Submitted to: Fire Blight International Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 2/15/2004
Publication Date: 7/5/2004
Citation: Stockwell, V.O., Temple, T.N., Johnson, K.B., Loper, J.E. 2004. Effect of the iron chelate FeEDDHA on control of fire blight by Pseudomonas fluorescens A506. 10th International Workshop on Fire Blight. Interpretive Summary: None required for an Abstract
Technical Abstract: The biocontrol agent Pseudomonas fluorescens A506 produces an antibiotic toxic to E. amylovora on media amended with iron. We hypothesized that increasing the iron content of the blossom habitat will increase the control of fire blight by A506. We tested the influence of the iron chelate FeEDDHA on growth of A506 on flowers and on fire blight suppression in 11 orchard trials in 2000 to 2003. Pear and apple trees were treated with water, FeEDDHA (Sequestrene 138, 1.2 g/L or 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 Ea153N, a streptomycin sensitive strain. Population size of A506 on flowers was not affected by FeEDDHA. Diseased blossom clusters on trees were cut and counted as symptoms developed post bloom. Overall, A506 decreased the incidence of disease by 28% compared to water-treated controls; this level of control was statistically similar to that provided by Mycoshield (38% reduction). FeEDDHA added to A506 significantly improved control compared to A506 alone, decreasing disease incidence by 53%. Agrimycin provided the best suppression of disease caused by the streptomycin-sensitive Ea153N (76%). We also evaluated fire blight suppression with a gacS mutant of A506 that does not produce the iron-associated 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 incrementally improves suppression of fire blight by this strain.