scholarly journals Implications of Pathogenesis by Erwinia amylovora on Rosaceous Stigmas to Biological Control of Fire Blight

2009 ◽  
Vol 99 (2) ◽  
pp. 128-138 ◽  
Author(s):  
K. B. Johnson ◽  
T. L. Sawyer ◽  
V. O. Stockwell ◽  
T. N. Temple
Keyword(s):  
Biological Control ◽  
Population Size ◽  
Fire Blight ◽  
Erwinia Amylovora ◽  
Fluorescent Protein ◽  
Virulent Strain ◽  
Avirulent Strain ◽  
Bacterial Antagonists ◽  
Population Sizes ◽  
Green Fluorescent

As a prerequisite to infection of flowers, Erwinia amylovora grows epiphytically on stigmas, which provide a conducive habitat for bacterial growth. Stigmas also support growth of several other bacterial genera, which allows for biological control of fire blight; although, in practice, it is very difficult to exclude E. amylovora completely from this habitat. We investigated the dynamics of growth suppression of E. amylovora by comparing the ability of virulent and avirulent strains of E. amylovora to compete with each other on stigmas of pear, apple, and blackberry, and to compete with a co-inoculated mixture of effective bacterial antagonists. When strains were inoculated individually, virulent E. amylovora strain Ea153N attained the highest population size on stigmas, with population sizes that were approximately double those of an avirulent hrpL mutant of Ea153 or the bacterial antagonists. In competition experiments, growth of the avirulent derivative was suppressed by the antagonist mixture to a greater extent than the virulent strain. Unexpectedly, the virulent strain enhanced the population size of the antagonist mixture. Similarly, a small dose of virulent Ea153N added to inoculum of an avirulent hrpL mutant of Ea153 significantly increased the population size of the avirulent strain. A pathogenesis-gene reporter strain, Ea153 dspE::gfp, was applied to flowers and a subset of the population expressed the green fluorescent protein while growing epiphytically on stigmas of apple. These results are consistent with the hypothesis that virulent E. amylovora modifies the epiphytic habitat presented by the stigma through a pathogenesis-related process, which increases host resources available to itself and, coincidentally, to nonpathogenic competitors. Over nine orchard trials, avirulent Ea153 hrpL significantly suppressed the incidence of fire blight four times compared with six for the antagonist mixture. The degree of biological control achievable with an avirulent strain of E. amylovora likely is limited by its inability to utilize the stigmatic habitat to the same degree as a virulent strain.

scholarly journals Control of Fire Blight by Pseudomonas fluorescens A506 and Pantoea vagans C9-1 Applied as Single Strains and Mixed Inocula

2010 ◽  
Vol 100 (12) ◽  
pp. 1330-1339 ◽  
Author(s):  
V. O. Stockwell ◽  
K. B. Johnson ◽  
D. Sugar ◽  
J. E. Loper
Keyword(s):  
Biological Control ◽  
Pseudomonas Fluorescens ◽  
Fire Blight ◽  
Erwinia Amylovora ◽  
Field Trials ◽  
Disease Suppression ◽  
Biological Control Agents ◽  
Population Sizes ◽  
Mixed Inocula ◽  
Pantoea Vagans

The biological control agents Pseudomonas fluorescens A506 and Pantoea vagans C9-1 were evaluated individually and in combination for the suppression of fire blight of pear or apple in 10 field trials inoculated with the pathogen Erwinia amylovora. The formulation of pathogen inoculum applied to blossoms influenced establishment of the pathogen and the efficacy of biological control. Pantoea vagans C9-1 suppressed fire blight in all five trials in which the pathogen was applied as lyophilized cells but in none of the trials in which the pathogen was applied as freshly harvested cells. In contrast, Pseudomonas fluorescens A506 reduced disease significantly in only one trial. A mixture of the two strains also suppressed fire blight, but the magnitude of disease suppression over all field trials (averaging 32%) was less than that attained by C9-1 alone (42%). The two biological control agents did not antagonize one another on blossom surfaces, and application of the mixture of A506 and C9-1 to blossoms resulted in a greater proportion of flowers having detectable populations of at least one bacterial antagonist than the application of individual strains. Therefore, the mixture of A506 and C9-1 provided less disease control than expected based upon the epiphytic population sizes of the antagonists on blossom surfaces. We speculate that the biocontrol mixture was less effective than anticipated due to incompatibility between the mechanisms by which A506 and C9-1 suppress disease.

scholarly journals Establishment of Bacterial Antagonists of Erwinia amylovora on Pear and Apple Blossoms as Influenced by Inoculum Preparation

1998 ◽  
Vol 88 (6) ◽  
pp. 506-513 ◽  
Author(s):  
V. O. Stockwell ◽  
K. B. Johnson ◽  
J. E. Loper
Keyword(s):  
Fire Blight ◽  
Erwinia Amylovora ◽  
Culture Media ◽  
Field Trials ◽  
Bacterial Cells ◽  
Fluorescent Microspheres ◽  
Bacterial Antagonists ◽  
Spray Inoculation ◽  
Population Sizes ◽  
Inoculum Preparation

