Analysis of Pseudomonas syringae Populations and Identification of Strains as Potential Biocontrol Agents Against Postharvest Rot of Different Fruits

Abstract

A collection of Pseudomonas syringae strains was evaluated for in vitro and in vivo growth inhibition of a broad spectrum of bacteria and fungi, for production of hydrolytic enzymes, presence of syrB gene and for pathogenicity on detached fruits and then they were genetically characterized by ARDRA, ERIC- PCR and fAFLP. P. syringae strains and their culture filtrates inhibited a wide range of phytopath- ogenic bacteria and fungi in vitro and the inhibition depended on the bacterial and fungal strain. The cell-wall degradation enzymes N-acetyl-β-d-glucosaminidase (NAGase), β-glucosidase, cellobiohydrolase, cellulase and protease were detected in culture filtrates of the majority of strains while only a few strains showed chiti- nase and glucanase activities. The antagonistic activity in vivo of P. syringae strains - evaluated on wounded lemon, orange and mandarin fruits against Penicillium digitatum, on apples against P. expansum, on grape berries against Botrytis cinerea - was apparent for some of the strains evaluated. P. syringae strains isolated from Citrus spp., pear and strelitzia were moderately to highly pathogenic on tested detached citrus fruits. All P. syringae strains showed the presence of syrB gene and their molecular characterization with ARDRA, ERIC-PCR and fAFLP allowed their clustering in distinct groups. A partial correlation between groups delineated on the basis of antagonistic activity in vitro and genomic fingerprints was also apparent. Fluorescent AFLP analysis also produced characteristic profiles for each strains useful for risk assessment, monitoring and identification of released antagonistic strains.