Natural Bactericidal Effects of Psoralea glandulosa Essential Oil for the Control of Bacterial Canker and Speck in Tomato

Bacterial canker and bacterial speck are diseases affecting tomato caused by Clavibacter michiganensis subsp. michiganensis and Pseudomonas syringae pv. tomato, respectively. These diseases are considered a serious threat with a strong impact on tomato production and marketing worldwide, especially because of their reduced sensitivity to traditional controls. This work reports the chemical composition of the essential oil (EO) of Psoralea glandulosa and investigates its in vitro antimicrobial activity, along with its main compound, against three strains of Clavibacter michiganensis subsp. michiganensis (CmVC533, CmVLC78, and CmVQ59) and one strain of Pseudomonas syringae pv. tomato (Pst). The results indicate that both the EO and bakuchiol have significant antibacterial capacity, especially the EO, which reaches a minimum inhibitory concentration (MIC) between 4–16 µg/mL and 128 µg/mL, and a minimum bactericidal concentration (MBC) between 8–16 µg/mL and 128 µg/mL for the strains of C. michiganensis subsp. michiganensis and P. syringae pv. tomato, respectively. The EO and bakuchiol also had an inhibitory effect when applied directly onto plates seeded with C. michiganensis subsp. michiganensis. Overall, the results from this study should be verified in the near future by in vivo studies.