Bacterial Wilt Research Articles

Evaluation of Pepper (Capsicum spp.) Germplasm Collection for Bacterial Wilt (Ralstonia solanacearum) Resistance

This study was conducted to identify resistant pepper accessions against the destructive disease bacterial wilt (BW) caused by Ralstonia solanacearum. A total of 338 pepper (Capsicum species) germplasms collected from different countries and deposited in the National Agrobiodiversity Genebank, Rural Development Administration (RDA), Republic of Korea, were evaluated. The evaluated accessions comprise samples from five distinct species: Capsicum annuum (213), Capsicum baccatum (47), Capsicum chinense (45), Capsicum frutescens (31), and Capsicum chacoense (2). Disease severity scores were recorded over four consecutive weeks and showed an increase in severity from initial inoculation to the end of the evaluation period. A strong correlation was observed between week 1 and 2, as well as between week 3 and 4. Ten resistant pepper accessions were identified. All selected accessions consistently exhibited low disease scores ranging from 0 to 1 throughout the observation period. These accessions belong to C. chinense (2), C. annuum (6), C. chacoense (1), and C. frutescens (1). Accessions such as IT236738 (C. chinense) and IT283498 (C. chinense) were demonstrated to have high resistance, showing no symptoms over all four weeks. Other accessions belonging to C. annuum (IT247232 and IT236340) and C. chacoense (IT158713) maintained a disease score of 0 (no symptoms) for the first three consecutive weeks; however, they developed symptoms with a score of 1 in the fourth week. Other important characteristics of the resistant materials were evaluated, including carotenoids and fruit characteristics. These accessions have important traits beyond resistance to the destructive pepper disease. They will serve as promising resources for breeding resistant pepper varieties against BW to enhance productivity.

A Rapid Method for Screening Pathogen-Associated Molecular Pattern-Triggered Immunity-Intensifying Microbes.

PAMP-triggered immunity (PTI) is the first layer of plant defense response that occurs on the plant plasma membrane. Recently, the application of a rhizobacterium, Bacillus amyloliquefaciens strain PMB05, has been demonstrated to enhance flg22Pst- or harpin-triggered PTI response such as callose deposition. This PTI intensification by PMB05 further contributes to plant disease resistance to different bacterial diseases. Under the demand for rapid and large-scale screening, it has become critical to establish a non-staining technology to identify microbial strains that can enhance PTI responses. Firstly, we confirmed that the expression of the GSL5 gene, which is required for callose synthesis, can be enhanced by PMB05 during PTI activation triggered by flg22 or PopW (a harpin from Ralstonia solanacearum). The promoter region of the GSL5 gene was further cloned and fused to the coding sequence of gfp. The constructed fragments were used to generate transgenic Arabidopsis plants through a plant transformation vector. The transgenic lines of AtGSL5-GFP were obtained. The analysis was performed by infiltrating flg22Pst or PopW in one homozygous line, and the results exhibited that the green fluorescent signals were observed until after 8 h. In addition, the PopW-induced fluorescent signal was significantly enhanced in the co-treatment with PMB05 at 4 h after inoculation. Furthermore, by using AtGSL5-GFP to analyze 13 Bacillus spp. strains, the regulation of PopW-induced fluorescent signal was observed. And, the regulation of these fluorescent signals was similar to that performed by callose staining. More importantly, the Bacillus strains that enhance PopW-induced fluorescent signals would be more effective in reducing the occurrence of bacterial wilt. Taken together, the technique by using AtGSL5-GFP would be a promising platform to screen plant immunity-intensifying microbes to control bacterial wilt.

