Rhizobacteria isolated from common bean in southern Italy as potential biocontrol agents against common bacterial blight

Common bacterial blight, caused by Xanthomonas axonopodis pv. phaseoli and its variety fuscans, leads to important crop loss and, due to limited bactericides availability and effectiveness in agriculture practices, it appears necessary to develop alternative control strategies. The aim of this study was to assess the potential of bacteria isolated from bean rhizosphere to control the above mentioned disease. Sixty out of 162 bean rhizobacteria inhibited the growth in vitro of selected virulent strains of both varieties of X. a. pv. phaseoli and, when applied to seeds before sowing, six of them reduced disease symptoms on bean in in vitro and greenhouse pathogenicity assays. In order to deepen bacteria characterization, the six rhizobacteria were evaluated for lytic enzymes, hydrogen cyanide, ammonia, siderophores, indoles production, for inorganic phosphates solubilisation and environmental adaptability in terms of salinity, pH and temperature gradients variation. Altogether the findings of this study indicate the above six rhizobacteria as potential biocontrol candidates.