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Project description

Improved biological control of fire blight of pear and apple by introduction of antagonistic bacteria into unopened flowers. (02BC005)
Program UC IPM competitive research grants program
Principal
investigator
S.E. Lindow, Plant and Microbial Biology, UC Berkeley
Host/habitat Pears; Apples; Tree Crops
Pest Fire Blight Erwinia amylovora
Discipline Plant Pathology
Beneficial
organism
Bacteria; Pseudomonas fluorescens
Review
panel
Biological Controls
Start year (duration)  2002 (Three Years)
Objectives Determine the magnitude of improved control of fire blight in pear and apple when antagonists are applied to unopened flowers with penetrating surfactants compared to repeated topical applications in water alone during the flowering period.

Measure the incidence of colonization by antagonistic bacteria applied to unopened flowers on cohorts of flowers that open at increasing times after inoculation.

Determine the localization of antagonistic bacteria in various flower parts after inoculation to unopened flowers with a penetrating surfactant.

Final report Application of Pseudomonas fluorescens strain A506 (in the form of the commercial bio-pesticide Blightban A506) with the organo-silicon surfactant Breakthru resulted in a higher proportion of colonized flowers on both Bartlett pear and Pink Lady apple, especially early in the growing season, than when the bacterium was applied in water alone. The proportion of flowers colonized with strain A506 throughout the spring generally increased with increasing concentrations of surfactant in which the bacteria were applied in a single application at the time of first bloom. Importantly, most flowers emerging from trees that were inoculated with strain A506 only a single time at "first bloom" with Blightban A506 in 0.2% or 0.5% Breakthru were as high as or higher throughout the main bloom, and into delayed bloom, than that on trees that received weekly applications of the same amount of Blightban A506. The most effective colonization of flowers from the single early-season spray application of antagonist with surfactant occurred in orchards in which most of the flowers, while not yet open, were poised to open; less colonization occurred in orchards that was sprayed at an earlier stage of bloom. No russeting of fruit was observed in any plot when surfactant was applied before substantial bloom had occurred. The number of applications of strain A506 apparently can be reduced by applying the antagonistic bacterium early in the season with a penetrating surfactant.

Third-year
progress
Application of Pseudomonas fluorescens strain A506 (in the form of the commercial bio-pesticide Blightban A506) with the organo-silicon surfactant Breakthrough resulted in a higher proportion of colonized flowers on both Bartlett pear and Pink Lady apple, especially early in the growing season, than when the bacterium was applied in water alone. The proportion of flowers colonized with strain A506 throughout the spring generally increased with increasing concentrations of surfactant in which the bacteria were applied in a single application at the time of first bloom. Importantly, most flowers emerging from trees that were inoculated with strain A506 only a single time at "first bloom" with Blightban A506 in 0.2% or 0.5% Breakthru were as high as or higher throughout the main bloom, and into delayed bloom, than that on trees that received weekly applications of the same amount of Blightban A506. The most effective colonization of flowers from the single early-season spray application of antagonist with surfactant occurred in the two orchards in which most of the flowers, while not yet open, were poised to open; much less colonization occurred in the orchard which was sprayed at an earlier stage of bloom. No russeting of fruit was observed in any plot when surfactant was applied before substantial bloom had occurred. Applying the antagonistic bacterium early in the season with a penetrating surfactant apparently can reduce the number of applications of strain A506.

Second-year
progress
Application of Pseudomonas fluorescens strain A506 (in the form of the commercial bio-pesticide Blightban A506) with the organo-silicon surfactant Breakthru resulted in a higher proportion of colonized flowers on both Bartlett pear and Pink Lady apple, especially early in the growing season, than when the bacterium was applied in water alone. The proportion of flowers colonized with strain A506 throughout the spring generally increased with increasing concentrations of surfactant in which the bacteria were applied in a single application at the time of first bloom. Importantly, most flowers emerging from trees that were inoculated with strain A506 only a single time at "first bloom" with Blightban A506 in 0.2% or 0.5% Breakthru were as high as or higher throughout the main bloom, and into delayed bloom, than that on trees that received weekly applications of the same amount of Blightban A506. The most effective colonization of flowers from the single early-season spray application of antagonist with surfactant occurred in the two orchards in which most of the flowers, while not yet open, were poised to open; much less colonization occurred in the orchard which was sprayed at an earlier stage of bloom. No russeting of fruit was observed in any plot when surfactant was applied before substantial bloom had occurred. The number of applications of strain A506 apparently can be reduced by applying the antagonistic bacterium early in the season with a penetrating surfactant.

First-year
progress
Application of Pseudomonas fluorescens strain A506 (in the form of the commercial bio-pesticide Blightban A506) with the organo-silicon surfactant Breakthru resulted in a higher proportion of colonized flowers on both Bartlett pear and Pink Lady apple, especially early in the growing season than when the bacterium was applied in water alone. The proportion of flowers colonized with strain A506 throughout the spring generally increased with increasing concentrations of surfactant in which the bacteria were applied in a single application at the time of first bloom. Importantly, most flowers emerging from trees that were inoculated with strain A506 only a single time at "first bloom" with Blightban A506 in 0.2% or 0.5% Breakthru were as high as or higher throughout the main bloom, and into delayed bloom than that on trees that received weekly applications of the same amount of Blightban A506. A highly significant linear correlation was observed between the logarithm of population sizes of strain A506 in individual flowers and the fraction of those flowers on which this strain was detected by a simple "flower rub" assay, suggesting that a simple qualitative assay for the presence of the antagonist in flowers can provide useful information both on the incidence of flower colonization and on population size. No russetting of fruit was observed in any plot when surfactant was applied before substantial bloom had occurred. Russetting of fruit was observed only in special test plots in which trees were treated with surfactant at mid-bloom or later. The number of applications of strain A506 apparently can be reduced by applying the antagonistic bacterium early in the season with a penetrating surfactant.

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