Abstract

Bacterial speck (Pseudomonas syringae pv. tomato) is considered one of the major diseases of tomato crop worldwide and alternative methods to control it are desirable. The objective of this study was to evaluate the effect of essential oils (EOs) on P. syringae pv. tomato strain ufv-1 growth, in controlling bacterial speck in tomato plants, as well as to find the best application time of the EOs. The EOs used in this study were thyme (TH), eucalyptus (EU), tea tree (TT), clove (CL), cinnamon (CN), citronella (CI), and lemon grass (LE). An in vitro test using EOs were conducted to verify the ufv-1 inhibition, and two tests were carried out in a greenhouse to evaluate the effect of EOs before and after inoculation with Pst. Inhibition zones were observed for EU, CI, CL, and CN at a concentration of 1%. Plants pre-treated with EOs showed lower disease severity than that in plants post-treated with EOs (P<0.05), whereas higher efficacy was observed using acibenzolar-S-methyl and CI (91 and 83%, respectively). Regarding post-treatment, TT, TH, CI, EU, LE, and commercial fungicide, resulted in reducing disease severity by 8 to 40% compared to control (water). Results from this study showed the potential use of EOs in controlling bacterial speck in tomato and suggest the induced resistance as the major mode of action.

Key words: Pseudomonas syringae pv. tomato, tomato diseases, alternative control of plant diseases, Solanum lycopersicum.