Effects of essential oils, Bacillus amiloliquefaciens and acibenzolar-s-methyl on bacterial wilt incidence and Ralstonia solanacearum populations in tomato plants.

The efficacy of 5 Sardinian essential oils (Helichrysum sp., Mentha piperita, M. pulegium, Myrtus communis, Thymus herbabarona), thymol (Fluka) and Bacillus amyloliquefaciens and a SAR inducer acibenzolar-S-methyl in vitro and on tomatoes plants grown in greenhouse for control bacterial wilt was evaluated. The soil was first infested with a mixture of an equal amounts of two virulent Rs strains. After 1h of incubation, essential oils and thymol were incorporated into soils. In order to evaluate antagonistic activity of B. amyloliquefaciens, the suspensions of Rs were incorporated into soil 24 h after the antagonist. Acibenzolar-S-methyl was applied on tomato plantlets as a foliar spray at a concentration of 25 mg/l before transplanting and increased to 50 mg/l after transplanting. The trials were repeated twice. Seven days after essential oils treatments, Rs populations density were determined on SMSA. Wilted plants and latent infection, detected by direct isolation and ELISA, were determined one month after transplanting. Bacterial wilt incidence and Rs concentration, compared with control, were reduced considerably on tomato plants transplanted in soil treated with 1g/l of essential oils, thymol and B. amyloliquefaciens. However, the effectiveness of oils and thymol was reduced when application rates were lowered (0,5g/l). At two concentrations (0,5 and 1g/l), significantly more wilt occurred in tomato plants grown in soil treated with M. piperita oil. Plants treated with acibenzolar-S-methyl were apparently healthy. Tests revealed that all plants were systematically infected by Rs. The possibility to test essential oils, together with antagonists and SAR inducers are now in progress.