ELICITATION OF RESISTANCE TO FIRE BLIGHT BY A MICROBIAL CONSORTIUM: SEARCH FOR AN EVIDENCE THROUGH A TRANSCRIPTOMIC APPROACH

Fire blight is the most destructive bacterial disease of pome fruits: it is caused by Erwinia amylovora and its management remains cumbersome. Nowadays, treatments with several beneficial microorganisms can lead to an affective integrated pest management (IPM): nevertheless, their specific activity in enhancing plant defence mechanisms is only partially understood. An extensive 3-years study in a commercial pear orchard was carried out, to verify the efficacy of a commercial microbial consortium (Micosat F®, CCS Aosta srl, Italy) to control a fire blight outbreak. In parallel, we have used a dHPLC (denaturing High Performance Liquid Chromatography) and automated DNA fragment collection using the WAVE System to analyse and recover cDNA-AFLP fragments. This transcriptomic approach was applied to understand which complex transcriptional changes these microorganisms may have elicited in the plant-pathogen interaction. In the commercial orchard, the beneficial effects of microbial consortium were confirmed by a significant disease reduction starting from the first year of application, as compared with other treatments commonly used by orchardists in IPM strategies. Among the eighty-five transcriptderived fragments (TDFs) collected and identified through the cDNA-AFLP-dHPLC approach, fourteen were found involved in systemic acquired resistance (SAR) according to the available literature. The transcriptomic approach developed in this study has been a robust and user-friendly mRNA fingerprinting method for the identification of differentially expressed genes, where prior knowledge of specific gene sequences is not a prerequisite. Finally, we confirmed the activity of such the microbial consortium as resistance inducer.