Current Situation of Fire Blight in China

A novel gliding filamentous bacterium Herpetosiphon tianshanensis sp. nov. NSE202 is a promising biocontrol agent for fire blight

BACKGROUND

Fire blight (Erwinia amylovora), a devastating bacterial disease, has posed significant challenges to apple and pear production for more than a century. In recent years, the spread of fire blight to China via Xinjiang has heightened concerns among planters and government authorities, particularly given the region's distinct geography and climate, underscoring the urgent need for innovative biocontrol strategies.

RESULTS

This study introduced a predatory bacterium, Herpetosiphon tianshanensis sp. nov. NSE202, isolated from natural forest soil in Xinjiang, China, that could be a new type of promising biological control agent for the management of fire blight. Strain NSE202 differs from the five other reported Herpetosiphon species in terms of its physiological characteristics and genomic composition. Using morphological, 16S ribosomal RNA gene and whole-genome analysis, the NSE202 strain was assigned to H. tianshanensis sp. nov. Strain NSE202 demonstrated strong predatory capability against Erwinia amylovora (Ea) in vitro. The biocontrol capacity of NSE202 was assayed on isolated inflorescences of fragrant pear and biennial potted pear seedlings under greenhouse conditions. The protective control efficacy of NSE202 was 64.8% in the inflorescences assay. Bacterial spraying of NSE202 significantly reduced the incidence and disease index on pear seedlings with protective and therapeutic control efficacies of 71.9% and 61.5%, respectively. Strain NSE202 demonstrated stable colonization on pear blossoms and twigs under greenhouse conditions. The pathogen population was suppressed significantly in planta treated with NSE202, as shown by colony counts on plates, scanning electron microscopy, and quantitative polymerase chain reaction analysis. Further investigation demonstrated that secondary metabolites of strain NSE202, collected via macroporous resin, and extracellular proteins, precipitated using ammonium sulfate, had pronounced lytic activity against the fire blight pathogen. In addition, certain lipases, glycoside hydrolases, and peptidases secreted by strain NSE202 may contribute significantly to the predation process. These findings suggest that such components may serve as promising biocontrol factors.

CONCLUSIONS

The discovery of H. tianshanensis sp. nov. NSE202 provides a new and promising strategy for combating fire blight. The isolates' multiple capacities to colonize and exert antagonistic effects against Erwinia amylovora makes them highly promising candidates for an integrated biological solution. © 2025 Society of Chemical Industry.

Evaluation of the Efficacy of Three Antagonistic Bacteria Strains in the Management of Fire Blight

Fire blight, caused by Erwinia amylovora, poses a significant threat to the sustainable development of the Korla Xiangli (Pyrus×sinkiangensis. Yu) industry. In this study, we used multiple experimental approaches to comprehensively evaluate the efficacy of three antagonistic bacterial strains-namely, Mg-7 (Leuconostoc mesenteroides), Rt-10 (Alcaligenes faecalis), and Rt-11 (Bacillus siamensis)-in controlling fire blight. In vitro plate inhibition assays revealed that Mg-7 exhibited the largest inhibition zone diameter, exceeding Rt-10 and Rt-11 in this respect, suggesting its strong antifungal potential. In therapeutic tests conducted on detached leaves, Mg-7 achieved the highest control efficiency, 60.39%, while Rt-10 demonstrated the greatest efficiency (76.96%) in protective tests. Conversely, in therapeutic trials focusing on detached branches, Mg-7 showed a control efficiency of 45.90%, whereas Rt-11 exhibited the highest efficiency, 86.27%, in protective trials. Furthermore, in vitro evaluations indicated that the Mg-7 treatment significantly reduced the lesion spread area. Enzymatic analyses revealed that, in the leaf protection assay, catalase activity (CAT) demonstrated significant increases of 65.56%, 85.46%, and 45.55% under the Mg-7, RT-10, and RT-11 treatments, respectively, when compared with the EA control group on day four. Correspondingly, in the branch protection assay, polyphenol oxidase (PPO) activity displayed marked elevations of 62.84%, 52.06%, and 82.69% under identical experimental conditions at the same time point. These treatments not only upregulated antioxidant enzyme activities but also significantly reduced malondialdehyde (MDA) content, effectively mitigating oxidative damage while enhancing foliar and branch resistance to fire blight infection. Field trials conducted in outdoor orchards confirmed that the Mg-7 bacterial suspension provided more effective and stable control against fire blight than Rt-10 and Rt-11. Overall, Mg-7 shows significant potential for use as a biocontrol agent for managing fire blight because of its high efficacy, stability, and ability to enhance plant defense responses.

