Activity against Fusarium oxysporum of antagonist bacteria isolated from suppressive soils or composts

The most common approach to biological control involves selection of antagonist microorganisms, elucidation of their modes of action, optimization of the antagonistic activity and development of biocontrol products. The rate of suppressiveness of composts and natural amendments against soil-borne pathogens (Fusarium oxysporum, Phytophthora spp., Pythium spp., Rhizoctonia solani, Sclerotinia spp., Sclerotium rolfsii, Verticillium dahliae, and others) depends on several characteristics of these substrates such as chemical components, composting conditions and microorganic components. Among microorganisms populating different composts and amendments, over 130 bacterial strains were isolated and assayed in vitro for their antagonist activity against F. oxysporum f.sp. lycopersici. Some of the most effective antagonists were studied for their in vitro and in vivo interaction with both pathogen and roots of tomato plants. Results of these investigations showed that 26 bacterial strains inhibited the radial growth of F. oxysporum on agarized medium; moreover, on liquid medium, bacterial culture filtrates reduced both germination and germ tube-elongation of fungal spores. Scanning electron microscopy observations of two antagonist bacteria showed that bacterial cells adhere to F. oxysporum hyphae causing collapse of the fungal cell wall. This research gives useful information to optimize the activity of biocontrol bacteria in order to develop new and high effective bioformulates for use in eco-compatible agriculture.