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Antimicrobial activity of Lippia gracilis essential oils on the plant pathogen Xanthomonas campestris pv. campestris and their effect on membrane integrity

da Silva, Rafael Salomão, de Oliveira, Mayara Mendes Gonçalves, de Melo, Juliana Oliveira, Blank, Arie Fitzgerald, Corrêa, Cristiane Bani, Scher, Ricardo, Fernandes, Roberta Pereira Miranda
Pesticide biochemistry and physiology 2019 v.160 pp. 40-48
Brassicaceae, Lippia, Xanthomonas campestris pv. campestris, antimicrobial properties, bacterial growth, biological control, carvacrol, cell membranes, cell viability, chemical analysis, chemical composition, disease control, essential oils, fluorescence, genotype, plant damage, plant pathogens, thymol
Xanthomonas campestris pv.campestris (Xcc) is the causative agent of black rot, a disease that causes serious damage to plants from Brassicaceae family. However, there are no chemicals or biological agent commercially registered for the control of this disease. Thus, this study aimed to evaluate the antimicrobial activity and chemical composition of Lippia gracilis essential oils (EOs) on Xcc aiming its use as effective biological control. We also investigated the effect of EOs on the integrity of the bacterial cytoplasmic membrane. Chemical analysis by GC/MS showed that the major compounds of the seven EOs of L. gracilis are thymol or carvacrol. The seven genotypes showed inhibition of bacterial growth with MIC from 700 μ−1 to 1000 μ−1, with the genotype LGRA-106 (rich in Thymol) with higher antimicrobial activity. The MIC for thymol and carvacrol were 250 μ−1. After exposure to LGRA-106 EO (2×, 1×, 1/2×, 1/4×, and 1/8 x MIC for 5 min, it was observed a decreased cell viability and increased pI fluorescence, which indicates damage to the cytoplasmic cell membrane. This study demonstrates that L. gracilis EOs have antimicrobial activity and have a potential to be used in the control of black rot. Furthermore this antimicrobial activity is due, at least in part, to bacterial cytoplasmic membrane damage.