The influence of inoculum preparation on the establishment of bacterial antagonists that suppress fire blight and Erwinia amylovora on blossoms was evaluated. Aqueous suspensions of Pseudomonas fluorescens A506, E. herbicola C9-1R, or E. amylovora 153N were prepared from cells harvested from the surface of an agar medium or from cells that were lyophilized after culture under similar conditions. Bacterial suspensions (1 × 108 CFU/ml) were sprayed on pear and apple trees at 50% bloom near midday. The incidence of recovery (proportion of blossoms containing detectable populations) and the population sizes of the bacteria on individual blossoms with detectable populations were followed over a period of several days. Fluorescent microspheres (1 μm in diameter) were added to sprays at a concentration of 1 × 107 microspheres per ml to mark blossoms that were open during application of bacteria. After dilution-plating, the stigmas and styles of each blossom were examined for the presence of microspheres with an epifluorescence microscope. In three of five trials, bacteria applied as suspensions of lyophilized cells were recovered from a greater proportion of blossoms than bacterial cells harvested directly from culture media. Every blossom harvested within 6 days after spraying had microspheres present on the surfaces of the styles and stigmas; thus, lack of establishment of detectable populations, rather than escape of blossoms from spray inoculation, accounted for the differences in proportion of blossoms colonized by the different preparations of bacteria. The use of lyophilized cells in field trials decreased variability in the establishment of bacteria on blossoms.

scholarly journals Field Evaluation of Biological Control of Fire Blight in the Eastern United States

Plant Disease ◽  
2009 ◽  
Vol 93 (4) ◽  
pp. 386-394 ◽  
Author(s):  
George W. Sundin ◽  
Nicole A. Werner ◽  
Keith S. Yoder ◽  
Herb S. Aldwinckle
Keyword(s):  
United States ◽  
New York ◽  
Biological Control ◽  
Fire Blight ◽  
Field Evaluation ◽  
Pantoea Agglomerans ◽  
Eastern United States ◽  
Bacterial Antagonists ◽  
Bacterial Endospores ◽  
Control Options

The bacterial antagonists Pseudomonas fluorescens A506, Pantoea agglomerans C9-1, and Pantoea agglomerans E325 and preparations of Bacillus subtilis QST 713 containing bacterial endospores and lipopeptide metabolites were evaluated for efficacy in controlling fire blight in Michigan, New York, and Virginia. When examined individually, the biological control materials were not consistently effective in reducing blossom infection. The average reduction in blossom infection observed in experiments conducted between 2001 and 2007 was variable and ranged from 9.1 to 36.1%, while control with streptomycin was consistent and ranged from 59.0 to 67.3%. Incidence of blossom colonization by the bacterial antagonists was inconsistent, and <60% of stigmata had the antagonists present in 12 of 25 experiments. Consistent control of blossom infection was observed when the biological control materials were integrated into programs with streptomycin, resulting in a reduction of the number of streptomycin applications needed to yield similar levels of control. Our results indicate that the prospects for biological control of fire blight in the eastern United States are currently not high due to the variability in efficacy of existing biological control options.

New potential bacterial antagonists for the biocontrol of fire blight disease (Erwinia amylovora) in Morocco

2018 ◽  
Vol 117 ◽  
pp. 7-15 ◽  
Author(s):  
Smail Ait Bahadou ◽  
Abderrahmane Ouijja ◽  
Abdelkarim Karfach ◽  
Abdessalem Tahiri ◽  
Rachid Lahlali
Keyword(s):  
Fire Blight ◽  
Erwinia Amylovora ◽  
Bacterial Antagonists ◽  
Blight Disease

scholarly journals Colonization of Host Plants by the Fire Blight Pathogen Erwinia amylovora Marked with Genes for Bioluminescence and Fluorescence

1998 ◽  
Vol 88 (5) ◽  
pp. 416-421 ◽  
Author(s):  
Jochen Bogs ◽  
Iris Bruchmüller ◽  
Claudia Erbar ◽  
Klaus Geider
Keyword(s):  
Host Plants ◽  
Fire Blight ◽  
Erwinia Amylovora ◽  
Vibrio Fischeri ◽  
Bacterial Invasion ◽  
Leaf Hairs ◽  
Lux Operon ◽  
And Migration ◽  
Green Fluorescent ◽  
Lac Promoter

