Endophytic survival of Pseudomonas syringae pv. actinidiae in Actinidia chinensis 'Hort16A' plants

To tackle the epidemiological role of the latency phase of Pseudomonas syringae pv. actinidiae (Psa) in susceptible asymptomatic host plants, the pathogen survival and colonization were studied in seven-year-old plants of Actinidia chinensis ‘Hort16A’. The plants were inoculated with a virulent Psa gfp-expressing/rifampicin-resistant strain (Psagfp-Rifres) and the endophytic presence of Psa was determined by analysis of the whole plants to re-isolate Psagfp-Rifres and by PCR assays to confirm identity. Finally, the isolates were tested to verify their ability to induce disease symptoms and HR respectively in host and non-host plants. The Psagfp-Rifres presence inside the tissues of the experimentally contaminated plants was detected during the years following the inoculation. The data obtained showed that systemic colonization of host tissues by Psagfp-Rifres took place for a long period of time. The epidemiological significance of this finding raises questions about the effectiveness of the control measures to prevent bacterial canker solely based on antimicrobial treatment on plant surfaces.