Endophytes-a source for biological control agents

Plants are strongly associated and influenced by microbes. The composition of bacterial communities from different plant microenvironments (phyllosphere, endosphere, rhizosphere and endorhiza) of field-grown potato was studied using a multiphasic approach including cultivation dependent and independent analysis. In vitro dual culture assay was used for determination of the antagonistic potential of potato associated-bacteria against the important soil-borne pathogens Verticillium dahliae and Rhizoctonia solani. Interestingly, results revealed that composition and diversity of bacterial antagonists were mainly specific for each microenvironment. The main reservoir for antagonistic bacteria was the rhizosphere and the endorhiza. They were characterized by a highly similar composition of bacterial populations. Nearly identical fingerprints for the most prominent species Pseudomonas putida isolated from these micro-habitats confirmed the sharing of populations. Endophytes with antagonistic activity were mainly characterized as species belonging to Pseudomonas, Bacillus, Agrobacterium and Serratia. Endophytic bacterial isolates for biocontrol potential were evaluated on target-specific fungal antagonism and physiological characteristics. The endophyte Serratia plymuthica 3Re4-18 showed high inhibition effects against various pathogenic R. solani isolates. This strain is a competent root colonizer, which was analyzed using gfp-labeled mutants by confocal laser scanning microscopy. The high rhizosphere competence as a key factor for a successful disease suppression in the field was independent of the soil type and the crop species. The …