Combination of copper with Lysobacter capsici AZ78: towards new strategies for the biological control of Plasmopara viticola

Downy mildew is an important grapevine disease caused by the oomycete P. viticola, a biotrophic microorganism able to attack all green parts of grapevine plants. The control of downy mildew mainly relies on the frequent application of copper based fungicides. Growing concerns about the impact of copper and pesticides on the agricultural soils and environment is prompting the selection of new microorganisms that can effectively control P. viticola. No studies exist regarding the possibility of combining bacterial strains with copper. For the first time we show that resistance to copper is a trait shared by Lysobacter species and associated with the presence of genes coding for copper oxidase (copA) and copper exporting PIB-type ATPase (ctpA). We have demonstrated that resistance to copper in L. capsici AZ78 allows this bacterial strain to be applied with low doses of a copper-based fungicide and this combination led to an increase in the efficacy of grapevine downy mildew control. Resistance to copper allowed L. capsici AZ78 to be combined with a low-dose of a copper-based fungicide, leading to more effective control of grapevine downy mildew. The information coming from the sequencing of the genome of L. capsici AZ78 confirm that this bacterial strain can be combined with copper based fungicides and this possibility is deriving from the presence of genes involved in the transport, homeostasis, uptake and resistance to copper ions Interestingly, the RAST analysis evidenced that the genome of L. capsici AZ78 include several genes deputed to the resistance to arsenic, cadmium, cobalt and zinc.