To follow the movement of Erwinia amylovora in plant tissue without dissection, this bacterium was marked with either the lux operon from Vibrio fischeri or the gfp gene from the jellyfish Aequorea victoria, both carried on multicopy plasmids and expressed under the control of the lac promoter from Escherichia coli. Movement of the pathogen was visualized in leaves, stems, and roots of apple seedlings, and migration of E. amylovora was traced from inoculation sites in the stem to as far as the roots. Green fluorescent E. amylovora cells were observed in the xylem and later appeared to break out of the vessels into the intercellular spaces of the adjacent parenchyma. Inoculation in the intercostal region of leaves caused a zone of slow necrosis that finally resulted in bacterial invasion of the xylem vessels. Labeled bacteria could also be seen in association with the anchor sites of leaf hairs. Distortion of the epidermis adjacent to leaf hairs created openings that were observed by scanning electron microscopy. As the intercostal region, the bases of leaf hairs provided E. amylovora access to intact xylem vessels, which allowed further distribution of the pathogen in the host plant.

scholarly journals Epiphytic Bacteria and Yeasts on Apple Blossoms and Their Potential as Antagonists of Erwinia amylovora

2009 ◽  
Vol 99 (5) ◽  
pp. 571-581 ◽  
Author(s):  
P. Lawrence Pusey ◽  
Virginia O. Stockwell ◽  
Mark Mazzola
Keyword(s):  
Relative Humidity ◽  
Fire Blight ◽  
Erwinia Amylovora ◽  
Acid Methyl Ester ◽  
Washington State ◽  
Microbial Populations ◽  
Acid Methyl ◽  
Population Sizes ◽  
Average Relative Humidity ◽  
Cryptococcus Spp

Apple blossoms were sampled for indigenous epiphytic populations of culturable microorganisms during different stages of bloom at two locations in central Washington State and one site in Corvallis, OR. Frequencies and population sizes of bacteria on stigmas of apple were lower in Washington than at Corvallis, where average relative humidity was higher and possibly favored greater colonization; however, bacteria at Corvallis were mainly pseudomonads, whereas those in Washington were diverse, composed of several genera. In Washington, yeast as well as bacteria were isolated from both stigmatic and hypanthial surfaces. Sampled blossoms were processed immediately to assess microbial populations, or after a 24-h incubation at 28°C and high relative humidity, which broadened the range of detectable taxa evaluated as potential antagonists. Identifications were based on fatty acid methyl ester profiles and rDNA sequence analyses. Yeasts or yeastlike organisms were detected at frequencies similar to or greater than bacteria, particularly in hypanthia. When microbial isolates were tested for their capacity to suppress Erwinia amylovora on stigmas of detached crab apple flowers, many were ineffective. The best antagonists were the bacteria Pantoea agglomerans and Pseudomonas spp. and a few yeasts identified as Cryptococcus spp. Further evaluation of these taxa on flowers could lead to the discovery of additional biocontrol agents for fire blight.

scholarly journals Pathogenesis of Yersinia pestis Infection in BALB/c Mice: Effects on Host Macrophages and Neutrophils

2005 ◽  
Vol 73 (11) ◽  
pp. 7142-7150 ◽  
Author(s):  
Roman A. Lukaszewski ◽  
Dermot J. Kenny ◽  
Rosa Taylor ◽  
D. G. Cerys Rees ◽  
M. Gill Hartley ◽  
...  
Keyword(s):  
Yersinia Pestis ◽  
Fluorescent Protein ◽  
Virulent Strain ◽  
Late Phase ◽  
Flow Cytometric Analysis ◽  
Annexin V ◽  
Intracellular Bacteria ◽  
Necrosis Factor Alpha ◽  
Green Fluorescent

ABSTRACT The pathogenesis of infection with Yersinia pestis, the causative agent of plague, was examined following subcutaneous infection of BALB/c mice with a fully virulent strain expressing green fluorescent protein. Plate culturing, flow cytometry, and laser confocal microscopy of spleen homogenates throughout infection revealed three discernible stages of infection. The early phase was characterized by the presence of a small number of intracellular bacteria mostly within CD11b+ macrophages and Ly-6G+ neutrophils. These bacteria were not viable, as determined by plate culturing of spleen homogenates, until day 2 postinfection. Between days 2 and 4 postinfection, a plateau phase was observed, with bacterial burdens of 103 to 104 CFU per spleen. Flow cytometric analysis revealed that there was even distribution of Y. pestis within both CD11b+ macrophage and Ly-6G+ neutrophil populations on day 2 postinfection. However, from day 3 postinfection onward, intracellular bacteria were observed exclusively within splenic CD11b+ macrophages. The late phase of infection, between days 4 and 5 postinfection, was characterized by a rapid increase in bacterial numbers, as well as escape of bacteria into the extracellular compartment. Annexin V staining of spleens indicated that a large proportion of splenic neutrophils underwent rapid apoptosis on days 1 and 2 postinfection. Fewer macrophages underwent apoptosis during the same period. Our data suggest that during the early stages of Y. pestis infection, splenic neutrophils are responsible for limiting the growth of Y. pestis and that splenic macrophages provide safe intracellular shelters within which Y. pestis is able to grow and escape during the later stages of infection. This macrophage compliance can be overcome in vitro by stimulation with a combination of gamma interferon and tumor necrosis factor alpha.

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