ISHS Acta Horticulturae 338: VI International Workshop on Fireblight
EPIPHYTIC BACTERIA REDUCE ESTABLISHMENT AND POPULATION SIZE OF HONEY-BEE DISPERSED ERWINIA AMYLOVORA IN PEAR BLOSSOMS |
| Authors: | K. B. Johnson, V. O. Stockwell, Randy J. McLaughlin, D. Sugar, Joyce E. Loper, R. Roberts |
| Abstract:
In the springs of 1991 and 1992, a bee hive was placed in blocks of 40 Bartlett pear trees enclosed with 30% shade cloth at Medford, Oregon and Wenatchee, Washington (1992 only). During bloom, bees inside the enclosure were infested with a freeze-dried, nalidixic acid resistant strain of E. amylovora (105 to 106 cfu/bee) as they exited their hive and began foraging activity. Two to 4 spray applications of water, streptomycin sulfate, nalidixic acid, or a combination of the bacterial antagonists, Pseudomonas fluorescens strain A506 and E. herbicola strain C9–1 (108 cfu/ml), were applied to trees within the enclosure during bloom. At Medford in 1991 and Wenatchee in 1992, frequency of recovery of bacterial antagonists in individually sampled blossoms from treated trees exceeded 95% at full bloom but averaged less than 60% in Medford in 1992. One week after full bloom, 43% (Medford 1991), 27% (Medford 1992), and 48% (Wenatchee 1992) of water-treated blossoms had detectable populations of nalidixic acid resistant E. amylovora. At this same bloom stage, trees treated with bacterial antagonists always had significantly lower (P < 0.05) frequency of E. amylovora nalR in blossoms: 18–20% in Medford in 1991, 9–15% in Medford in 1992, and 8–17% in Wenatchee in 1992. In 1991 at Medford, 4% of blossoms treated with bacterial antagonists developed populations of E. amylovora nalR that exceeded 105 cfu/blossom compared to 19% of those treated with water; however, this suppression of population size of E. amylovora by bacterial antagonists was less apparent in 1992. In 1991, incidence of blossom clusters diseased with Fire Blight averaged 8, 0.1, and 1% for the water, stroptomycin, and bacterial antagonists treatments, respectivily; in 1992, the proportion of diseased blossom clusters in these same treatments in Medford averaged 44, 2 and 22% respectivily, and 9, 2.5, and 4%, respectivily, in Wenatchee. | |
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