Greenhouse assays on the control of the bacterial canker of kiwifruit (Pseudomonas syringae pv. actinidiae)

BACKGROUND: Pseudomonas syringae pv. actinidiae (Psa) is the etiologic agent of the bacterial canker of kiwifruit, the most severe disease of Actinidia spp. This pathogen was firstly recorded in Japan and in China. The initial occurrence in Italy dates back to 1992, but the most important outbreak was in 2008. From that year, Psa has spread worldwide with a devastating virulence causing substantial losses to kiwifruit production in China, Italy, New Zealand, Chile, France and Portugal. OBJECTIVE: Screening the existing compounds with different mode of action for their efficacy in controlling Psa on Actinidia deliciosa (cv. Hayward) grown in controlled conditions. METHODS: Products were grouped according to their active ingredients and mode of action in the following categories: Copper compounds, plant extracts, disinfectants, resistance inducers, filming agents and biological control agents (BCAs). The experiments were performed on potted A. deliciosa (cv Hayward) vines grown in controlled greenhouse conditions. Inoculation was experimentally performed by spraying each plant till run off with a suspension of a highly virulent, biovar 3 Psa strain. Disease control and phytotoxicity were monitored for 15 and 30 days after inoculation. RESULTS: Copper compounds and resistance inducers (acibenzolar-S-methyl, Fosetyl-Al) showed the most promising results. However, few other compounds, such as some plant extracts and disinfectants (Verdeviva), provided some protection. Also biological control agents (BCAs), containing living microorganisms, partially controlled the disease. CONCLUSION: Copper compounds and resistance inducers can be possibly combined to develop a more robust and effective control strategy in open field. In addition, BCAs seem interesting, particularly in specific phenological stages when other control methods cannot be used, although results require further validation.