ISHS Acta Horticulturae 338: VI International Workshop on Fireblight
LABORATORY AND FIELD ASSAYS FOR BIOLOGICAL CONTROL OF FIRE BLIGHT IN D'ANJOU PEAR |
| Authors: | R.J. McLaughlin, R.G. Roberts |
| Abstract:
Potential biological control agents were obtained from various sources and screened for ability to inhibit infection of immature pear (cv. d'Anjou) fruit slices by Erwinia amylovora. Strains were applied to fruit slices as 0.1 Abs600nm suspensions prepared test was enhanced if inoculation with E. amylovora (107 cfu/ml) was delayed by 6 hr. One unidentified strain and three strains of E. herbicola, two Arthrobacter spp., Pseudomonas viridiflava, and Pseudomonas fluorescens, were most effective in preventing infection of pear slices. Performance of these strains in blossom infection assays on forced shoots was inconsistent with results obtained in the pear slice assay. In addition, there were significant differences (P ≤ 0.05) in disease susceptibility of flower clusters in the control treatment, ie., those not treated with antagonists but inoculated with the pathogen, which made interpretation of results in this assay uncertain. In a 1991 field test, blossoms on whole tree replicates were sprayed to runoff twice (40% and 80% bloom) with E. herbicola strains C9–1 (source: Carol Ishimaru) and CN-1, and Pseudomonas fluorescens A506 (source: Steve Lindow), all at 108 cfu/ml, or with oxytetracycline at 150 ppm. Trees were inoculated with E. amylovora (107 cfu/ml) 48 hr (90–100% bloom) after treatment with antagonists. Trees treated with C9–1 or oxytetracyline had 40% less (P=0.05) blight (no. strikes per tree) than trees in the water control. A 1992 field test included more strains. Flowers on individual limbs were spray-inoculated with aquenous suspensions of the strains at 100% bloom and spray-inoculated 2 d later with E. amylovora. Results taken 18 d after pathogen inoculation showed that E. herbicola strains C9–1 and CN-1 and strain E-19 significantly reduced the percentage of blighted blossoms 41.6–48.5%, as compared to the control treatment that was pre-treated with water prior to pathogen inoculation. Oxytetracycline applied at 150 ppm did not significantly reduce blight in this trial. | |
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