Activity of the microbial control agent Bacillus subtilis strain QST 713 against bacterial canker of kiwifruit

Bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), became relevant, especially in 2008 and 2009. Epidemics occurred in Lazio and Emilia Romagna (central and northern Italy) and the causal organisms were identified on the basis of phenotypic and genomic characteristics. In Italy, the control of bacterial canker relies mainly on agronomic prophylactic measures and on the use of copper-based products. In this study, we investigated the ability of Bacillus subtilis strain QST-713 (Serenade Max) to inhibit the growth of two different Psa strains in vitro, and its ability to survive and reduce the population of two rifampicin resistant pathogen strains on female flowers of Actinidia chinensis and A. deliciosa. The microbial control agent was able to survive on female flowers of both Actinidia species, reaching a population of ca. 105 CFU/flower 48 and 96 h after application. Moreover, the antagonist reduced the Psa population on A. chinensis flowers by more than one order of magnitude 48 h after its application. These preliminary results indicate that B. subtilis strain QST 713 may be a promising tool for the biological control of bacterial canker of kiwifruit, and provide insights into the interaction between the microbial control agent and Psa.