Comparative transcriptome analysis and candidate gene mining for fire blight of Pear resistance in Korla fragrant Pear (Pyrus sinkiangensis Yü)

Fire blight of pear is caused by Erwinia amylovora, which can cause devastating damage to pear trees and other pome fruit trees worldwide. Fire blight has resulted in a reduction in the production of Korla fragrant pears in Xinjiang, China, as well as a decrease in their quality and taste, causing severe economic losses. To this end, a comparative transcriptome analysis of common Korla fragrant pear (KFP, susceptible) and a bud mutation line (1910, resistant) at three inoculation periods was conducted. Clustering and principal component analysis (PCA) of the RNA-seq data revealed that the differences between lines were greater than those within lines. A total of 7271 DEGs were identified in the bud mutation line, while 11,937 DEGs were identified in KFP. Between KFP and the resistant material bud mutation line, 11,937 DEGs were identified, which were significantly enriched in the pathways of photosynthesis, jasmonic acid metabolic process, flavonoid biosynthesis, and starch and sucrose metabolism. A total of 8 clusters were identified for all (17,354) DEGs via k-means, and KEGG pathway annotations were performed for each individual cluster. In addition, the 1027 differentially expressed transcription factors (TFs) were clustered into five clusters, and the TFs with the largest fold change in each cluster were identified. A gene coexpression network was further constructed through weighted correlation network analysis (WGCNA), and 15 key genes that determine the fire blight resistance of Korla fragrant pear were identified. These research results provide a theoretical basis for a deeper understanding of the molecular mechanism of Korla fragrant pear resistance to fire blight and provide new genetic resources for the study of Korla fragrant pear resistance to fire blight.

First report of fire blight on Cotoneaster in China

In May 2023, characteristic symptoms of fire blight, suspected to be caused by Erwinia amylovora, were observed infected wild Cotoneaster plants in the secondary forest along the lower reaches of the Jilgilang River, Xinjiang, China. Symptomatic tissues were collected, and bacterial isolation and purification were performed. The bacterium was identified through morphological characterization of the colonies, pathogenicity assays, tobacco hypersensitivity tests, and specific polymerase chain reaction (PCR) amplification, followed by sequence analysis. The isolated bacterium exhibited morphological features consistent with E. amylovora, and pathogenicity tests conducted under greenhouse conditions confirmed its pathogenicity, as evidenced by bacterial dissemination from the main leaf veins to surrounding tissues and the presence of bacterial exudates at the petioles. Furthermore, a pronounced hypersensitive response was observed in tobacco. PCR followed by sequencing revealed over 99.6% similarity with E. amylovora plasmid pEa29 repeat region. These findings confirm the E. amylovora is the causal agent of the fire blight disease in wild Cotoneaster plants. This is the first documented case of the fire blight affecting Cotoneaster plants in China. The detection of this pathogen has significant implications for the conservation of wild Rosaceae germplasm in the Tianshan Mountains wild fruit forests in Xinjiang.

