Biochemical and physical interactions among Fusarium oxysporum, biocontrol agents and tomato plant roots

Several bacterial strains were isolated from suppressive organic amendments and composts and tested for their ability to inhibit growth of Fusarium oxysporum f. sp. lycopersici (Fol). Four strains that proved to be very effective antagonists were identified as Bacillus spp. (strains BTd43, BO5A and BO7) and Pseudomonas spp. (strain BTd1). The possible physical and biochemical interactions of these selected bacterial strains with Fol hyphae and tomato roots were investigated. Scanning electron microscopy showed that bacterial cells apparently adhere to both pathogen hyphae and tomato roots. Fungal hyphae appeared to be frequently damaged at the fungus-bacterium interfaces. Glucanase and chitinase activities, which are known to degrade of fungal cell wall polymers, were investigated by growing bacterial strains in the presence of Fol cell walls. Enzyme assays of crude protein extracts as well as polyacrylamide gel electrophoresis analyses showed possible induction of proteins with glucanase and chitinase activity by fungal cell walls. The role of these lytic enzymes in the mechanisms of action of the antagonist bacteria and the mutual interaction of biocontrol bacteria with pathogen and host plant are under study.