Molecular approaches to improve biocontrol of soil-borne fungal pathogens

The highly toxic and climatically relevant soil fumigant methyl bromide was used to suppress soil-borne pathogens, which cause high yield losses world-wide. To develop environmentally friendly alternatives in plant protection, two target pathogens with a broad host range and high economic importance were studied: Verticillium dahliae Kleb. and Rhizoctonia solani Kühn. Strategies to select the most efficient antagonists were developed on the basis of hierarchical systems combining microbiological, molecular and phytopathological methods. To control Verticillium wilt, the biocontrol agent (BCA) Serratia plymuthica HROC48 was selected. The strain shows high antifungal and plant growth promoting activity and posses no risk for the environment and human health. RhizoStar® is registered and produced by E-nema, Raisdorf, Germany. For a biocontrol of Rhizoctonia diseases another strategy was developed: a combination of fungal and bacterial antagonists has been applied. While the fungi are used for direct disease protection and parasitism of sclerotia and hyphae, endophytic bacteria are applied to enhance plant growth and protect against the pathogen from outside and inside the rhizosphere. The mode of action of BCAs and of interaction with microbial community was studied using molecular and microscopic techniques (FISH in combination with Confocal Laser Scanning Microscopy). Results of these investigations lead to new strategies in application and formulation of BCAs.