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Project description

Enhancing Biological Control of Diseases and Frost Damage by Combining Antagonistic Bacteria with Penetrating Surfactants. (97BC009)
Program UC IPM competitive research grants program
S.E. Lindow, Plant and Microbial Biology, UC Berkeley
Host/habitat Apples; Pears; Tree Crops
Pest Unspecified Pathogens and Diseases
Discipline Plant Pathology
Antagonistic bacteria
Biological Controls
Start year (duration)  1997 (Three Years)
Objectives Determine the extent to which surfactants can enhance the population size of A506 (an antagonistic bacterium that is a registered biological control agent) on pear and apple.

Determine if the biological control of fire blight disease and frost injury to pear and apple is greater in the presence of a surfactant with very low surface tension than when the antagonist is applied in water alone.

Since the biological control of fire blight disease caused by the bacterium Erwinia amylovora, by biological control agents such as Pseudomonas fluorescens strain A506 is maximized when the biological control agent has completely colonized the target plant tissue before the arrival of the pathogen, we investigated whether silicon-based surfactants having low surface tension could facilitate colonization and hence biological control. Populations of strain A506 were from 3 to 100-fold higher on pear and apple flowers treated during bloom with a mixture of strain A506 and Breakthru (0.05%) than on flowers treated only with strain A506 in three field trials. The population size of strain A506 in pear flowers throughout the spring increased greatly with increasing concentrations of surfactant in which the bacteria were applied in a single application before bloom as well as with the age of the pear tissues at which the single inoculation was made. Importantly, the population size of strain A506 on flowers in the spring increased to over 10 cells/spur and 10 cells/spur on trees that were inoculated only a single time at "first bloom" with Blightban A506 in 0.1% or 0.5% Breakthru respectively. The population sizes of strain A506 on flowers in trees receiving a single application of Blightban A506 in a high rate of surfactant before bloom was much higher throughout the spring than on trees which received weekly application of the same amount of Blightban A506 without surfactant. Breakthru did not increase the severity of fruit russet to apple or pear when applied by itself or with strain A506 compared to control trees and russet severity was generally lower on trees treated with a mixture of strain A506 and Breakthru than on control trees. Fire blight disease control on apple was about 3 fold greater on trees treated with both strain A506 and Breakthru than with strain A506.

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