|Stockwell, V - OREGON STATE UNIVERSITY|
|Johnson, K - OREGON STATE UNIVERSITY|
Submitted to: Biological Control of Fungal and Bacterial Plant Pathogens Working Group
Publication Type: Proceedings
Publication Acceptance Date: September 26, 2008
Publication Date: N/A
Technical Abstract: Adoption of bacterial antagonists for disease management is hampered by inconsistent performance. Intergeneric mixtures of antagonists may reduce variation in control by establishing a robust community on plant surfaces and greater competition to the pathogen during its critical epiphytic growth stage. Pseudomonas fluorescens A506 and Pantoea agglomerans Eh252, bacterial antagonists for the management of fire blight of pome fruit trees, are examples of ecologically-compatible bacterial antagonists. A506 suppresses colonization by the pathogen by competitive exclusion. Strains of P. agglomerans, such as Eh252, suppress pathogen growth by competition and production of an important small peptide antibiotic. When applied in a 1:1 mixture, A506 and Eh252 often established greater population sizes on plant tissues; however, disease control was not significantly improved by the mixture compared to single strains. In laboratory assays, we found that A506 produced an extracellular metalloprotease that detoxified the peptide antibiotic of Eh252. We attribute the lack of synergism of the two strains in disease control to ‘mechanistic incompatibility’ or the interference in antibiosis by Eh252 by the protease of A506. We selected a Tn5 mutant of A506 deficient in production of the extracellular protease. The protease-deficient mutant colonized plant tissues and provided similar levels of disease control as wild-type A506. Combining the protease-deficient derivative of A506 with Eh252 increased disease control to levels that are significantly greater than single strain inoculants. Altering A506 to be mechanistically compatible with its co-inoculant Eh252 improved disease suppression and decreased variability in biological control of fire blight.