The synergistic effect of biosynthesized CuONPs and phage (ϕPB2) as a novel approach for controlling Ralstonia solanacearum

BackgroundAs a vital soil-borne pathogenic bacterium, Ralstonia solanacearum can cause wilt disease in multiple Solanaceae plants. Several phages, such as ϕPB2, could infect R. solanacearum acting as a potential biological control agent in soil. In addition, some nanoparticles, especially copper preparation, also showed high toxicity on R. solanacearum with low toxicity on plant. However, whether they can be administered in combination and how effective they are in inhibiting the plant disease caused by R. solanacearum is known very little.ResultsIn this work, the characterization of CuONPs using scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction ascertained the presence of CuONPs which were nanometer particle of 83 nm. Then it was found that combined application of CuONPs with phage (ϕPB2) was superior to that of ϕPB2 or CuONPs alone in controlling tobacco bacterial wilt, with the CuONPs (250 mg/mL) and phage (106 PFU/mL) ratio being the best, at 79.1%. The combination of CuONPs and ϕPB2 also showed no obvious toxicity on tobacco growth than control like single application of CuONPs or ϕPB2. Furthermore, the transcriptome changes of R. solanacearum analysis indicated that the combination application and single allocation of CuONPs could inhibit “biofilm formation”, molecular function, biological processes, cellular components, metabolic process, and so on. In addition, the combination application showed higher inhibition of motility and biofilm, and better enhancement of cell membrane permeability, protein leakage, MDA concentration, and enzyme activity of their respiratory chain dehydrogenase than single application of CuONPs or phage (ϕPB2). Transcriptomes analysis also supported that the addition of ϕPB2 enhanced the toxicity of CuONPs by influencing the ABC transporters and quorum sensing, metabolic processes, and cellular biosynthetic processes of R. solanacearum.ConclusionIn total, our work not only proposed a novel way to increase the bactericidal effect of nanomaterials by adding phage, but also discovered the influence, synergistic effects, and mechanisms, which is useful to design novel way to combat phytopathogenic bacteria in the complicated environment.Graphical abstract

Plant-induced bacterial gene silencing: a novel control method for bacterial wilt disease.

Ralstonia pseudosolanacearum, a notorious phytopathogen, is responsible for causing bacterial wilt, leading to significant economic losses globally in many crops within the Solanaceae family. Despite various cultural and chemical control strategies, managing bacterial wilt remains a substantial challenge. This study demonstrates, for the first time, the effective use of plant-induced bacterial gene silencing against R. pseudosolanacearum, facilitated by Tobacco rattle virus-mediated gene silencing, to control bacterial wilt symptoms in Nicotiana benthamiana. The methodology described in this study could be utilized to identify novel phytobacterial virulence factors through both forward and reverse genetic approaches. To validate plant-induced gene silencing, small RNA fractions extracted from plant exudates were employed to silence bacterial gene expression, as indicated by the reduction in the expression of GFP and virulence genes in R. pseudosolanacearum. Furthermore, treatment of human and plant pathogenic Gram-negative and Gram-positive bacteria with plant-generated small RNAs resulted in the silencing of target genes within 48 hours. Taken together, the results suggest that this technology could be applied under field conditions, offering precise, gene-based control of target bacterial pathogens while preserving the indigenous microbiota.

Fortifying Plant Armor: CESA3 Enhances Arabidopsis thaliana's Defense Against Bacterial Wilt Under Heat Stress.

Fortifying Plant Armor: CESA3 Enhances Arabidopsis thaliana's Defense Against Bacterial Wilt Under Heat Stress.

First report of bacterial wilt caused by Clavibacter michiganensis subsp. michiganensis affecting tomato in Iğdır

