.1.2. Biofilm formation

2.3.1.1.3. Siderophores production

2.3.1.1.4. Antibiotic-mediated suppression

2.3.1.1.5. Lytic enzymes and other byproducts

2.3.1.1.6. Induced systemic resistance

2.3.1.2. Plant growth promotion

2.3.1.2.1. Free Nitrogen-Fixing

2.3.1.2.2. Phytohormone production and phosphate solubilization

Chapter 3

A novel rhizobacterium Bk7 for biological control of brown sheath rot of rice caused by Pseudomonas fuscovaginae and its mode of action

3.2. Introduction

3.3. Materials and methods

3.3.1. Isolation and culture conditions

3.3.2. Primary screening

3.3.3. Inhibitory activity of the rhizobacterial culture filtrates against P. fuscovaginae

3.3.4. Pot experiment

3.3.4.1. Seed treatment and plant growth condition

3.3.4.2. Pathogen inoculation

3.3.4.3. Data collection and analysis

3.3.4.4. Growth promotion efficacy (GPE)

3.3.5. Characterization of growth promoting traits

3.3.5.1. Indole acetic acid production

3.3.5.2. Phosphate solubilization

3.3.5.3. Siderophores production

3.3.5.4. Microtitre plate assay for biofilm formation

3.3.6. Mechanism of biological control activity

3.3.6.1. Nature of culture filtrates

3.3.6.2. Multiplex PCR assay for distribution of antimicrobial peptide markers

3.3.6.3. Gene expression analysis with real time quantitative PCR

3.3.7. Identification of selected bacterial strains

3.3.7.1. Fatty acid methyl esters (FAMEs) analysis

3.3.7.2. Sequence analysis for 16S rRNA gene

3.4. Results

3.4.1. Primary selection of antagonists

3.4.2. Extracellular metabolites efficacy

3.4.3. Pot experiment

3.4.3.1. Growth promotion efficacy

3.4.4. Characterization of plant growth promoting traits

3.4.5. Mechanism of biological control activity

3.4.5.1. Molecular nature of the antibacterial metabolites

3.4.5.2. Detection of lipopeptide biosynthetic gene markers

3.4.5.3. Quantitative expression of antimicrobial peptide coding genes

3.4.6. Identification of rhizobacterial strains

3.5. Discussion

Chapter 4

Characterizing the mode of action of Brevibacillus laterosporus B4 for control of bacterial brown strip of rice caused by A. avenae subsp. avenae RS-1

4.1. Abstract

4.2. Introduction

4.3. Materials and methods

4.3.1. Bacterial strains and chemicals used

4.3.2. In vitro inhibition assessment

4.3.3. Characterization of the nature of antibacterial metabolites

4.3.4. Pot experiment

4.3.5. Bactericidal mode of action

4.3.5.1. Biofilm formation assay and transmission electron microscopy

4.3.5.2. Recovery of pathogen and validation

4.3.5.3. RNA isolation and real-time quantitative PCR

4.3.6. Statistical analysis

4.4. Results

4.4.1. In vitro trials

4.4.2. Biological control of bacterial brown strip disease in rice

4.4.3. Mechanism of biological control

4.4.3.1. Molecular nature of the antibacterial metabolites

4.4.3.2. Inhibition of biofilm formation

4.4.3.3. Disruption of cell integrity in A. avenae subsp. avenae

4.4.3.4. Differential expression of virulence-related genes in response to biological control

4.5. Discussion

Chapter 5

Alleviation of cold and drought tolerance in rice by using consortium of chemical inducers and rhizobacterial strains

5.1. Abstract

5.2. Introduction

5.3. Materials and Methods

5.3.1. Bacterial strains and chemical inducers used

5.3.2. Preliminary screening

5.3.3. Compatibility trials

5.3.4. Synergistic effect on plant growth under cold/drought stresses

5.3.4.1. Measure of MDA, proline and chlorophyll contents

5.3.4.2. Enzyme assays

5.3.4.3. Analysis of gene expression by RT-qPCR

5.3.5. Statistical analysis

5.4. Results

5.4.1. Primary trials

5.4.2. Compatibility tests

5.4.3. Co-inoculation improved growth and stress tolerance in rice plants

5.4.3.1. Change in lipid peroxidation, electrolyte leakage and proline content

5.4.3.2. Bacterization enhanced leaf chlorophyll under drought and cold stresses

5.4.3.3. Enzyme activities

5.4.3.4. Co-inoculation treatment induced changes in plant gene expression

5.4.4. Data analysis

5.5. Discussion

Objectives & Research Themes

The main objective of this study is to isolate and characterize rhizobacteria from rice crops, evaluate their biocontrol efficacy against Acidovorax avenae subsp. avenae (bacterial brown stripe) and Pseudomonas fuscovaginae (brown sheath rot), and investigate the potential of these bacteria, alone or in consortia with chemical inducers, to promote rice growth and enhance tolerance to abiotic stressors like cold and drought.

