In-orchard population dynamics of Erwinia amylovora on apple flower stigmas

Populations of the fire blight pathogen Erwinia amylovora Ea110 on apple flower stigmas were tracked over the course of apple bloom in field studies conducted between 2016 and 2019. In 18 of 23 experiments, flower stigmas inoculated on the 1st day of opening were found to harbor large (106-107 cells / flower) populations of E. amylovora when assessed three to five days post-inoculation. However, populations inoculated on stigmas of flowers that were already open for three days did not reach 106 cells / flower, and populations inoculated on stigmas of flowers that were already open for five days never exceeded 104 cells / flower. During this study, >10-fold increases in E. amylovora stigma populations in a 24-hr time period (termed population surges) were observed on 34.8%, 20.0%, and 4.0% of possible days on 1-day, 3-day, and 5-day open flowers, respectively. Population surges occurred on days with average temperatures as high as 24.5°C and as low as 6.1°C. Experiments incorporating more frequent sampling during days and overnight revealed that many population surges occurred between 10:00 PM and 2:00 AM. A Pearson’s correlation analysis of weather parameters occurring during surge events indicated that population surges were significantly associated with situations where overnight temperatures either increased or remained constant, where wind speed decreased, and where relative humidity increased. This study refines our knowledge of E. amylovora population dynamics and further indicates that E. amylovora is able to infect flowers during exposure to colder field temperatures than previously reported.

Draft Genome Sequences of Four Streptomycin-Sensitive Erwinia amylovora Strains Isolated from Commercial Apple Orchards in Ohio

Erwinia amylovora is the causative agent of fire blight, a devastating disease of apples and pears worldwide. Here, we report draft genome sequences of four streptomycin-sensitive strains of E. amylovora that were isolated from diseased apple trees in Ohio.

Antibacterial Effect of Biosynthesized Zinc Oxide Nanoparticles against Erwinia amylovora and Induction of Crop Growth

Objectives: Zinc oxide nanoparticles (ZnO-NPs) are widely recognized as one of the most promising types of materials in a wide range of applications, including agriculture. Modern systemic efforts have identified several therapeutically active microalgae-derived compounds, including phenols, flavonoids and others. The antibacterial properties of the phenolic substances were demonstrated. Hence, the present study aims to exhibit the antibacterial activity of the bioactive compound capped silver nanoparticles under in vitro conditions. Methods: Bioactive compound separated by Solid-phase Extraction method. Dispersible Zinc oxide nanoparticles synthesized using the bioactive compound as the major capping agent. Zinc nitrate was used as starting material and its reduction was carried by phenolic components of Spirulina platensis aqueous extract from Zn2+ to ZnO. The synthesized Zinc oxide nanoparticles are characterized by H1 NMR spectroscopy. Conjugated nanoparticles are characterized physically by Scanning Electron Microscopy (SEM) analysis. SEM demonstrated particle sizes in the range 10–15 nm. ZnO nanoparticles demonstrated antibacterial activity against an isolated plant pathogen Erwinia amylovora. Time kill determination assay was done. Findings: Phenols obtained after Solid Phase Extraction. Hence, this was regarded as the maximum quantified bioactive compound of Spirulina platensis. H1 NMR spectroscopy analyses showed the presence of phenolic compounds and alcohols groups of long chain were also detected. In SEM analysis, the mean diameter of spherical Phenols-ZnOPs is less than 15 nm surrounded by the capping agent. In given time periods of 4, 8, 16, and 24 hour cells, concentrations of 1000µg/mL were 42 %, 33 %, 20 %, and 18 %. At 500 µg/mL of extract concentration, Spirulina platensis inhibited 50% bacterial proliferation (IC50) of Erwinia amylovora. A significant inhibitory effect (p<0.0001) was seen against the plant pathogenic strain. Novelty: In addition to their antibacterial activities, biosynthesized ZnO-NPs are thought to show promise efficacy as growth accelerators. The most dangerous bacterial disease of pear and apple trees is fire blight, caused by Erwinia amylovora. Phenolic capped ZnO-NPs have been found to be efficient plant pathogen antagonists.

Expression of the Type III Secretion System Genes in Epiphytic Erwinia amylovora Cells on Apple Stigmas Benefits Endophytic Infection at the Hypanthium

Erwinia amylovora causes fire blight on rosaceous plants. One of the major entry points of E. amylovora into hosts is flowers, where E. amylovora proliferates epiphytically on stigmatic and hypanthium surfaces and, subsequently, causes endophytic infection at the hypanthium. The type III secretion system (T3SS) is an important virulence factor in E. amylovora. Although the role of T3SS during endophytic infection is well characterized, its expression during epiphytic colonization and role in the subsequent infection is less understood. Here, we investigated T3SS gene expression in epiphytic E. amylovora on stigma and hypanthium of apple flowers under different relative humidities (RH). On stigma surfaces, T3SS was expressed in a high percentage of E. amylovora cells, and its expression promoted epiphytic growth. On hypanthium surfaces, however, T3SS was expressed in fewer E. amylovora cells than on the stigma, and displayed no correlation with epiphytic growth, even though T3SS expression is essential for infection. E. amylovora cells grown on stigmatic surfaces and then flushed down to the hypanthium displayed a higher level of T3SS expression than cells grown on the hypanthium surface alone. Furthermore, E. amylovora cells precultured on stigma had a higher potential to infect flowers than E. amylovora cells precultured in a T3SS-repressive medium. This suggests that T3SS induction during the stigmatic epiphytic colonization may be beneficial for subsequent infection. Finally, epiphytic expression of T3SS was influenced by RH. Higher percentage of stigmatic E. amylovora cells expressed T3SS under high RH than under low RH. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .