Effect of antagonistic bacteria on establishment of honey bee-dispersed Erwinia amylovora in pear blossoms and on fire blight control
1993
Johnson, K.B. | Stockwell, V.O. | McLaughlin, R.J. | Sugar, D. | Loper, J.E. | Roberts, R.G.
In field trials conducted in 1991 and 1992 at Medford, OR, and in 1992 at Wenatchee, WA, Pseudomonas fluorescens strain A506 and Erwinia herbicola strain C9-1 established epiphytic populations on pear blossoms and were effective antagonists for the biological control of fire blight. Both bacterial antagonists, water, or streptomycin sulfate were applied to trees at 30% and full bloom. Pear trees were challenged inoculated with freeze-dried cells of E. amylovora vectored to blossoms by honey bees. One week after full bloom, the antagonists were established in more than 95% of treated blossoms in Oregon in 1991 and Washington in 1992, but in less than 50% of blossoms in Oregon in 1992. At the same bloom stage, 41% (Oregon, 1991), 27% (Oregon, 1992), and 49% (Washington, 1992) of water-treated blossoms had detectable populations of E. amylovora, whereas trees treated with bacterial antagonists always had a significantly lower (p < 0.05) percentage of blossoms with detectable E. amylovora populations: 18-20% (Oregon, 1991), 9-15% (Oregon, 1992), and 8-17% (Washington, 1992). In Oregon in 1991, only 4% of blossoms treated with bacterial antagonists supported populations of E. amylovora that exceeded 10(5) cfu per blossom compared with 19% of blossoms treated with water; however, suppression of population size of E. amylovora by bacterial antagonists was not apparent in 1992. In 1991, fire blight symptoms developed in 8, 0.1, and 1% of blossom clusters treated with water, streptomycin, or bacterial antagonists, respectively. In 1992, the percentage of diseased blossom clusters in these same treatments in Oregon averaged 44, 2, and 22%, respectively, and 9, 2.5, and 4%, respectively, in Washington.
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