근권미생물을 활용한 유묘썩음병 및 키다리병의 생물학적 방제 = Biological control of bacterial seedling rot and bakanae disease using rhizobacteria

다국어 초록 (Multilingual Abstract)

Bacterial grain rot (BGR) and bacterial seedling rot (BSR) of rice, caused by Burkholderia glumae, is one of the most significant bacterial diseases affecting rice (Oryzae sativa L.) production worldwide. Infected seeds show varying symptoms depending on the severity of infection. Severe infection can lead to seed decay and failure to germinate, while mild infection often results in coleoptile browning, poor seedling growth, and eventual seedling death. When the disease occurs on panicles, characteristic brown stripes and grain discoloration develop, which serve as diagnostic indicators of BGR. In severe cases, embryo development is inhibited, resulting in empty grains. Since the first report of BGR in Fukuoka, Japan in 1955, the disease has spread globally, including to Korea, Japan, the United states, and southeast Asia. It has become a major threat to rice cultivation, particularly in tropical and subtropical regions, where it is regarded as a high-risk bacterial disease causing serious crop losses.
Bakanae disease, caused by Gibberella fujikuroi is another major disease of rice. Infected seedlings typically show abnormal elongation with weak growth, resulting in poor stand establishment and yield losses. Because the pathogen is readily transmitted via contaminated seeds, effective and safe seed stage management is essential for reducing disease incidence under field conditions. The disease compromises stand establishment and seedling vigor and can ultimately reduce productivity; reported yield losses vary markedly with region and cultivar, ranging from 3.0% to 95.4%, with historical reports of 20–50% loss in Japan and 15–26% loss in parts of India.
Chemical control has been the primary strategy for managing this disease; however, the indiscriminate use of chemical bactericides has raised concerns regarding human and animal health, environmental safety, and the emergence of bactericide-resistant strains. Consequently, interest in environmentally friendly biological control agents has significantly increased as an alternative approach to managing seed-borne diseases in rice.
In this study, I evaluated the potential of biocontrol agents against the seed-borne pathogen B. glumae, the causal agent of bacterial seedling rot in rice. Various antagonistic bacterial strains were isolated from soil, and their antagonistic activity and plant growth-promoting effects were assessed. Although Burkholderia pyrrocinia JBC226 and Cytobacillus firmus JBRS159 did not exhibit direct antibacterial activity against B. glumae, they produced siderophores, proteases, and indole-3-acetic acid (IAA), demonstrating plant growth-promoting (PGP) effects in both Arabidopsis thaliana and rice. Moreover, the two strains showed no antagonistic interaction with each other, suggesting the potential for use as a combination. When rice seeds infected with B. glumae were treated with a suspension of the combination of JBC226 and JBRS159 at a controlled concentration, a control efficacy of 67.2% was observed. Furthermore, the co-application of a silicon compound with the mixed culture enhanced the control efficacy against both bacterial grain rot and bakanae disease in rice seeds. Additionally, Bacillus velezensis JBCS608, selected in this study, exhibited strong antagonistic activity not only against B. glumae but also against various other bacterial and fungal pathogens that cause severe diseases in rice. JBCS608 also produced siderophores and IAA, promoting plant growth in both arabidopsis and rice. When infected seeds were treated with a JBCS608 suspension, control efficacies of 66.7% and 55.0% were achieved, demonstrating its potential as a biocontrol agent.
To enhance the practical application and commercialization potential of JBCS608, a bioformulation was developed. After inducing sporulation of JBCS608, both wettable powder and liquid formulations were prepared, and their control efficacies were compared with vegetative cell suspensions. The results showed comparable disease control efficacy, while the storage stability significantly improved, maintaining viability for up to 6 months.
Based on these results, the combination of JBC226 and JBRS159 with silicon compounds, as well as JBCS608, demonstrated effective control of the BGR and bakanae disease. These treatments not only exhibited biocontrol efficacy but also promoted plant growth, indicating high potential as biofertilizers. Furthermore, the bioformulation developed using JBCS608 proved to be a practical and commercially applicable biocontrol product.

