Articles
SECONDARY SPREAD BY ANTAGONISTIC BACTERIA AMONG PEAR AND APPLE BLOSSOMS
Article number
489_92
Pages
529 – 530
Language
Abstract
Fire blight of pear and apple, caused by Erwinia amylovora, is controlled biologically when epiphytic, antagonistic bacteria (Pantoea agglomerans or Pseudomonas fluorescens) become established on stigmas of blossoms prior to colonization by the pathogen.
Our objective has been to understand both environmental and biological factors affecting dispersal (spread) of antagonistic bacteria from colonized sites to previously unoccupied stigmas, and the effect of this spread on disease suppression.
These experiments have been conducted by spraying antagonist suspensions onto the center rows of orchard blocks at mid-bloom.
Immediately after spraying, antagonists were detected only on treated blossoms, but as bloom progressed, stigmas colonized by marked strains of P. agglomerans or P. fluorescens occurred up to 10 m from treated trees.
High proportions of honey bees sampled near treated trees were infested with the antagonist strains, suggesting that this insect is an important vector for dispersal of antagonists from blossom to blossom.
In cage experiments in which bees were used to inoculate trees with E. amylovora, blossoms colonized by P. agglomerans or P. fluorescens on non-inoculated trees have suppressed the population size of the pathogen on stigmas and reduced disease frequency.
Environments in pear and apple blocks that bloomed at different times were compared and related to the proportion of non-inoculated blossoms colonized by P. agglomerans. Temperature is apparently an important factor affecting the rate of secondary spread of this antagonist.
Use of streptomycin as an agent to clear potential indigenous competitors from stigmas (i.e., naturally occurring bacterial epiphytes) did not enhance the rate of secondary spread by a streptomycin-resistant strain of P. agglomerans.
Our objective has been to understand both environmental and biological factors affecting dispersal (spread) of antagonistic bacteria from colonized sites to previously unoccupied stigmas, and the effect of this spread on disease suppression.
These experiments have been conducted by spraying antagonist suspensions onto the center rows of orchard blocks at mid-bloom.
Immediately after spraying, antagonists were detected only on treated blossoms, but as bloom progressed, stigmas colonized by marked strains of P. agglomerans or P. fluorescens occurred up to 10 m from treated trees.
High proportions of honey bees sampled near treated trees were infested with the antagonist strains, suggesting that this insect is an important vector for dispersal of antagonists from blossom to blossom.
In cage experiments in which bees were used to inoculate trees with E. amylovora, blossoms colonized by P. agglomerans or P. fluorescens on non-inoculated trees have suppressed the population size of the pathogen on stigmas and reduced disease frequency.
Environments in pear and apple blocks that bloomed at different times were compared and related to the proportion of non-inoculated blossoms colonized by P. agglomerans. Temperature is apparently an important factor affecting the rate of secondary spread of this antagonist.
Use of streptomycin as an agent to clear potential indigenous competitors from stigmas (i.e., naturally occurring bacterial epiphytes) did not enhance the rate of secondary spread by a streptomycin-resistant strain of P. agglomerans.
Publication
Authors
K.B. Johnson, V.O. Stockwell
Keywords
biological control
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