CHARACTERIZATION OF BACTERIAL ANTAGONISTS AND THEIR RESISTANCE INDUCING EFFECT AGAINST BACTERIAL WILT CAUSED BY RALSTONIA SOLANACEARUM IN TOMATO. H. Kurabachew and K. Wydra
Institute of Plant Diseases and Plant Protection, Leibniz Universität Hannover, Herrenhäuser Str. 2, 30419 Hannover, Germany. wydra@ipp.uni-hannover.de.

Abstract: Among 150 bacterial strains isolated from tomato and potato rhizosphere soil from Ethiopia, 15 showed antagonistic activity against R. solanacearum in in vitro tests. Strains were so far identified by fatty acid analysis as Bacillus cereus and Pseudomonas putida biotypes A and B, and characterized by colony morphology, oxidase and catalase test, gelatine liquefaction, levan formation, starch hydrolysis, carbohydrate utilization and growth at different salt concentrations. Key compounds of plant growth promoting (PGP) activity were tested by determination of the production of siderophores, indole-acetic acid and hydrogen cyanide and the ability to solubilize phosphate. The strains were variable in acyl-homoserine lactone (AHLs) production, the common quorum sensing signal, using cross-feeding assays with selected antagonists and the mutant biosensor strain Chromobacterium violaceum CV026. In ad planta tests with 5 antagonists on the moderately resistant tomato genotype King Kong 2 and the susceptible L390, disease severities and incidences were reduced in both genotypes, with a reduction of bacterial multiplication in stems by 16.0%-24.7% and 27.0%-33.6%, respectively, depending on antagonist applied. Split root tests applying the antagonists to one pot apart from the pot with R. solanacearum inoculation confirmed the reduction of disease development and bacterial numbers in antagonist treated plants indicating the induction of a rhizobacteria-induced systemic resistance (ISR). Increases in plant biomass in antagonist-treated plants indicated the plant growth promoting activity of the strains. Enzymatic assays and q-RT-PCR for quantification of key enzymes of signaling pathways are ongoing.