목차 (Table of Contents)

• CHAPTER 1. Screening and characterization of strains with biocontrol activity against seed-borne diseases 1
• ABSTRACT 2
• 1.1 INTRODUCTION 3
• 1.2 MATERIAL AND METHODS 6
• 1.2.1 Antibacterial activity against major bacterial pathogens of rice 6
• 1.2.2 Antifungal activity against major bacterial pathogens of rice 6
• 1.2.3 Preparation of B. glumae infected rice seeds 7
• 1.2.4 Biocontrol of bacterial seedling rot 7
• 1.2.5 Plant growth promoting effects on A. thaliana 8
• 1.2.6 Siderophore production 8
• 1.2.7 Phosphate solubilization 9
• 1.2.8 Protease production 9
• 1.2.9 IAA production 9
• 1.2.10 Effects of hormone pathway inhibitors on the growth of A. thaliana treated with selected strains 10
• 1.2.11 Growth promoting assay of A. thaliana signaling mutant 10
• 1.3 RESULTS 12
• 1.3.2 Plant growth promoting effect in A. thaliana 15
• 1.3.3 Biocontrol efficacy 15
• 1.3.4 Phosphate solubilization 17
• 1.3.5 Protease production 17
• 1.3.7 Effect of selected strains on hormone signaling inhibitors on growth promotion of A. thaliana 19
• 1.3.8 Effect of selected strains on the growth of hormone signaling mutant A. thaliana 21
• 1.4 DISCUSSION 23
• 1.5 REFERENCE 26
• CHAPTER 2. Biological control of bacterial seedling rot and bakanae disease using combination of Burkholderia pyrrocinia JBC226, Cytobacillus firmus JBRS159 with silicon compound 30
• ABSTRACT 31
• 2.1 INTRODUCTION 32
• 2.2 MATERIAL AND METHODS 35
• 2.2.1 Compatibility of JBC226 and JBRS159 35
• 2.2.2 Preparation of BSR infected rice seeds 35
• 2.2.3 Biocontrol efficacy of selected strains at different concentrations 35
• 2.2.4 Control of BSR by JBC226, JBRS159 and combination 36
• 2.2.5 Preparation of G. fujikuroi infected seeds and evaluation of biocontrol efficacy 37
• 2.2.6 Rice growth promoting effects of JBC226, JBRS159 and combination 37
• 2.2.7 Biocontrol efficacy against BSR by co-application of strains and silicon compound 38
• 2.2.8 Biocontrol efficacy against bakanae disease by co-application of strains and silicon compounds 38
• 2.2.9 PGP effects in A. thaliana by co-application of strains and silicon compounds 39
• 2.2.10 Generation of antibiotic-resistant strains 39
• 2.2.11 Root colonization assay on rice seeds 40
• 2.3 RESULTS 41
• 2.3.1 Compatibility between JBC226 and JBRS159 41
• 2.3.2 Biocontrol efficacy of selected strains at different inoculum concentrations 42
• 2.3.3 Biocontrol efficacy of BCA 45
• 2.3.4 Biocontrol efficacy of bakanae disease 48
• 2.3.5 Rice growth promoting effects of the selected strains 50
• 2.3.6 Biocontrol efficacy against BSR by co-application of strains and silicon compounds 52
• 2.3.7 Biocontrol efficacy against bakanae disease by co-application of strains and silicon compounds 55
• 2.3.8 PGP effects in A. thaliana by co-application of strains and silicon compounds 57
• 2.3.9 Survival and colonization of strains of rice roots 59
• 2.4 DISCUSSION 60
• 2.5 REFERENCE 63
• CHAPTER 3. Biological control and formulation of bacterial grain rot and bakanae disease in rice using Bacillus velezensis JBCS608 68
• ABSTRACT 69
• 3.1 INTRODUCTION 70
• 3.2 MATERIAL AND METHODS 72
• 3.2.1 Preparation of BSR infected seeds 72
• 3.2.2 Seed treatment with JBCS608 72
• 3.2.3 Biocontrol efficacy of JBCS608 at different concentrations 72
• 3.2.4 Biocontrol assay against BSR 72
• 3.2.5 Preparation of G. fujikuroi infected seeds and evaluation of biocontrol efficacy 73
• 3.2.6 Endospore formation 73
• 3.2.7 Development and preparation of wettable powder formulation 74
• 3.2.8 Preparation of liquid formulation 74
• 3.2.9 Biocontrol efficacy against BSR using WP and Lq formulations 75
• 3.2.10 Storage stability of WP and Lq formulations 76
• 3.2.11 Effect of JBCS608 on rice growth 76
• 3.2.12 Generation of antibiotic-resistant mutant strain 76
• 3.2.13 Colonization assay in rice rhizosphere 77
• 3.3 RESULTS 78
• 3.3.1 Biocontrol efficacy of JBCS608 at different concentrations 78
• 3.3.2 Biocontrol efficacy of JBCS608 against BSR 81
• 3.3.3 Biocontrol efficacy against bakanae disease 84
• 3.3.5 Development of WP and Lq formulation 87
• 3.3.7 Storage stability of WP and Lq formulations 92
• 3.3.8 Colonization of JBCS608 on rice root 94
• 3.4 DISCUSSION 96
• 3.5 REFERENCE 101