Screening of microbial biocoenosis of Actinidia chinensis for the isolation of candidate biological control agents against Pseudomonas syringae pv. actinidiae

The present study aimed to isolate and characterize candidate biological control agents against Pseudomonas syringae pv. actinidiae (Psa), the causal agent of kiwifruit bacterial canker. Biological control represents a promising strategy to reduce or complement the use of chemical pesticides. In the case of Psa, the common preventive strategies rely on the use of copper formulations. However, the use of copper has some severe limitations because of environmental concerns, phytotoxicity and the possible development of bacterial resistance. The use of copper is particularly hazardous during blooming, which is a phenological phase with a high risk of Psa infection. Therefore, the use of a biological control agent, especially selected to be active in this phenological phase, is an interesting control alternative. Bacterial biocoenosis, naturally present on flowers, was screened to identify species able to effectively reduce infection at blooming. Flowers from both Actinidia deliciosa and Actinidia chinensis were sampled in healthy and infected orchards, and culturable microorganisms were isolated and tested against Psa both in vitro and in planta. Among the 78 isolates, only two, belonging to Pseudomonas fluorescens, were able to inhibit Psa growth in vitro and to reduce disease incidence in planta. Further experiments will be performed in order to confirm these preliminary results and to optimize the use of candidate biocontrol agents under real conditions