|Stockwell, V - OREGON STATE UNIVERSITY|
|Temple, T - OREGON STATE UNIVERSITY|
|Johnson, K - OREGON STATE UNIVERSITY|
Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2005
Publication Date: August 1, 2005
Citation: Stockwell, V.0., Temple, T., Johnson, K., Loper, J.E. 2005. Effect of the iron chelate feeddha on control of fire blight by Pseudomonas fluorescens A506. Phytopathology 95:S100. Technical Abstract: The biocontrol agent Pseudomonas fluorescens A506 produces an antibiotic toxic to Erwinia amylovora on media amended with iron. We tested the influence of the iron chelate FeEDDHA on growth of A506 on flowers and on fire blight suppression in orchard trials from 2000 to 2004. Pear and apple trees were treated with water, FeEDDHA (Sequestrene 138, 3 mM FeEDDHA), A506, or A506 plus FeEDDHA at 30 and 80% bloom. Agrimycin (streptomycin, 100 ppm a.i.) or Mycoshield (oxytetracycline, 200 ppm a.i.) applied at 80% and full bloom served as comparative standards. At full bloom, orchards were inoculated with E. amylovora. Population sizes of A506 on flowers were not affected by FeEDDHA. Among trials, A506 significantly decreased the incidence of fire blight by 24% compared to water-treated controls. Adding FeEDDHA to A506 significantly improved control compared to A506 alone and reduced the disease incidence by 56%. Agrimycin reduced the disease incidence by 71%. We also evaluated fire blight suppression with a gacS mutant of A506 that does not produce the antibiotic. The gacS mutant colonized flowers like A506, but had no effect on incidence of disease relative to water-treated controls. The results suggest that FeEDDHA induces A506 to produce an antibiotic on flowers, which improves suppression of fire blight by this strain.