Atividade antimicrobiana e antibiofilme de óleos essenciais de Lippia gracilis e seus compostos majoritários sobre fitopatógenos do gênero Xanthomonas spp. resistentes ao cobre

Abstract

The genus Xanthomonas is formed by gram-negative phytobacteria that produce biofilms and that cause diseases in plants of economic importance. Prominent diseases include black rot of crucifers, water belly of melon, gummosis of sugar cane, bacterial leaf streak of corn, and bacterioses of cassava and plum. Due to the need for new alternatives for treatment of these diseases, essential oils (EOs) have been studied, which are plant secondary metabolites that have different biological activities, such as antibacterial activity. The objective of this study was to evaluate the antimicrobial and antibiofilm activity of EOs from seven accessions of Lippia gracilis Schauer (LGRA-106, 107, 108, 109, 110, 201, and 202) obtained through the hydrodistillation technique and their major compounds thymol and carvacrol, as well as evaluate copper resistance in five species of phytobacteria of the genus Xanthomonas: Xanthomonas campestris pv. melonis, Xanthomonas axonopodis pv. manihotis, Xanthomonas campestris pv. pruni, Xanthomonas axonopodis pv. vasculorum, and Xanthomonas campestris pv. campestris. Using spectrophotometric techniques, Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC), antibiofilm activity, cell viability, plasma membrane permeabilization, and resistance to sulfate and copper oxide were evaluated; and the biofilm was morphologically examined under microscopy in vitro. scanning electronics. The in vivo study was carried out in an agricultural greenhouse. The effect of the EO from the LGRA107 accession (previously selected for its greater bacteriostatic and bactericidal activity against X. campestris pv. campestris) and the effect of copper oxide were examined on two varieties of kale plants (Georgia and Ramoso Santana) inoculated with Xanthomonas campestris pv. campestris regarding the following variables: number of leaves, biomass, and incidence and severity of disease. The in vitro experiments were performed in duplicate with three replications. For the in vivo experiment, a completely randomized design was used in a 2 × 3 factorial arrangement, constituted by two inoculation methods (injected and sprayed) and three substances (two concentrations of EO from the LGRA-107 accession – 250 and 500 µg mL-1 , and a copper oxide concentration – 2000 µg mL-1 ). A control of 1% DMSO was also used. For analysis of disease severity and incidence, a scoring scale from 0 to 5 was used, and evaluations were carried out over a period of 15 days. The concentration of 1000 µg mL-1 of EOs from LGRA accessions and the major compounds thymol and carvacrol at concentrations between 250 and 500 µg.mL-1 , respectively, demonstrated bacteriostatic and bactericidal activity and led to an increase in cell plasma membrane permeability bacterial. The EOs of all accessions, as well as the major compounds and copper oxide, showed antibiofilm activity for the five phytobacteria. However, this activity was not observed for copper sulfate. As the result of the in vivo experiment, kale, when exposed to copper oxide, obtained higher values of fresh biomass, and broccoli kale had higher leaf numbers. The results of this study showed that the essential oils of the accessions LGRA-109, LGRA-201, and LGRA-107 had greater antimicrobial activity and are promising for control of phytobacteria of the genus Xanthomonas spp.