Archivio Journal of Plant Pathology

Abstract:

A set of bacterial isolates originating from tomato rhizosphere was screened for their potential to inhibit the growth of Pseudomonas syringae pv. syringae and Pseudomonas syringae pv. morsprunorum. Isolates P482, P487, T660 and T777 showed the greatest antagonism towards the majority of the tested pathogenic isolates and therefore were selected for further studies. These strains were tentatively identified as Pseudomonas fluorescens (T660 and T777) and Pseudomonas putida (P482 and P487) on the basis of the 16S rDNA sequence analysis. The synthetic peptide CAMEL, an antagonistic factor with proved antimicrobial activity was also tested. The determined value of the minimal bactericidal concentration (MBC) of CAMEL was 1.6 μM towards 5 strains each of both P. syringae pathovars. CAMEL did not influence the growth of the antagonists in concentrations of up to 3.4 μM, therefore a possible synergistic activity of the antagonists and CAMEL towards the tested pathogens was investigated. To this end, spontaneous rifampicin- resistant mutants of the antagonists were selected. The MBC value of CAMEL used against the tested pathogens decreased to 1.13 μM when P. fluorescens T660 was applied simultaneously with the peptide. The selected antagonistic Pseudomonas sp. strains, CAMEL, or the combination CAMEL/P. fluorescens T660 could potentially contribute to the management of P. syringae infections in stone fruit trees based on enhanced antagonistic activity in vitro. Field studies are necessary to substantiate this postulate.