Eucalyptus globulus Leaf Aqueous Extract Differentially Inhibits the Growth of Three Bacterial Tomato Pathogens.

As available tools for crop disease management are scarce, new, effective, and eco-friendly solutions are needed. So, this study aimed at assessing the antibacterial activity of a dried leaf Eucalyptus globulus Labill. aqueous extract (DLE) against Pseudomonas syringae pv. tomato ( Pst ), Xanthomonas euvesicatoria ( Xeu ), and Clavibacter michiganensis michiganensis ( Cmm ). For this, the inhibitory activity of different concentrations of DLE (0, 15, 30, 45, 60, 75, 90, 105, 120, 135, and 250 g L -1 ) was monitored against the type strains of Pst , Xeu , and Cmm through the obtention of their growth curves. After 48 h, results showed that the pathogen growth was strongly inhibited by DLE, with Xeu the most susceptible species (15 g L -1 MIC and IC 50 ), followed by Pst (30 g L -1 MIC and IC 50 ), and Cmm (45 and 35 g L -1 MIC and IC 50 , respectively). Additionally, using the resazurin assay, it was possible to verify that DLE considerably impaired cell viability by more than 86%, 85%, and 69% after Pst , Xeu , and Cmm were incubated with DLE concentrations equal to or higher than their MIC, respectively. However, only the treatment with DLE at 120 g L -1 did not induce any hypersensitive response in all pathogens when treated bacterial suspensions were infiltrated onto tobacco leaves. Overall, DLE can represent a great strategy for the prophylactic treatment of tomato-associated bacterial diseases or reduce the application of environmentally toxic approaches.