Identification of Streptomycin-Resistant Erwinia amylovora in Iowa

Erwinia amylovora is a bacterial pathogen that causes fire blight, an important disease in apples and pears. Applying the antibiotic streptomycin during the phenological bloom stage is considered the most effective management tactic for fire blight. Although streptomycin-resistant (SmR) E. amylovora populations have emerged in major U.S. apple-producing regions, antibiotic resistance data for medium- to small-sized apple-producing regions such as the Midwest are still lacking. This Short Communication article collected symptomatic fire blight samples from Iowa apple orchards during 2022 and 2023, where recent fire blight outbreaks persisted despite streptomycin use. Among E. amylovora isolates from seven counties in Central and Eastern Iowa, approximately 90% of them were SmR. All SmR isolates exhibited a single base pair mutation in codon 43 of the rpsL gene, conferring resistance to streptomycin levels exceeding 1,000 μg/ml. Through clustered regularly interspaced short palindromic repeat (CRISPR) analysis, we characterized two E. amylovora genotypes unique to our region. Whole genome sequencing of one representative SmR isolate, IA01, confirmed its CRISPR genotype, and subsequent phylogenetic analysis suggested that IA01 is genetically similar to Michigan isolates and distinct from those in eastern and western regions of North America. Furthermore, the disease-causing ability of IA01 was comparable to that of the highly virulent Ea110 strain, a streptomycin-sensitive strain isolated from Michigan, in immature pears. Overall, this study underscores the urgent need for regional strategies to address antibiotic resistance and provides insights into its genetic basis and geographic distribution, which are crucial for sustainable orchard management.

Manipulation of juvenile hormone signaling by the fire blight pathogen Erwinia amylovora mediates fecundity enhancement of pear psylla

BACKGROUND

In nature, plant pathogens often rely on insect vectors for transmission. Through long-term evolution, plant pathogens and insect vectors have established a mutually beneficial symbiotic relationship. Fire blight, caused by the Gram-negative bacterium Erwinia amylovora (Eam), poses a significant global threat to apple and pear production due to its rapid dissemination among host plants of the Rosaceae family. Despite evidence of E. amylovora transmission by various insects, the association between this pathogen and the pear psylla Cacopsylla chinensis, a common vector insect in pear orchards, remains unclear.

RESULTS

Sampling investigations and qRT-PCR results revealed that C. chinensis, from 11 pear orchards severely affected by fire blight disease in Xinjiang of China, harbored varying levels of this pathogen. Eam-positive females exhibited significantly higher fecundity compared to Eam-negative individuals, displaying accelerated ovarian development and a notable increase in egg production. Further RNAi results revealed that juvenile hormone (JH) receptor methoprene-tolerant (CcMet) and a crucial downstream gene Krüppel-homologue 1 (CcKr-h1) mediated the fecundity improvement of C. chinensis induced by Eam. Additionally, miR-2b, which targets CcKr-h1, was identified as being involved in Eam-induced fecundity enhancement in C. chinensis.

CONCLUSION

This study unveils, for the first time, that Eam colonize and amplify the fecundity of C. chinensis females. Host miR-2b targets CcKr-h1 of the JH signaling pathway to regulate the heightened fecundity of C. chinensis induced by Eam. These findings not only broaden our understanding of the interaction between plant pathogens and insect vectors, but also provide novel strategies for managing fire blight and pear psylla. © 2024 Society of Chemical Industry.

Whole genome sequence data of Erwinia amilovora strain E22, from Kazakhstan

Erwinia amilovora is the causative agent of bacterial blight of rosaceae plants. The disease affects ornamental species of this family and fruit trees of great economic importance, such as apple and pear. In the presented research, sequencing of the Erwinia amilovora strain E22 isolated in Kazakhstan, was performed on the Illumina MiSeq platform, followed by bioinformatics processing and gene annotation using SPAdes, RAST, antiSMASH and CARD programs and databases. The size of the assembled genome is 3,799,623 bp. Annotation of the Erwinia amilovora genome assembly identified 3462 genes, including 3251 protein-coding genes and 117 RNA genes. This genome will be helpful to further understand the evolution of Erwinia amilovora and can be useful for obtaining control agents.

