Characterization of Chilean Pseudomonas syringae pv actinidiae strains isolated from infected orchards

Abstract

Pseudomonas syringae pv. actinidiae (PSA) strain is a major problem for the kiwifruit industry worldwide. So far, 5 biovars of PSA have been identified, of which the most virulent form is biovar 3. This is the only biovar that has been detected in Chile, which is the third kiwifruit exporter country and is currently suffering from canker disease produced by PSA. Single nucleotide polymorphisms (SNPs) analyses have classified the biovar 3 strain into three groups: the European, the New Zealander and the Chilean groups, which have evolved from a common Chinese PSA ancestor. Although Chilean strains have been used in phylogenetic analysis, there is no information about genomic diversity within this group or whether they present microbiological characteristics that could affect its virulence. In this work we studied 15 Chilean bacterial isolates collected from orchards with canker disease symptoms, and classified them as PSA using a different PCR techniques. To gain more information on the relationship between the isolates we sequenced part of three conserved genes widely used to classify bacterial strains: gtl (Citrate Synthase), rpoD (Sigma subunit of RNA polymerase II) and gyrB (Gyrase B). Using these sequences we performed a phylogenetic analysis that included some PSA reference sequences. Fourteen PSA Chilean isolates were grouped with PSA reference strains and three of them formed a subgroup within the PSA clade, suggesting clear differences at the genomic level among the isolates. We evaluated three microbiological traits in all the isolates: motility (swimming and swarming), and ability to induce a hypersensitive response in tobacco plants. All the isolates were able to induce the hypersensitive response in tobacco plants and were also able to perform both types of movements in appropriated growing conditions. PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.2787v1 | CC BY 4.0 Open Access | rec: