LABORATORY AND FIELD TRIALS WITH SELECTED MICROORGANISMS AS BIOCONTROL AGENTS FOR FIRE BLIGHT

Mixtures of biological control agents can be superior to individual agents in suppressing plant disease, providing enhanced efficacy and reliability from field to field relative to single biocontrol strains. Nonetheless, the efficacy of combinations of Pseudomonas fluorescens A506, a commercial biological control agent for fire blight of pear, and Pantoea vagans strain C9-1 or Pantoea agglomerans strain Eh252 rarely exceeds that of individual strains. A506 suppresses growth of the pathogen on floral colonization and infection sites through preemptive exclusion. C9-1 and Eh252 produce peptide antibiotics that contribute to disease control. In culture, A506 produces an extracellular protease that degrades the peptide antibiotics of C9-1 and Eh252. We hypothesized that strain A506 diminishes the biological control activity of C9-1 and Eh252, thereby reducing the efficacy of biocontrol mixtures. This hypothesis was tested in five replicated field trials comparing biological control of fire blight using strain A506 and A506 aprX::Tn5, an extracellular protease-deficient mutant, as individuals and combined with C9-1 or Eh252. On average, mixtures containing A506 aprX::Tn5 were superior to those containing the wild-type strain, confirming that the extracellular protease of A506 diminished the biological control activity of C9-1 and Eh252 in situ. Mixtures of A506 aprX::Tn5 and C9-1 or Eh252 were superior to oxytetracycline or single biocontrol strains in suppressing fire blight of pear. These experiments demonstrate that certain biological control agents are mechanistically incompatible, in that one strain interferes with the mechanism by which a second strain suppresses plant disease. Mixtures composed of mechanistically compatible strains of biological control agents can suppress disease more effectively than individual biological control agents.

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Strain-specific detection of two Aureobasidium pullulans strains, fungal biocontrol agents of fire blight by new, developed multiplex-PCR

Journal of Applied Microbiology ◽

10.1111/j.1365-2672.2007.03668.x ◽

2008 ◽

Vol 104 (5) ◽

pp. 1433-1441 ◽

Cited By ~ 18

Author(s):

I. Loncaric ◽

C. Donat ◽

B. Antlinger ◽

J.T. Oberlerchner ◽

B. Heissenberger ◽

...

Keyword(s):

Multiplex Pcr ◽

Aureobasidium Pullulans ◽

Fire Blight ◽

Biocontrol Agents ◽

Specific Detection

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Crab Apple Blossoms as a Model for Research on Biological Control of Fire Blight

Phytopathology ◽

10.1094/phyto.1997.87.11.1096 ◽

1997 ◽

Vol 87 (11) ◽

pp. 1096-1102 ◽

Cited By ~ 59

Author(s):

P. L. Pusey

Keyword(s):

Fire Blight ◽

Biocontrol Agents ◽

Suitable Model ◽

Bacterial Strains ◽

Bacterial Populations ◽

Cold Room ◽

Series Of Experiments ◽

Population Interactions ◽

Intact Crab ◽

Crab Apple

Nonseasonal availability of pomaceous flowers could improve laboratory detection and prefield testing of biocontrol agents for fire blight of pear and apple. Crab apple was selected as a model because of its high flower productivity on 1-year-old wood, high susceptibility to fire blight, and availability from nurseries. Cultivars Manchurian and Snowdrift were manipulated to bloom once by transferring dormant nursery trees from a cold room to a greenhouse and a second time by defoliating trees and applying 1% cytokinin and 0.1% gibberellins to the buds with a brush. Different sets of trees were induced at different times to bloom, so that flowers were produced 12 months in the year. When known bacterial antagonists (Erwinia herbicola strain C9-1 and Pseudomonas fluorescens strain A506) were applied alone or in combination to the stigmas of detached crab apple blossoms prior to inoculation with the pathogen (E. amylovora strain Ea153), population interactions over time were comparable to those reported in previous studies involving pear or apple. In a subsequent series of experiments, the relative effects of 12 bacterial strains on stigmatic populations of strain Ea153 were similar for detached blossoms of crab apple in the laboratory, blossoms of intact crab apple trees in the greenhouse, and blossoms of pear and apple in the field. Additionally, when stigmas of detached crab apple blossoms were inoculated with antagonists (strains C9-1 and A506) and the pathogen, and later subjected to a 24-h wetting period, bacterial populations in the flower hypanthium increased and disease was suppressed. These studies indicate that crab apple blossoms can serve as a suitable model for year-round evaluation and study of biocontrol agents for fire blight.

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

Phytopathology ◽

10.1094/phyto-03-10-0097 ◽

2010 ◽

Vol 100 (12) ◽

pp. 1330-1339 ◽

Cited By ~ 50

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.

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

Phytopathology ◽

10.1094/phyto.1998.88.6.506 ◽

1998 ◽

Vol 88 (6) ◽

pp. 506-513 ◽

Cited By ~ 52

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.

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Bee Vectoring: Development of the Japanese Orchard Bee as a Targeted Delivery System of Biological Control Agents for Fire Blight Management

Pathogens ◽

10.3390/pathogens9010041 ◽

2020 ◽

Vol 9 (1) ◽

pp. 41 ◽

Cited By ~ 1

Author(s):

Neelendra K. Joshi ◽

Henry K. Ngugi ◽

David J. Biddinger

Keyword(s):

Biological Control ◽

Targeted Delivery ◽

Fire Blight ◽

Erwinia Amylovora ◽

The United States ◽

Biocontrol Agents ◽

Efficient System ◽

Control Product ◽

Tree Fruits ◽

Potential Use

Fire blight, which is caused by the bacteria Erwinia amylovora, remains one of the most important diseases limiting the productivity of apple and pear orchards in the United States. In commercial orchards, in-season fire blight management relies exclusively on the use of antibiotic treatments (such as streptomycin and oxytetracycline) and on bacterial biocontrol agents whose efficacy is limited. We hypothesize that the efficacy of the biocontrol agents can be greatly enhanced through targeted delivery to flowers, which serve as initial infection courts, using the Japanese orchard bee, Osmia cornifrons. Many factors, such as the synchrony of life cycle with plant phenology and specificity to pomaceous plants, suggest that O. cornifrons could be an excellent vector of the biocontrol products during bloom in pome tree fruits. However, deployment of this pollinator species to deliver biocontrol agents for fire blight control has not been attempted previously due to the lack of an efficient system to pack the bodies of the bees exiting nesting tubes with the biocontrol products. In this study, we design and test a dispenser system to facilitate the use of O. conifrons as a vector for commercially available biocontrol products for fire blight control. The effectiveness of O. conifrons to deliver biocontrol agents to flowers, and to effect secondary dissemination from treated to untreated flowers is also evaluated in greenhouse experiments. We found that the O. conifrons bees were able to use the nest dispenser designed for the delivery of biological control products, and are effective in vectoring and delivering the Bacillus subtilis-based biological control product (Serenade®) to apple blossoms. We also found that the O. cornifrons were effective in secondary inoculation of this biological control product to newly-opened flowers. These findings suggest the potential use of commercially available O. conifrons and other orchard bees in targeted delivery of biological control products for fire blight, and possibly other diseases, in different fruit crops.

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CHARACTERISATION OF TWO FLUORESCENT STRAINS OF PSEUDOMONAS AS BIOCONTROL AGENTS AGAINST FIRE BLIGHT

Acta Horticulturae ◽

10.17660/actahortic.2002.590.44 ◽

2002 ◽

pp. 299-307 ◽

Cited By ~ 2

Author(s):

O. Galasso ◽

G. Sponza ◽

C. Bazzi ◽

J.L. Vanneste

Keyword(s):

Fire Blight ◽

Biocontrol Agents

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Asian Pear: A Potential Alternative Fruit Crop for Growers in the Mid-Atlantic Region

HortScience ◽

10.21273/hortsci10526-16 ◽

2016 ◽

Vol 51 (11) ◽

pp. 1325-1328

Author(s):

Christopher S. Walsh ◽

Julia M. Harshman ◽

Anna E. Wallis ◽

Amy Barton Williams ◽

Michael J. Newell ◽

...

