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.