Efficacy of phosphate-mobilizing bacteria to control plant pathogens in tomato when applied with an animal bone charcoal formulation

The aim of this research is recycling of high phosphorus containing organic waste from food industry (bone meal) into a safe biotechnological crop protection and plant fertilizer product. Carbonization of animal bone meal generates a porous product, which is suitable for microbial colonization. This animal bone charcoal (ABC) can be used as microbiological carrier for biological control agents or other beneficial micro-organisms, meanwhile delivering P for plant growth. Several naturally occurring soil bacteria with antagonistic properties were able to solubilise phosphate: e.g. strains of Burkholderia, Pseudomonas, Serratia, Bacillus, Paenibacillus, Arthrobacter, and Streptomyces. These bacteria were further tested for their capability to colonize the bone char with an additional carbon source, and to survive in the dried product. Few promising bacterial isolates were further tested for biocontrol efficacy in plant assays in the greenhouse. Tests were performed with young tomato plants in potting soil and rockwool, which were infested with Pythium aphanidermatum and Fusarium oxysporum f.sp. radicis-lycopersici (FORL) causing respectively damping off and crown and root rot. Scanning electron microscopy (SEM) pictures showed the intensive colonization of the bacteria in the interior of ABC. Of the tested strains, Pseudomonas chlororaphis 4.4.1 was most effective in controlling the diseases; it controlled P. aphanidermatum and FORL in tomato in each of the tests. Meanwhile, the strain appeared to be a very good root colonizer; 1-8% of the cultural bacteria on the roots or in rhizosphere soil consisted of the introduced strain.