Tomato wilt disease caused by Clavibacter mihiganensis subsp. michiganensis (Cmm) is one of the most destructive tomato diseases and causes significant crop loss in both greenhouse and field tomato production areas worldwide. In this study, the presence of the causal agent of bacterial wilt disease in tomato plants was investigated in Aras Valley. Isolation was made from diseased plant samples and it was determined whether the strains were pathogenic by cellulase activity and HR test. The virulence, morphological and biochemical characteristics of the strains were determined. Strains that fatty acid methyl ester extraction, isolation and purification were performed were identified at species and subspecies level with % similarity index using gas chromatography system. The diagnosis was confirmed with the Biolog Gen III System and all strains were identified at the subspecies level with a % similarity index. As a result of this study, 57 strains were obtained in the isolation, and 39 of the strains were determined not to be pathogenic. Strain 18 was determined as the pathogen causing the most damage to tomato plants with 100 % disease severity. Strains were identified as Cmm at subspecies level with a similarity index of 71-87 % using gas chromatography system and 54-75 % similarity index with Biolog Gen III System. According to the heat map created, it was determined that the strains consisted of two main clusters. The presence of pathogen in Aras Valley was proved for the first time by this study.

The Isolation, Identification and Efficacy of Bacillus velezensis XF-8 in Tomato bacterial Wilt Control

The Isolation, Identification and Efficacy of Bacillus velezensis XF-8 in Tomato bacterial Wilt Control

Reshaping the Primary Cell Wall: Dual Effects on Plant Resistance to Ralstonia solanacearum and Heat Stress Response.

Temperature elevation drastically affects plant defense responses to Ralstonia solanacearum and inhibits the major source of resistance in Arabidopsis thaliana, which is mediated by the receptor pair RRS1-R/RPS4. In this study, we refined a previous genome-wide association (GWA) mapping analysis by using a local score approach and detected the primary cell wall CESA3 gene as a major gene involved in plant response toR. solanacearumat both 27°C and an elevated temperature, 30°C. We functionally validatedCESA3as a susceptibility gene involved in resistance toR. solanacearumat both 27 and 30°C through a reverse genetic approach. We provide evidence that thecesa3mre1mutant enhances resistance to bacterial disease and that resistance is associated with an alteration of root cell morphology conserved at elevated temperatures. However, even by forcing the entry of the bacterium to bypass the primary cell wall barrier, thecesa3mre1mutant still showed enhanced resistance toR. solanacearumwith delayed onset of bacterial wilt symptoms. We demonstrated that thecesa3mre1mutant had constitutive expression of the defense-related geneVSP1, which is upregulated at elevated temperatures, and that during infection, its expression level is maintained higher than in the wild-type Col-0. In conclusion, this study reveals that alteration of the primary cell wall by mutating the cellulose synthase subunit CESA3 contributes to enhanced resistanceto R. solanacearum,remaining effective under heat stress. We expect that these results will help to identify robust genetic sources of resistance toR. solanacearumin the context of global warming. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Identification and Characterization of Ralstonia solanacearum Species Complex from Ginger (Zingiber officinale) in Semarang Regency, Indonesia

The Ralstonia solanacearum species complex is a highly destructive plant pathogen with a remarkably broad range of hosts, and ongoing discoveries continue to expand its host list. In May 2023, a new type of bacterial wilt affecting ginger (Z. officinale) crops in Semarang Regency, Central Java was reported. Early symptoms included sudden withering of leaves in adult plants followed by complete wilting and darkening of the vasculature, ultimately leading to plant death. This research specifically investigates the spread of Ralstonia solanacearum Species Complex within ginger cultivation in Semarang Regency. Twenty bacterial isolates were collected from soil and diseased Z. officinale plants at twenty different locations. Physiological and biochemical analyses confirmed that the causative agent for Z. officinale bacterial wilt was Ralstonia solanacearum belonging to biovar 3 and 4. The study also revealed that the distribution of this pathogen remains focused in the Banyubiru and Sumowono sub-districts. These findings will enhance our understanding of how Ralstonia solanacearum Species Complex spreads among ginger crops and its impact on them.

Genome-wide identification and expression analysis of the U-box E3 ubiquitin ligase gene family related to bacterial wilt resistance in tobacco (Nicotiana tabacum L.) and eggplant (Solanum melongena L.).

