Biological plant protection using rhizobacteria - an environmental friendly alternative for biological control of soilborne and seedborne phytopathogenic fungi.

摘要

The biological control agents (BCAs) Pseudomonas spec. L29-1-8, Serratia plymuthica DSM 12502, Streptomyces spec. 12424 and Streptomyces albidoflavus DSM 12500 were isolated from the rhizosphere of different crop plants, Pseudomonas spec. L29-1-8 from the rhizosphere of potato, Serratia plymuthica DSM 12502 from the rape rhizosphere and Streptomyces spec. 12424 and Streptomyces albidoflavus DSM 12500 from the rhizosphere of strawberry. The isolates were identified using morphological, physiologicaland molecular methods. On genera level the strain L29-1-8 was identified by FAME-analysis, BIOLOG and sequencing of the 16S rDNA as Pseudomonas spec. and the strain DSM 12424 as Streptomyces spec. by morphological characterization and 16S rDNA sequencing. On species level the strain DSM 12500 was identified using phenotypical characterization as Streptomyces albidoflavus and the strain DSM 12502 as Serratia plymuthica by API-System, BIOLOG and comparison of 16S rDNA-sequence with the Serratia plymuthica type strain DSM 4540. Genotypic diversity among the isolates compared with other plant-associated isolates of the same species or genus was characterized by molecular fingerprinting methods using BOX-PCR and macrorestriction of genomic DNA and electrophoretic separation of DNA fragments by pulsed-field gel electrophoresis (PFGE). Because of their unique fingerprints the biological control agents could be differentiated from other rhizobacteria of the same species or genus. The BCAs were characterizedregarding their antagonistic properties. All investigated isolates showed an in vitro antagonism toward several fungal pathogens investigated by dual culture assay. Mechanisms of fungal inhibition were elucidated by tracing secondary-metabolite production and fungal cell wall-degrading activity. The streptomycetes DSM 12424 and DSM 12500 produced siderophores and antibiotics. Chitinolytic activity was measured by the Serratia plymuthica DSM 12502 and the streptomycetes. The production of plant growth promoting substances (plant-growth hormone indole-3-acetic acid) was proved for all strains and led to increased emergence rate and an improved growth and health of treated plants. The bacteria were able to suppress plant pathogenic fungi in different pathosystems (e. g., sugar beet -- Rhizoctonia solani, sugar beet -- Pythium ultimum, strawberry -- Verticillium dahliae, lambs lettuce -- Phoma valerianellae, cress and parsley -- Alternaria spec.). The Streptomyces spec. strain DSM 12424 was patented in Germany. The strain was formulated as water dispersable granules containing spores and mycelium and was called Rhizovit(R). For the isolates DSM 12500 (Streptomyces albidoflavus) and 12502 (Serratia plymuthica) patented as BCA-strains in Europe and USA andfor the Pseudomonas spec. strain L29-1-8 a formulation is developing. The product Rhizostar(R) based on the strains DSM 12500 and DSM 12502 and the product Rhizovit(R) is evaluating i n agricultural practice.