Zuckerrübe - Innovative biologische Strategien zum Schutz der Zuckerrübe vor Rhizoctonia solani

To study the microbial communities in different sugar beet-associated microhabitats with special focus on antagonists towards plant pathogens, the composition of microorganisms isolated from the rhizosphere, phyllosphere, endorhiza and endosphere of field grown sugar beet plants was analysed by a multiphasic approach at three different plant developmental stages on six locations in Europe. Analysis of microbial communities by Single Strain Conformation Polymorphism of 16S/18S rRNA clearly revealed the existence of discrete microenvironment-specific patterns. A total of 1,952 bacterial and 1,344 fungal isolates screened by dual testing for antagonism towards the fungal pathogens Aphanomyces cochlioides, Phoma betae, Pythium ultimum, and Rhizoctonia solani resulted in 885 bacterial (=45%) and 437 fungal (=33%) antagonists. In general, the indigenous antagonistic potential was very high and influenced by i) the pathogen, ii) the location, iii) the plant developmental stage, iv) the microenvironment, and v) the cultivar. We showed for the first time that the antagonistic potential was strongly influenced by the target pathogen. The majority of antagonistic microorganisms showed a specific suppression of only one pathogen (bacteria: 664 = 75%; fungi: 256 = 59%) wheras only a few showed a broad host range (bacteria: 4 = 0.5%; fungi: 7 = 1.6%). The bacterial communities harbour the highest antagonistic potential against P. ultimum whereas the fungal communities contained more antagonists against A. cochlioides and R. solani. The endorhiza and endosphere were the main reservoir for antagonistic bacteria. In contrast to the high proportion only a low diversity of antagonists genotypic and species level was found.