EVALUATION OF BIOLOGICAL CONTROL AGENTS, SYSTEMIC ACQUIRED RESISTANCE INDUCERS AND BACTERICIDES FOR THE CONTROL OF FIRE BLIGHT ON APPLE BLOSSOM

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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Activation of defense mechanism in Lehsua (Cordia myxa) through systemic acquired resistance inducers against Alternaria leaf spot disease

Journal of Plant Biochemistry and Biotechnology ◽

10.1007/s13562-020-00579-4 ◽

2020 ◽

Author(s):

Sushila Choudhary ◽

R. P. Ghasolia

Keyword(s):

Leaf Spot ◽

Systemic Acquired Resistance ◽

Defense Mechanism ◽

Acquired Resistance ◽

Leaf Spot Disease ◽

Spot Disease ◽

Alternaria Leaf Spot ◽

Cordia Myxa ◽

Resistance Inducers

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Comparison of Methods of Acibenzolar-S-Methyl Application for Post-Infection Fire Blight Suppression in Pear and Apple

Plant Disease ◽

10.1094/pdis-09-15-1062-re ◽

2016 ◽

Vol 100 (6) ◽

pp. 1125-1131 ◽

Cited By ~ 3

Author(s):

Kenneth B. Johnson ◽

Todd N. Temple

Keyword(s):

Fire Blight ◽

Systemic Acquired Resistance ◽

Acquired Resistance ◽

Foliar Spray ◽

Field Research ◽

Apple Rootstocks ◽

Pr Genes ◽

Treatment Timing ◽

Guide Field ◽

Pathogenesis Related

Greenhouse-grown, 1-year-old potted ‘Bosc’ pear and apple rootstock cultivars ‘M.9’ and ‘M.26’ were inoculated with the fire blight pathogen, Erwinia amylovora, and subjected to trunk paint, root drench, or foliar spray treatments with acibenzolar-S-methyl (ASM, 4 to 30 mg a.i./tree) to induce systemic acquired resistance. Each method of ASM treatment suppressed fire blight canker expansion by 22 to 25%. Furthermore, ASM application method and ASM treatment timing (at or ±3 weeks relative to inoculation) interacted significantly (P ≤ 0.02) in each experiment. A root drench was most effective when applied 3 weeks before inoculation (36% suppression) whereas trunk paints and foliar sprays were more effective at inoculation (43 and 34%, suppression, respectively). Sizes of fire blight cankers in potted apple rootstocks M.9 and M.26 (under scions ‘Gala’ or ‘Cameo’) inoculated directly with the pathogen were reduced by 82 and 87% after two pretreatments of ASM applied as a trunk paint or root drench, respectively. Expression of pathogenesis-related (PR) genes PR-1 and -2 in apple leaves sampled after an ASM trunk paint were elevated significantly (P ≤ 0.05) relative to control trees for at least 9 weeks after treatment. Results of this study are being used to guide field research on postinfection therapy with ASM in 1- to 10-year-old pear and apple trees where fire blight has proven difficult to manage with therapeutic pruning only.

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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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Strategies to Improve Biological Control of Soilborne Plant Diseases

Science Letters ◽

10.47262/sl/9.1.132021001 ◽

2021 ◽

Vol 9 (1) ◽

pp. 1-3

Keyword(s):

Biological Control ◽

Systemic Acquired Resistance ◽

Cultural Practices ◽

Acquired Resistance ◽

Complete Removal ◽

Plant Diseases ◽

Attractive Alternative ◽

Control Methods ◽

Complete Control ◽

Soilborne Diseases

Biological control of plant soilborne diseases has appeared as an attractive alternative to other control methods. For the biological control of plant soilborne diseases, microorganisms mainly bacteria and fungi are used, which suppress growth and virulence traits or even kill pathogens and induce plant systemic acquired resistance. In recent years, the demand for organic food increased the use of biological control agents; however, complete control of plant diseases has not been achieved yet. The beneficial microbes used for biological control of plant diseases perform admirably under controlled greenhouse conditions but are not always successful under field conditions, which highly discourages the biological control methods. Hence, complete removal of chemicals from agricultural systems may not be impossible but a logical reduction in their application is feasible. Therefore, systematic integrated methods including both chemical and biological control and other control methods like cultural practices, resistant varieties and crop rotation are highly recommended.

