Preliminary characterization and mode action of Pseudomonas synxantha DLS65 as the active ingredient of Microfighter, an innovative biopesticide

The everyday use of copper-based pesticides in agriculture resulted in its accumulation in the agro-environment, thus posing a threat to its safety, human health, and biodiversity. Effective alternatives are being investigated, and using ben¬eficial microbes is a promising approach to reduce the use of copper. The EU-financed project “LIFE Microfighter” is currently checking the efficacy of Pseudomonas synxantha, strain DLS65 (DLS65), coupled with natural zeolites, to lower the impact of fungal (grapevine downy mildew) and bacterial (olive knot and tomato speck) diseases, together with the reduction of copper inputs in vineyards, olive groves, and tomato fields. DLS65 showed tolerance to cop¬per (500 ppm) in liquid and solid medium, thus confirming its viability and activity in IPM strategies with reduced cop¬per use: such tolerance was molecularly confirmed through the detection of the cusABL genes cluster. Traits linked to a plant growth promotion activity by DLS65 were observed, demonstrating its ability to produce siderophores, ammo¬nia, and solubilize phosphates. The antimicrobial activity of DLS65 appears to be linked to the production of volatile organic compounds (VOCs), since the growth and virulence traits of Pseudomonas syringae pv. tomato and Pseudo-monas savastanoi pv. savastanoi were severely affected. Finally, DLS65 coupled with natural zeolites, reduced the incidence of grapevine downy mildew in semi-field experi¬ments, although its control mechanism(s) remain largely unknown. Our findings confirmed strain DLS65 as a promis¬ing biocontrol agent against both bacteria and the oomycete. Research funded by the European Commission under the LIFE21-ENV-IT-LIFE MICROFIGHTER project, Grant Agreement N. 1010742018.