Enhancement of PR1 and PR5 gene expressions by chitosan treatment in kiwifruit plants inoculated with Pseudomonas syringae pv. Actinidiae.

Kiwifruit, with a production of more than 1.5 million tons/year in the world, must be protected against attack by its most common pathogen. Following the European guidelines on the substitution of pesticides by safer alternatives, the aim of this work was to verify if kiwifruit plants are able to better resist pathogen infections through the use of chitosan, a biodegradable compound and a well-known elicitor of Systemic Acquired Resistance (SAR). To evaluate the chitosan’s elicitation effect in plant during the treatment period, two genes involved in the metabolic pathway of SAR were chosen, Pathogenesis Related Protein 1 and 5 (PRs). Primers for both genes were designed and validated and chitosan’s elicitation effect was tested in qRT-PCR. Elicitation of SAR was first evaluated in a model system with plants cultured in vitro and subsequently in 2 year old plants belonging to two different species (Actinidia chinensis Planch. and A. deliciosa (A. Chev.) C.F. Liang & A.R. Ferguson). To evaluate the effects of chitosan elicitation in the presence of the pathogen attack, the 2-year-old plants were inoculated with the bacterium Pseudomonas syringae pv. actinidiae. Micropropagated kiwifruit plants were a good model to test molecular markers for SAR onset. Moreover, PR1 and PR5 have also shown to be suitable candidates for the detection of the plant immune system activation. In this study, chitosan elicited a systemic response in kiwi plants with intensity comparable to other well-known signalling compounds (salicylic acid, methyl jasmonate or ethylene), as shown by the changes in PR1’s and PR5’s transcription profiles. The data obtained by chitosan treatments in in vitro cultures were confirmed in plants grown in greenhouse, in which, moreover, the combination of chitosan treatment and the bacterial inoculum had the greatest effect on PRs synthesis. This study also proved that chitosan, leading to an increased expression of both PRs, has a role in kiwifruit defense reactions.