COMPATIBILITY OF BACTERIAL ANTAGONISTS WITH STREPTOMYCIN AND OXYTETRACYCLINE

In field experiments, bacterial antagonists that suppress fire blight, Pseudomonas fluorescens A506 (resistant to streptomycin, Sm, and oxytetracycline, Tc) and Erwinia herbicola C9-1Sm^r (Sm-resistant but Tc-sensitive), were sprayed onto apple at 30–50% bloom.
Water, Sm (Agrimycin D, 100 μg/ml), and Tc (Mycoshield, 200 μg/ml) were applied 3 and 7 days later.
Populations of A506 and C9-1Sm^r on stigmas of individual blossoms were estimated before and after sprays to evaluate the effect of the antibiotics on colonization of blossoms by the antagonists.
Populations of both A506 and C9-1Sm^r averaged 10⁵ cfu/blossom on the majority of blossoms on water-treated trees.
Sm sprays did not adversely affect colonization of blossoms by A506 or C9-1Sm^r. The early application (3 d after inoculation) of Tc decreased the average populations of A506 and C9-1Sm^r by 1 log unit and also decreased the proportion of blossoms from which the antagonists could be recovered.
In contrast, late Tc sprays (7 d after inoculation) had only slight effects on colonization by the antagonists.
For comparison, colonization of blossoms by Erwinia amylovora 153 (sensitive to Sm and Tc) was decreased by antibiotic sprays to a greater magnitude than were the antagonists.
These results indicate that antibiotic sprays can be used with A506 and C9-1Sm^r; although for optimal integration, application of Tc should be delayed until after the antagonists are established on blossoms.

VII International Workshop on Fire Blight

V.O. Stockwell, J.E. Loper, K.B. Johnson

https://doi.org/10.17660/ActaHortic.1996.411.65