The E3 enzyme in the UPS pathway is a crucial factor for inhibiting substrate specificity. In Solanaceae, the U-box E3 ubiquitin ligase has a complex relationship with plant growth and development, and plays a pivotal role in responding to various biotic and abiotic stresses. The analysis of the U-box gene family in Solanaceae and its expression profile under different stresses holds significant implications. A total of 116 tobacco NtU-boxs and 56 eggplant SmU-boxs were identified based on their respective genome sequences. Phylogenetic analysis of U-box genes in tobacco, eggplant, tomato, Arabidopsis, pepper, and potato revealed five distinct subgroups (I-V). Gene structure and protein motifs analysis found a high degree of conservation in both exon/intron organization and protein motifs among tobacco and eggplant U-box genes especially the members within the same subfamily. A total of 15 pairs of segmental duplication and 1 gene pair of tandem duplication were identified in tobacco based on the analysis of gene duplication events, while 10 pairs of segmental duplication in eggplant. It is speculated that segmental duplication events are the primary driver for the expansion of the U-box gene family in both tobacco and eggplant. The promoters of NtU-box and SmU-box genes contained cis-regulatory elements associated with cellular development, phytohormones, environment stress, and photoresponsive elements. Transcriptomic data analysis shows that the expression levels of the tobacco and eggplant U-box genes in different tissues and various abiotic stress conditions. Using cultivar Hongda of tobacco and cultivar Yanzhi of eggplant as materials, qRT-PCR analysis has revealed that 15 selected NtU-box genes and 8 SmU-box may play important roles in response to pathogen Ras invasion both in tobacco and eggplant.

Morphological and biochemical identification of Ralstonia solanacearum strains in ginger (Zingiber officinale Roscoe) wilt disease

The Ralstonia solanacearum Species Complex (RSSC) is a significant plant pathogen affecting various agricultural commodities, including ginger. Understanding the distribution and characteristics of RSSC in ginger plants is crucial for effective disease management. This study aims to determine the distribution of RSSC in ginger plants and identify the pathogen through morphological and biochemical characterization. The research was conducted in Banyubiru and Getasan districts, Semarang Regency, Indonesia. The study involved purposive sampling, isolation, and purification of isolates, followed by morphological characterization through observation and biochemical characterization using Gram staining with KOH, oxidase test, arginine activity test, hypersensitivity test, bacterial density calculation, Koch's postulates, and biovar characterization. Three isolates from Banyubiru displayed typical morphological characteristics of RSSC, including round, mucoid colonies with red centers and white edges on TZC medium, and rod-shaped bacterial cells. Biochemical characterization identified these isolates as RSSC strains biovar 3 and 4, capable of causing bacterial wilt in ginger plants. The study confirmed the presence of bacterial wilt in ginger in Banyubiru district. The findings reveal the spread of bacterial wilt caused by RSSC in ginger plants in Banyubiru, Semarang Regency. There is a need for measures to control the potential spread of RSSC in the surrounding host plant areas in Tlumpak Village, Banyubiru district.

Genome Sequence Resource of Bacillus velezensis Strain HC-5, Revealing Its Potential as a Native Biological Control Agent Against Ginger Bacterial Wilt

The Bacillus velezensis strain HC-5, isolated from rhizosphere soil of ginger, exhibits effective biocontrol activity against ginger bacterial wilt. However, its genomic information has remained unexplored. This study presents the complete genome sequence of B. velezensis HC-5. The genome spans 4,237,244 bp and consists of 4,258 genes, with a total GC content of 45.85%. The HC-5 genome comprises 4,058 coding genes, 86 transfer RNAs, 27 ribosomal RNAs (rRNAs), 19 small RNAs (sRNAs), 70 interspersed repeats, and 74 tandem repeats. Moreover, we identified 10 gene clusters responsible for the biosynthesis of antibiotic compounds and 28 two-component systems associated with the bacterium's environmental adaptability. This genome sequence of B. velezensis HC-5 enhances our understanding of its biocontrol mechanisms and supports its potential development as an effective biocontrol agent for managing bacterial wilt in ginger production. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Tomato bacterial wilt disease outbreaks are accompanied by an increase in soil antibiotic resistance

