First attempts to obtain Actinidia deliciosa plants inoculated with endophytes antagonistic against Psa

Severe outbreaks of bacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae (Psa) have been reported in Veneto and Friuli Venezia Giulia (north-east Italy) since 2010-2011. Since in some orchards with severe epidemics of Psa some Hayward plants were less affected by Psa, we carried out a study aiming at the selection of potential biocontrol agents (BCAs). From asymptomatic plants a bacterial strain 4A7 closely related to Pseudomonas asplenii was isolated and demonstrated in vitro antagonistic activity against Psa. In this study P. asplenii 4a7 (Pa4A7) was used for inoculation of micro-propagated plantlets 'Hayward' to obtain propagated material containing the antagonistic endophyte. To confirm the success of Pa4A7 inoculation in micro-propagated plants, we developed a specific and sensitive molecular method for its detection and quantification. The presence of Pa4A7 has been confirmed up to 100 days from the beginning of the test. This work represents the first step in trying to obtain plants with characteristics of tolerance to the pathogen based on inoculation of antagonistic endophytes.