Morphomolecular characterization of invasive fruit borer infesting apple

Apple, a vital fruit crop worldwide and a major crop grown in northern parts of India, acts as a backbone for the survival and livelihood of the farming community. However, it is prone to severe damage from insect pests and diseases. In the past few years, due to erratic weather patterns, there has been an alarmingly increased infestation of different insect pests, both invasive and non-invasive, resulting in substantial economic losses to this industry. One similar case was seen in the Himalayan region of India, where the apple crop in Karewas was heavily damaged by some invasive fruit borer, feeding on pulp and making galleries to reach the seed locules, thereby destroying the seed material. To ascertain the true identity of this pest, a study based on morpho-molecular characterization of this pest was carried out in the Faculty of Agriculture, Wadura, SKUAST Kashmir, India, during the years 2021 and 2022. The invasive fruit samples were collected from apple orchards at different locations (experimental sites) in North India by installing delta sticky traps @ 5 traps/ha for moth collection. The fruit-boring larvae and pupa were also collected and reared in confined chambers of the laboratory with controlled temperature and humidity. All the laboratory investigations were conducted at the Division of Entomology, FoA, Wadura, SKUAST Kashmir. During the investigation, it was confirmed that the invasive borer is a codling moth (Cydia pomonella L.), a member of the family Tortricidae, order Lepidoptera, which was earlier having quarantine importance in India, as it was only present in the Ladakh region of India. From the phylogenetic analysis of sample sequences, the species of codling moth present at all experimental sites was more identical to the codling moth sequence from Leh (the northernmost arid region), India. Further, the study of life cycle and voltinism revealed that codling moth completes three generations per year in Kashmir, with a single cycle lasting up to 2.5 months. However, the timing of various generations varies, depending on prevailing weather conditions at specific locations and times. The number of generations completed by codling moth in Kashmir conditions during apple growing season was three full and a half overwintering generations. The study of the life cycle of this important pest was necessary to know the weak link for its effective management and to prevent the economic loss in apple fruit.

Discovery and characterization of a novel pathogen Erwinia pyri sp. nov. associated with pear dieback: taxonomic insights and genomic analysis

In 2022, a novel disease similar to pear fire blight was found in a pear orchard in Zhangye City, Gansu Province, China. The disease mainly damages the branches, leaves, and fruits of the plant. To identify the pathogen, tissue isolation and pathogenicity testing (inoculating the potential pathogen on healthy plant tissues) were conducted. Furthermore, a comprehensive analysis encompassing the pathogen's morphological, physiological, and biochemical characteristics and whole-genome sequencing was conducted. The results showed that among the eight isolates, the symptoms on the detached leaves and fruits inoculated with isolate DE2 were identical to those observed in the field. Verifying Koch's postulates confirmed that DE2 was the pathogenic bacterium that causes the disease. Based on a 16S rRNA phylogenetic tree, isolate DE2 belongs to the genus Erwinia. Biolog and API 20E results also indicated that isolate DE2 is an undescribed species of Erwinia. Isolate DE2 was negative for oxidase. Subsequently, the complete genome sequence of isolate DE2 was determined and compared to the complete genome sequences of 29 other Erwinia species based on digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) analyses. The ANI and dDDH values between strain DE2 and Erwinia species were both below the species thresholds (ANI < 95-96%, dDDH<70%), suggesting that isolate DE2 is a new species of Erwinia. We will temporarily name strain DE2 as Erwinia pyri sp. nov. There were 548 predicted virulence factors in the genome of strain DE2, comprising 534 on the chromosome and 5 in the plasmids. The whole genome sequence of strain DE2 has been submitted to the NCBI database (ASM3075845v1) with accession number GCA_030758455.1. The strain DE2 has been preserved at the China Center for Type Culture Collection (CCTCC) under the deposit number CCTCC AB 2024080. This study represents the initial report of a potentially new bacterial species in the genus Erwinia that causes a novel pear dieback disease. The findings provide a valuable strain resource for the study of the genus Erwinia and establish a robust theoretical foundation for the prevention and control of emerging pear dieback diseases.