The presence of soil-borne disease obstacles and antibiotic resistance genes (ARGs) in soil leads to serious economic losses and health risks to humans. One area in need of attention is the evolution of ARGs as pathogenic soil gradually develops, which introduces uncertainty to the dynamic ability of conventional farming models to predict ARGs. Here, we investigated variations in tomato bacterial wilt disease accompanied by the resistome by metagenomic analysis in soils over 13 seasons of monoculture. The results showed that the abundance and diversity of ARGs and mobile genetic elements (MGEs) exhibited a significant and positive correlation with R. solanacearum. Furthermore, the binning approach indicated that fluoroquinolone (qepA), tetracycline (tetA), multidrug resistance genes (MDR, mdtA, acrB, mexB, mexE), and β-lactamases (ampC, blaGOB) carried by the pathogen itself were responsible for the increase in overall soil ARGs. The relationships between pathogens and related ARGs that might underlie the breakdown of soil ARGs were further studied in R. solanacearum invasion pot experiments. This study revealed the dynamics of soil ARGs as soil-borne diseases develop, indicating that these ecological trends can be anticipated. Overall, this study enhances our understanding of the factors driving ARGs in disease-causing soils.

Evaluation of Integrated Pest and Disease Management Combinations against Major Insect Pests and Diseases of Tomato in Tamil Nadu, India

Tomatoes are one of the predominant vegetable crops grown throughout the year in Tamil Nadu, India. Their perishable nature and resource-intensive cultivation make them susceptible to biotic stress. The damage caused by invasive insect pests, bacterial wilt during the rainy season, and viral diseases are major yield-limiting factors, and the farmers mostly depend on calendar-based insecticide applications for insect pest and disease management in tomatoes. The desired tomato hybrids grafted onto bacterial wilt-resistant eggplant rootstocks offer protection against bacterial wilt during the rainy season. The integrated pest and disease management (IPDM) practices consist of resistant grafted tomato seedlings (wild eggplant rootstocks EG 203 and TS 03), bioinoculants (Bacillus subtilis + Trichoderma asperellum + Purpureocillium lilacinum), pheromone traps (Phthorimaea absoluta and Helicoverpa armigera), botanicals (azadirachtin), microbial pesticides (Bacillus thuringiensis, Metarhizium anisopliae, and Beauveria bassiana), and bio-rationals, which were evaluated in four locations in two major tomato-growing tracts of Tamil Nadu. The results revealed that the treatment EG 203 eggplant rootstock-grafted tomato along with IPDM practices performed better across all experimental locations than the other treatment combinations viz., TS 03 eggplant rootstock-grafted tomato + IPDM, tomato + IPDM, grafted tomato + farmers’ practice and tomato + farmers’ practice. The EG 203-grafted tomato recorded a higher yield than the farmers’ practice with significantly superior biometric parameters. The treatment of EG 203-grafted tomato and IPDM practices can be adopted for safer tomato production by enabling a reduction in pesticide applications while enhancing productivity.

Electron beam induced mutation in Curcuma longa L. against bacterial wilt disease

Electron beam induced mutation in Curcuma longa L. against bacterial wilt disease

Trojan Horse virus delivering CRISPR-AsCas12f1 controls plant bacterial wilt caused by Ralstonia solanacearum.

