Antibacterial Activity of Mexican Oregano Essential Oil (Lippia berlandieri) against the Phytopathogenic Bacterium Xanthomonas euvesicatoria

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Xanthomonas euvesicatoria causes bacterial spot disease in leaves, roots, fruits and stems of pepper plants. Identification of this phytopathogen in jalapeno seeds from Delicias, Chihuahua, Mexico and diseased plants from New Mexico, USA, was carried out by isolation on semiselective media,
pathogenicity assays and biochemical tests. Mexican oregano (Lippia berlandieri) essential oil was tested in vitro against Xanthomonas euvesicatoria. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were performed and the oil showed an inhibition of bacterial growth in concentrations of 0.01 mg/ml and a bactericidal effect in concentrations of 0.05 mg/ml. Oregano essential oil is reported
to have antimicrobial activities due to the effect of high content of carvacrol. Oregano oil had an MIC that was 10 times lower compared to pure carvacrol, since carvacrol content, measured by gas chromatography/mass spectrometry (GC/MS) was only 30%. The antimicrobial effect in vivo was tested using a randomized complete block design model in a greenhouse. Disease severity, xanthomonad incidence as well as chlorophyll indices were calculated showing a strong inhibition of the disease, when seeds or foliage were treated with oregano oil. These results demonstrate the current
commonality of xanthomonad pathogens on both sides of the Mexican-American border, and that oregano oil has potent antibacterial activity.

Alba Chavez-Dozal
Hugo A Morales-Morales
Soum Sanogo
Armando Segovia-Lerma
Geoffrey B. Smith
Medio Ambiente y Desarrollo Sustentable