Control of the bacterial soft rot pathogen, Pectobacterium carotovorum by Bacillus velezensis CE 100 in cucumber

Pectobacterium carotovorum is a problematic bacterial pathogen causing soft rot in different vegetable crops, resulting in yield losses during pre- and post-harvest periods. In this study, Bacillus velezensis CE 100 showed antibacterial activity against P. carotovorum. Co-inoculation experiment indicated that B. velezensis CE 100 reduced the proliferation rate of P. carotovorum at the early incubation period and that a long incubation time induced a loss of viability of the bacterial pathogen. Agar well diffusion assay revealed that the culture filtrate of strain CE 100 affected the growth of P. carotovorum in a dose-dependent pattern. In time-kill assay, inoculation of P. carotovorum with 50% culture filtrate of strain CE 100 resulted in a complete loss of survival at 4 h incubation period. An antibacterial compound isolated from chloroform extract of B. velezensis CE 100 was identified as macrolactin A based on results of ¹H and ¹³C NMR and mass spectrometry. However, time-kill assay showed that purified macrolactin A at a concentration of 200 μgmL^-1 was not highly effective to control the growth of P. carotovorum although reduction in cell number of P. carotovorum was observed. Moreover, in vivo assay revealed that B. velezensis CE 100 effectively controlled bacterial soft rot. As a consequence, it significantly improved cucumber growth. Therefore, B. velezensis CE 100 could be used as an eco-friendly bioagent for effective control of bacterial soft rot to minimize global economic losses in crop production.