Plant bacterial wilt caused by Ralstonia solanacearum results in huge losses. Accordingly, developing an effective control method for this disease is urgently required. Filamentous phages, which do not lyse host bacteria and exert minimal burden, offer a potential biocontrol solution. A filamentous phage RSCq that infects R. solanacearum was isolated in this study through genome mining. We constructed engineered filamentous phages based on RSCq by employing our proposed approach with wide applicability to non-model phages, enabling the exogenous genes delivery into bacterial cells. CRISPR-AsCas12f1 is a miniature class 2 type V-F CRISPR-Cas system. A CRISPR-AsCas12f1-based gene editing system that targets the key virulence regulator gene hrpB was developed, generating the engineered phage RSCqCRISPR-Cas. Similar to the Greek soldiers in the Trojan Horse, our findings demonstrated that the engineered phage-delivered CRISPR-Cas system could disarm the key "weapon," hrpB, of R. solanacearum, in medium and plants. Remarkably, pretreatment with RSCqCRISPR-Cas significantly controlled tobacco bacterial wilt, highlighting the potential of engineered filamentous phages as promising biocontrol agents against plant bacterial diseases.IMPORTANCEBacterial disease, one of the major plant diseases, causes huge food and economic losses. Phage therapy, an environmentally friendly control strategy, has been frequently reported in plant bacterial disease control. However, host specificity, sensitivity to ultraviolet light and certain conditions, and bacterial resistance to phage impede the widespread application of phage therapy in crop production. Filamentous phages, which do not lyse host bacteria and exert minimal burden, offer a potential solution to overcome the limitations of lytic phage biocontrol. This study developed a genetic engineering approach with wide applicability to non-model filamentous phages and proved the application possibility of engineered phage-based gene delivery in plant bacterial disease biocontrol for the first.

Siderophore interactions drive the ability of Pseudomonas spp. consortia to protect tomato against Ralstonia solanacearum.

The soil-borne bacterial pathogen Ralstonia solanacearum causes significant losses in Solanaceae crop production worldwide, including tomato, potato, and eggplant. To efficiently prevent outbreaks, it is essential to understand the complex interactions between pathogens and the microbiome. One promising mechanism for enhancing microbiome functionality is siderophore-mediated competition, which is shaped by the low iron availability in the rhizosphere. This study explores the critical role of iron competition in determining microbiome functionality and its potential for designing high-performance microbiome engineering strategies. We investigated the impact of siderophore-mediated interactions on the efficacy of Pseudomonas spp. consortia in suppressing R. solanacearum , both in vitro and in vivo. Our findings show that siderophore production significantly enhances the inhibitory effects of Pseudomonas strains on pathogen growth, while other metabolites are less effective under iron-limited conditions. Moreover, siderophores play a crucial role in shaping interactions within the consortia, ultimately determining the level of protection against bacterial wilt disease. This study highlights the key role of siderophores in mediating consortium interactions and their impact on tomato health. Our results also emphasize the limited efficacy of other secondary metabolites in iron-limited environments, underscoring the importance of siderophore-mediated competition in maintaining tomato health and suppressing disease.

Bacterial community in apparently healthy and asymptomatic Eucalyptus trees and those with symptoms of bacterial wilt

Bacterial community in apparently healthy and asymptomatic Eucalyptus trees and those with symptoms of bacterial wilt

First Report of bacterial wilt disease of banana caused by Klebsiella variicola in Malaysia.

