In vitro and in vivo antibacterial activity of selected essential oil components against Pectobacterium carotovorum subsp. carotovorum and Pectobacterium atrosepticum causing bacterial soft rot of potato tubers

Abstract

Pectinolytic bacteria cause bacterial soft rot of potato tubers. The most significant losses occur during storage. The efficacy of essential oil (EO) components carvacrol, cinnamaldehyde, d-carvone, l-menthone, R-(+)-limonene and thymol was tested against Pectobacterium carotovorum subsp. carotovorum (Pcc) and Pectobacterium atrosepticum (Pa). Disc diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) tests were performed in vitro, as well as potato disc and whole tuber maceration tests in vivo. Under in vitro conditions, cinnamaldehyde was the most effective against both bacteria (MIC 0.5 μL/mL, MBC 1.5 μL/mL). Both bacteria were found to be more susceptible to d-carvone (MIC 1.5-2.5 μL/mL, MBC 2.5 μL/mL) and thymol (MIC 2.5-5 μL/mL, MBC 3-5 μL/mL). R-(+)-limonene was the least effective. Results from the potato tuber disc maceration test confirmed a significant antibacterial effect of cinnamaldehyde at a concentration of 1.5 μL/mL. No rotted area was observed on potato tuber discs after treatment with l-menthone at concentrations of 2.5 μL/mL and 10 μL/mL against Pcc. A more pronounced effect was obtained when carvacrol was used at concentrations of 5 μL/mL against Pcc and 10 μL/mL against Pa. Disease severity tests on potato tubers after soaking for 20 min at MIC concentration of the EO components followed by 7 days of incubation at room temperature and 15 oC confirmed the antibacterial activity of cinnamaldehyde (0.5 μl/ml), l-menthone (2.5 μl/ml) and carvacrol (5-10 μl/ml). Cinnamaldehyde, l-menthone, and carvacrol may be recommended for further testing to treat stored potato tubers.