|Stockwell, Virginia -|
Submitted to: Acta Horticulturae
Publication Type: Abstract Only
Publication Acceptance Date: January 31, 2011
Publication Date: May 1, 2011
Citation: Pusey, P.L., Stockwell, V. 2011. Evidence that antibiotic of Pantoea agglomerans E325 is produced and active against Erwinia amylovora on stigmas of pomaceous blossoms. Acta Horticulturae. 896:463-465. Technical Abstract: Pantoea agglomerans strain E325, the active ingredient in a commercial product for fire blight, previously was shown to produce a unique pH-sensitive inhibitor in vitro that is specific to E. amylovora. To evaluate antibiosis as a mode of antagonism of E325, Tn5 mutagenesis was used to generate antibiotic-deficient mutants. One antibiotic-deficient mutant of E325 (E325ad1) had a rough colony morphology on King’s medium B, which differed from the hypermucoid colony morphology of the wildtype strain on that medium. The colony morphology of a second antibiotic-deficient mutant (E325ad2) was indistinguishable from the parent strain. In 2009, E325 and E325ad1 were tested as antagonists against E. amylovora (Ea153N) on stigmas of detached crab apple flowers and apple blossoms in the orchard. In 2010, similar field tests were performed with both E325ad1 and E325ad2. The relative area under the population curve (RAUPC) for the two mutants did not differ in two field trials. The RAUPC of both mutants was similar to that of the parent strain in one trial and greater (P = 0.05) compared to the parent in another trial. Thus, the mutation resulting in the antibiotic-deficient and rough-colony phenotype of E325ad1 was not detrimental to epiphytic fitness on flowers. In both field and laboratory tests, antibiotic-deficient mutants reduced (P = 0.05) the RAUPC of the pathogen compared to the pathogen RAUPC of water-treated controls in some, but not all, cases. In each experiment, the RAUPC values for Ea153N on flowers treated with E325ad1 or E325ad2 did not differ. The parent strain E325 consistently suppressed growth of the pathogen on flowers, and the level of suppression of the pathogen by E325 was significantly (P = 0.05) greater than that obtained with the antibiotic-deficient mutants. This study provides evidence that antibiosis by E325 is involved in suppression of E. amylovora on flower tissues.