Keyword(s):

Fire Blight ◽

Field Trials ◽

Pyrus Pyrifolia ◽

Eastern United States ◽

Good Opportunity ◽

European Pear ◽

Asian Pear ◽

Pear Trees ◽

Research And Education

Production of european pears (Pyrus communis L.) in the eastern United States is limited by a number of physiological and pathological problems. In an attempt to expand sustainable pear production in that region, a series of long-term field trials of asian pear [Pyrus pyrifolia (Burm. F) Nak. (syn. Pyrus serotina L.)] were established at two sites in Maryland. To compare precocity, productivity, and survival, nine asian pear cultivars and three European cultivars were planted in a replicated trial in 2010 at the Wye Research and Education Center (Wye REC). The asian pears were precocious and productive and many trees flowered and fruited in the second leaf. After the fourth leaf, survival of ‘Isi’iwasi’, ‘Shinsui’, ‘Kosui’, and ‘Olympic’ was good, while many ‘Hosui’ and ‘Ya Li’ (asian pear) trees as well as ‘Bartlett’ and ‘Golden Russett’ (european pear) trees had died at that point, following bloom infections of fire blight (Erwinia amylovora). At Keedysville (WMREC), 18 asian pear cultivars in two established plantings were evaluated for their field tolerance to fire blight following a severe hailstorm. The cultivars Shin Li, Daisu Li, Shinsui, and Olympic fared as well as Magness, a fire blight–tolerant european pear cultivar that served as a benchmark in that evaluation. Conversely, ‘Hosui’, ‘Choju’, ‘Kosui’, ‘Seigyoku’, ‘Ya Li’, and ‘Ts’e Li’ were severely damaged. Three consumer tastings were conducted using fruit from the Wye REC trial. ‘Yoinashi’, ‘Atago’, ‘Shinko’, and ‘Olympic’ were well received by consumers. After tasting asian pears, most people, even those less familiar with the crop, reported they would consider purchasing the fruit and requested the names of local producers. Based on our long-term research results, there appears to be a good opportunity for locally produced asian pear fruit. With the correct cultivar selection for fire blight management, local growers should be able to produce this alternative crop sustainably and market their fruit profitably.

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ESTABLISHMENT ON PEAR BLOSSOMS OF BIOCONTROL AGENTS FOR FIRE BLIGHT

Acta Horticulturae ◽

10.17660/actahortic.1993.338.58 ◽

1993 ◽

pp. 361-362

Author(s):

V.O. Stockwell ◽

J.E. Loper ◽

K.B. Johnson

Keyword(s):

Fire Blight ◽

Biocontrol Agents

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Field Evaluation of 64 Apple Rootstocks for Orchard Performance and Fire Blight Resistance

HortScience ◽

10.21273/hortsci.42.7.1517 ◽

2007 ◽

Vol 42 (7) ◽

pp. 1517-1525 ◽

Cited By ~ 33

Author(s):

Nicole L. Russo ◽

Terence L. Robinson ◽

Gennaro Fazio ◽

Herb S. Aldwinckle

Keyword(s):

Disease Resistance ◽

Root Rot ◽

Financial Risk ◽

Fire Blight ◽

Field Evaluation ◽

Field Trials ◽

Blight Resistance ◽

Apple Rootstocks ◽

Yield Efficiency ◽

Better Than

In 2002, apple rootstock trials using three scion cultivars were established at Geneva, NY, to evaluate 64 apple (Malus ×domestica Borkh.) rootstocks for horticultural performance and fire blight resistance. Field trials compared several elite Geneva® apple rootstocks, which were bred for tolerance to fire blight and Phytophthora root rot, to both commercial standards and elite rootstock clones from around the world. Three rootstocks performed well with all scion cultivars: ‘B.9’, ‘Geneva® 935’, and ‘Geneva® 41’. All three rootstocks were similar in size to ‘M.9’ clones but with elevated yield efficiency and superior resistance to fire blight. ‘Geneva® 11’ also performed very well with ‘Golden Delicious’ and ‘Honeycrisp’ with regard to yield efficiency and disease resistance. Resistant rootstocks greatly enhanced the survival of young trees, particularly with the susceptible scion cultivars ‘Gala’ and ‘Honeycrisp’. Results demonstrate the ability of new rootstock clones to perform better than current commercial standards, reducing financial risk to producers while promoting orchard health with enhanced disease resistance.

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