From predator to protector: Myxococcus fulvus WCH05 emerges as a potent biocontrol agent for fire blight

Fire blight, caused by the Gram-negative bacterium Erwinia amylovora, poses a substantial threat to pome fruit production worldwide. Despite existing control strategies, a pressing need remains for sustainable and environmentally friendly fire blight management. Myxobacteria, renowned for their predatory behavior and potent enzymes, emerge as a groundbreaking biocontrol approach with significant potential. Here, we report the biocontrol potential of a novel Myxococcus fulvus WCH05, against E. amylovora. Using various in vitro and planta assays, we demonstrated the multifaceted biocontrol abilities of strain WCH05. In plate predation assays, strain WCH05 exhibited not only strong predation against E. amylovora but also broad-spectrum activities against other plant pathogenic bacteria. Pre-treatment with strain WCH05 significantly decreased pear blossom blight incidence in detached inflorescence assays, achieving a controlled efficacy of 76.02% that rivaled the antibiotic streptomycin (79.79%). In greenhouse trials, strain WCH05 effectively reduced the wilting rate and disease index in young pear seedlings, exhibiting both protective (73.68%) and curative (68.66%) control. Further investigation revealed that the biocontrol activity of strain WCH05 relies on both direct contact and extracellular enzyme secretion. While cell extracts lacked inhibitory activity, ammonium sulfate-precipitated secreted proteins displayed potent lytic activity against E. amylovora. Substrate spectrum analysis identified peptidases, lipases, and glycosidases among the secreted enzymes, suggesting their potential roles in pathogen degradation and biocontrol efficacy. This study presents the first evidence of Myxococcus fulvus WCH05 as a biocontrol agent against fire blight. Its potent predatory abilities and enzymatic arsenal highlight its potential for sustainable disease management in pome fruit production. Future research will focus on identifying and characterizing specific lytic enzymes and optimizing strain WCH05 application strategies for field efficacy.

Isolation and Characterization of a Lytic Bacteriophage RH-42-1 of Erwinia amylovora from Orchard Soil in China

Fire blight, caused by the bacterium Erwinia amylovora, is a major threat to pear production worldwide. Bacteriophages, viruses that infect bacteria, are a promising alternative to antibiotics for controlling fire blight. In this study, we isolated a novel bacteriophage, RH-42-1, from Xinjiang, China. We characterized its biological properties, including host range, plaque morphology, infection dynamics, stability, and sensitivity to various chemicals. RH-42-1 infected several E. amylovora strains but not all. It produced clear, uniform plaques and exhibited optimal infectivity at a multiplicity of infection (MOI) of 1, reaching a high titer of 9.6 × 109 plaque-forming units (PFU)/mL. The bacteriophage had a short latent period (10 min), a burst size of 207 PFU/cell, and followed a sigmoidal one-step growth curve. It was stable at temperatures up to 60 °C but declined rapidly at higher temperatures. RH-42-1 remained viable within a pH range of 5 to 9 and was sensitive to extreme pH values. The bacteriophage demonstrates sustained activity upon exposure to ultraviolet radiation for 60 min, albeit with a marginal reduction. In our assays, it exhibited a certain level of resistance to 5% chloroform (CHCl3), 5% isopropanol (C3H8O), and 3% hydrogen peroxide (H2O2), which had little effect on its activity, whereas it showed sensitivity to 75% ethanol (C2H5OH). Electron microscopy revealed that RH-42-1 has a tadpole-shaped morphology. Its genome size is 14,942 bp with a GC content of 48.19%. Based on these characteristics, RH-42-1 was identified as a member of the Tectiviridae family, Alphatectivirus genus. This is the first report of a bacteriophage in this genus with activity against E. amylovora.