Selection of biological control agents against the pathogen Pseudomonas syringae pv. actinidiae from phyllosphere of kiwifruit leaves

Pseudomonas syringae pv. actinidiae (Psa) is the causal agent of bacterial canker, the most devastating disease of kiwifruit. The control of this disease is still challenging since it relies primarily on the use of copper-based pesticides and plant-resistance inducers. The recent restrictions in the European regulations on chemical pesticide, together with the rising interest of the public opinion on sustainable production methods, organic agriculture and environment-friendly pest and disease control, led to development and optimization of methods based on biological control agents (BCAs) in fruit production. However, the efficacy of BCAs has often resulted erratic thus limiting their adoption in commercial horticultural production. The selection of beneficial microorganisms directly from the phyllosphere of the host plant is a promising approach to overcome this limitation. This work aimed at screening the kiwifruit epiphytic microbiome from three infected orchards in Portugal to identify bacterial candidates able either to directly inhibit or to interfere with Psa growth, to be used for the biological control of Psa. Strains of Pseudomonas putida and Pseudomonas poae were found to efficiently antagonize Psa on flowers (reduction from 10(7) to 10(4) CFU mL(-1) in 24 h), and colonized all susceptible organs with high surviving rates in greenhouse conditions. BCA candidates will also be evaluated for their ability to promote plant growth or induce plant resistance. These results open new perspectives for developing commercial product based either on single bacterial strain or multiple bacteria with complementary mode of action, with high efficiency in colonizing the host plant.