In Malaysia, bananas (Musa spp.) are the second most cultivated fruit and the fourth most cultivated fruit in terms of export revenue. In October 2018, about 5.0 out of 6.6 hectares of a banana plantation located in Teluk Intan, Malaysia, was impacted by an outbreak of banana disease. The onset of bacterial wilt symptoms is characterized by initial leaf wilting, followed by the subsequent withering of the entire plant during later stages, fruit stalk and fruit pulp discoloration, fruit rotting, and pseudostem necrosis. The diseased banana's symptomatic pseudostems and fruit pulps were surface-sterilised in 70% ethanol for 30 s, followed by 2% NaClO for 3 min, rinsed three times in sterilised water, and cut into small pieces approximately 5 mm2 in size. The tissues were macerated in a sterilised 0.85% NaCl solution for 5 min, and the resulting suspension was streaked onto nutrient agar, followed by incubation at 28°C for 2 days. After incubation, bacterial colonies with five unique morphological characteristics were observed. Two colonies of each unique morphological type were randomly chosen and subjected to preliminary bacterial identification by 16S rRNA gene sequencing. Based on BLASTn analysis, the five unique morphological types of bacteria were preliminarily identified as Enterobacter cloacae, Citrobacter farmeri, Klebsiella variicola, Kosakonia radicincitans, and Phytobacter ursingii. Previous reports identified K. variicola and K. radicincitans as banana pathogens, but Malaysia has yet to report the former. The amplified partial 16S rDNA sequences of both K. variicola isolates (designated as UTAR-BC1 and UTAR-BC2; GenBank accession numbers: PP531448 and PP531460, respectively), which were chosen to be the focus of this study, exhibited complete similarity to each other and were 100% identical (1426/1426 identity and 1420/1420 identity, respectively) to K. variicola (CP026013.1). To verify the identity of the bacterial isolate, three housekeeping genes, namely, infB(PP538994), rpoB (PP538995), and gyrB (PP538996) of UTAR-BC1, were amplified, sequenced, and subjected to multilocus phylogenetic analysis via the neighbour-joining method (1,000 bootstrap values). Phylogenetic analysis revealed that UTAR-BC1 belongs to the K. variicola clade. A pathogenicity assay of UTAR-BC1 was conducted on 4-month-old healthy banana plantlets (cv. Nangka) using the pseudostem injection method (Tripathi et al., 2008). First, UTAR-BC1 was grown overnight in nutrient broth and then adjusted to 108 CFU/ml in a sterile 10 mM MgCl2 solution. A total volume of 100 µL of the bacterial suspension was injected into the pseudostem of five healthy banana plantlets via a syringe with a needle. Control plants were mock-inoculated with a sterile 10 mM MgCl2 solution. The experiments were replicated thrice and inoculated plants were maintained at room temperature with natural sunlight and humidity, which resembled the field conditions. Two months after inoculation, all of the UTAR-BC1 inoculated spots of banana plantlets showed severe necrosis, while the banana leaves showed symptoms of wilted appearance, whereas the control plants remained symptomless. The reisolated pathogen from 90% of the symptomatic pseudostems and leaf blades shares the same morphological and molecular features as UTAR-BC1, thus fulfilling Koch's postulates. Previously, K. variicola has been reported to be a banana pathogen causing rhizome rot in India (Loganathan et al., 2021), plantain soft rot in Haiti (Fulton et al. 2020), and sheath rot and bulb rot in China (Sun et al., 2023; Jiang et al., 2024). To the best of our knowledge, this is the first report of bacterial wilt disease in bananas attributed to K. variicola in Malaysia. This finding will facilitate the surveillance of K. variicola as an emerging pathogen in banana plants in this region, thereby safeguarding the country's food security and promoting socio-economic growth.

Revealing bacteriophage capabilities: pH and NaCl concentration effects on RSJ2 phage infectivity and stiffness

The urgent necessity of reducing pesticides in the agricultural sector compels us to explore alternative, environmentally friendly approaches for controlling pathogenic bacteria and crop diseases. The usage of bacterial viruses or bacteriophages (phages) to control pathogenic bacteria is still limited due to the lack of understanding of the factors influencing shelf life. We examined the effects of pH and NaCl on the storage buffers on the infectivity of the RSJ2 phage. The RSJ2 phage infects Ralstonia solanacearum, causing bacterial wilt disease in tomatoes. The buffer that retained the highest phage titer (63 % after two months) was at pH 8.3 and 0.5 M NaCl. pH and NaCl concentrations directly affected the phage particles. The phage stiffness was measured with the nanoindentation technique, and a correlation between the phage remaining titers and the stiffness was revealed. The average stiffness associated with the highest remaining titer was 0.07 N/m, which falls into the intermediate stiffness range. The results agree with the previous study on the C22 phage stiffness, revealing an association between intermediate stiffness and phage infectivity. Phage stiffness can become an attribute of phage metastability and can be used to predict the phage shelf life.