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BIOLOGICAL CONTROL AGENTS OF FIRE BLIGHT: SUCCESSES AND CHALLENGES

Acta Horticulturae ◽

10.17660/actahortic.2011.896.58 ◽

2011 ◽

pp. 409-416 ◽

Cited By ~ 4

Author(s):

J.L. Vanneste

Keyword(s):

Biological Control ◽

Fire Blight ◽

Biological Control Agents ◽

Successes And Challenges

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A Single Effector Protein, AvrRpt2EA, from Erwinia amylovora Can Cause Fire Blight Disease Symptoms and Induces a Salicylic Acid–Dependent Defense Response

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-12-17-0300-r ◽

2018 ◽

Vol 31 (11) ◽

pp. 1179-1191 ◽

Cited By ~ 10

Author(s):

Susan Schröpfer ◽

Christoph Böttcher ◽

Thomas Wöhner ◽

Klaus Richter ◽

John Norelli ◽

...

Keyword(s):

Salicylic Acid ◽

Fire Blight ◽

Systemic Acquired Resistance ◽

Erwinia Amylovora ◽

Acquired Resistance ◽

Inducible Promoter ◽

Marker Genes ◽

Effector Protein ◽

In Planta ◽

Natural Fire

The AvrRpt2EA effector protein of Erwinia amylovora is important for pathogen recognition in the fire blight–resistant crabapple Malus × robusta 5; however, little is known about its role in susceptible apples. To study its function in planta, we expressed a plant-optimized version of AvrRpt2EA driven by a heat shock–inducible promoter in transgenic plants of the fire blight–susceptible cultivar Pinova. After induced expression of AvrRpt2EA, transgenic lines showed shoot necrosis and browning of older leaves, with symptoms similar to natural fire blight infections. Transgenic expression of this effector protein resulted in an increase in the expression of the salicylic acid (SA)-responsive PR-1 gene but, also, in the levels of SA and its derivatives, with diverse kinetics in leaves of different ages. In contrast, no increase of expression levels of VSP2 paralogs, used as marker genes for the activation of the jasmonic acid (JA)-dependent defense pathway, could be detected, which is in agreement with metabolic profiling of JA and its derivatives. Our work demonstrates that AvrRpt2EA acts as a virulence factor and induces the formation of SA and SA-dependent systemic acquired resistance.

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Influence of Age of Apple Flowers on Growth of Erwinia amylovora and Biological Control Agents

Plant Disease ◽

10.1094/pdis.2003.87.5.502 ◽

2003 ◽

Vol 87 (5) ◽

pp. 502-509 ◽

Cited By ~ 25

Author(s):

S. V. Thomson ◽

S. C. Gouk

Keyword(s):

Biological Control ◽

Fire Blight ◽

Erwinia Amylovora ◽

Antagonistic Bacteria ◽

Biological Control Agents ◽

Limited Growth ◽

Bacterial Populations ◽

Arid Conditions ◽

Flower Age ◽

Causal Pathogen

The influence of flower age on growth of Erwinia amylovora, the causal pathogen of fire blight of apples and pears, was investigated under humid and arid conditions in Hamilton, New Zealand (NZ), and Logan, UT, USA, respectively. ‘Royal Gala’ apple flowers ranging from 1 to 8 days old were atomized with E. amylovora. Pistils were dissected and washed separately from the remaining floral parts (flowers ex pistils) for estimation of bacterial numbers. Pistils, 1 to 3 days old (USA) and 1 to 4 days old (NZ), supported exponential growth of E. amylovora, but bacterial populations did not increase when older flowers were inoculated. Scanning electron microscopy showed round and turgid papillae on stigmas of 1-day-old flowers. Papillae on 4- to 6-day-old stigmas were completely collapsed and covered in mucilage. Populations of E. amy-lovora on the flowers ex pistils were characteristically lower than pistil populations. High populations of saprophytic bacteria were found on both floral parts of all ages, but there was no difference in their numbers on 3- to 6-day-old pistils. This suggests their presence did not inhibit the growth of E. amylovora on older stigmas. The results demonstrate that stigmas on 1- to 3-day-old flowers often support rapid growth of E. amylovora, but flowers inoculated when more than 4 to 5 days old do not support growth or only limited growth. The same location and pattern of bacterial growth occurred with the biological control agents Pseudomonas fluorescens PfA506n and Pantoea agglomerans (Erwinia herbicola) Eh318nr. The distinct effect of flower age on growth of antagonistic bacteria and E. amylovora may be important in deciding when to treat with biological control organisms or bactericides.

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