Modification of the phyllosphere bacterial biocoenosis by Pseudomonas syringae pv. actinidiae infection

In Italy, since 2008, kiwifruit growing has been widely affected by the bacterial pathogen Pseudomonas syringae pv. actinidiae (Psa), the causative agent of bacterial canker. Although the role played by phyllosphere bacteria in protecting hosts against pathogen infection is known, to our knowledge, no studies aimed at characterizing the bacteria living on the aerial parts of the kiwifruit have been performed to date. In the present study, the bacterial communities harbored by flowers of Actinidia chinensis and Actinidia deliciosa are described at both qualitative and quantitative levels. The microbiota of the two kiwifruit species were analyzed in healthy plants and plants infected with Psa. To achieve this goal, a metagenomic approach was adopted, based on deep sequencing of DNA from epiphytic bacteria followed by the amplification of the V3-V4 region of the 16S rRNA gene. In this study, we describe (i) the different composition of the biocoenosis associated with the two main commercial species of Actinidia, (ii) the influence of Psa population on the composition of the epiphytic biocoenosis, and (iii) the abundance and persistence of non-pathogenic bacterial species of interest.