• Isolation and characterization of potential PGPR strains from rice rhizospheres.
• Evaluation of biological control efficacy against major bacterial rice pathogens.
• Analysis of biocontrol mechanisms, including biofilm formation, antibiotic production, and gene regulation.
• Assessment of synergistic effects of rhizobacterial consortia and chemical inducers on plant abiotic stress tolerance.
• Molecular analysis of stress-responsive gene expression patterns in rice plants.

Excerpt from the Book

Summary of Chapters

Chapter 1: This introductory chapter discusses the necessity of plant disease control and the role of biological control as an alternative to synthetic pesticides in modern sustainable agriculture.

Chapter 2: This chapter reviews the current status and challenges of rice production in China, detailing major biotic threats such as brown sheath rot and bacterial brown stripe, as well as the importance of plant growth-promoting rhizobacteria (PGPR).

Chapter 3: This chapter describes the identification and characterization of Bacillus amyloliquefaciens strain Bk7, highlighting its biocontrol efficacy against Pseudomonas fuscovaginae and its various growth-promoting traits.

Chapter 4: This chapter focuses on the mode of action of Brevibacillus laterosporus B4 for the control of bacterial brown stripe of rice caused by A. avenae subsp. avenae.

Chapter 5: This final chapter explores the synergistic effects of consortia of rhizobacteria and chemical inducers on alleviating cold and drought stress tolerance in rice plants.

Keywords

Rhizobacteria, Biological control, Abiotic stress tolerance, Acidovorex avenae subsp. avenae, Pseudomonas fuscovaginae, Rice, Bioactivities related mechanisms, Induced systemic resistance, PGPR, Cold stress, Drought stress, Biofilm formation, Lipopeptides, Gene expression.

Frequently Asked Questions

What is the core focus of this research?

This research primarily investigates the biological control of two major bacterial diseases of rice—bacterial brown stripe and brown sheath rot—while also assessing how these biological agents and specific chemical inducers can enhance plant growth and tolerance to environmental stressors like cold and drought.

What are the primary target pathogens?

The two main pathogens studied are Acidovorax avenae subsp. avenae, which causes bacterial brown stripe, and Pseudomonas fuscovaginae, which causes brown sheath rot in rice.

What is the primary objective of the work?

The goal is to isolate and characterize rhizobacterial strains, evaluate their ability to suppress these specific pathogens, and determine if they can alleviate abiotic stresses in rice, thereby improving yield and sustainability in agricultural practices.

Which scientific methods are employed?

The research utilizes a variety of methods including isolation and in vitro screening of antagonistic bacteria, greenhouse pot experiments, molecular identification (16S rRNA analysis), multiplex PCR for antimicrobial gene marker detection, and real-time qPCR for analyzing gene expression patterns during stress responses.

What is covered in the main body of the work?

The work is divided into three major experimental chapters: Chapter 3 discusses Bacillus amyloliquefaciens strain Bk7 against brown sheath rot; Chapter 4 investigates Brevibacillus laterosporus B4 against bacterial brown stripe; and Chapter 5 explores how consortia of these bacteria and chemical inducers like SA and BABA alleviate cold and drought stress.

Which key terms describe this study?

Key terms include Rhizobacteria, Biological control, Abiotic stress tolerance, Acidovorax avenae, Pseudomonas fuscovaginae, PGPR, Induced systemic resistance, and Biofilm formation.

What is the identified biological mechanism for strain B4?

The study found that Brevibacillus laterosporus B4 acts by suppressing biofilm formation, disrupting cell membrane integrity, and down-regulating virulence-related genes in A. avenae subsp. avenae.

What role does the chemical consortium (BBSB) play?

The mixture termed "BBSB" (comprising two rhizobacterial strains plus SA and BABA) demonstrated a synergistic ability to enhance rice survival, maintain cell integrity, and modulate stress-responsive gene expression under both cold and drought conditions.