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The essential oil of Plectranthus amboinicus and its chemotypes, carvacrol and thymol, were evaluated on the germination and root and aerial growth of Lactuca sativa and Sorghum bicolor and in acting on the cell cycle of meristematic root cells of L. sativa. The main component found in the oil by analysis in gas chromatography-mass spectrometry and gas chromatography flame ionization detection was carvacrol (88.61% in area). At a concentration of 0.120% (w v(-1)), the oil and its chemotypes retarded or inhibited the germination and decreased root and aerial growth in monocot and dicot species used in the bioassays. In addition, all substances caused changes in the cell cycle of the meristematic cells of L. sativa, with chromosomal alterations occurring from the 0.015% (w v(-1)) concentration. The essential oil of P. amboinicus, carvacrol, and thymol have potential for use as bioherbicides.

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Semisynthetic phenol derivatives were obtained from the natural phenols: thymol, carvacrol, eugenol, and guaiacol through catalytic oxychlorination, Williamson synthesis, and aromatic Claisen rearrangement. The compounds characterization was carried out by H NMR,C NMR, and mass spectrometry. The natural phenols and their semisynthetic derivatives were tested for their antimicrobial activity against the bacteria: Staphylococcus aureus, Escherichia coli, Listeria innocua, Pseudomonas aeruginosa, Salmonella enterica Typhimurium, Salmonella enterica ssp. enterica, and Bacillus cereus. Minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values were determined using concentrations from 220 to 3.44 μg mL. Most of the tested compounds presented MIC values ≤220 μg mL for all the bacteria used in the assays. The molecular properties of the compounds were computed with the PM6 method. Through principle components analysis, the natural phenols and their semisynthetic derivatives with higher antimicrobial potential were grouped.

The thrips, Frankliniella schultzei, and green peach aphid, Myzus persicae, cause direct damage to plants of economic importance and transmit phytoviruses, causing large economic losses. Chemical constituents of essential oils present a wide range of biological activities. The aim of this work was to evaluate insecticidal activity of essential oil from citronella grass, Cymbopogon winterianus, on F. schultzei and M. persicae. This essential oil was obtained by steam distillation and components were identified by GC/FID and GC/MS. A Potter spray tower was used to spray insects with the essential oil. The major constituents are geraniol (28.62%), citronellal (23.62%) and citronellol (17.10%). Essential oil of C. winterianus at 1% (w v -1 ) causes mortality in F. schultzei and M. persicae at 34.3% and 96.9%, respectively. The LC 50 value for M. persicae was 0.36% and LC 90 0.66%. Thus, citronella grass essential oil at 1% (w v -1 ) is more toxic to M. persicae than F. schultzei. This essential oil shows promise for developing pesticides to manage M. persicae. Index terms:Cymbopogon winterianus, thrips, green peach aphid, volatile components, natural insecticide. RESUMOO tripes, Frankliniella schultzei, e o pulgão-verde, Myzus persicae, além de causarem danos diretos a plantas de importância econômica, também são importantes transmissores de fitoviroses, acarretando grandes perdas econômicas. Os constituintes químicos dos óleos essenciais têm sido cada vez mais estudados, pois apresentam uma ampla gama de atividades biológicas. Neste trabalho, objetivou-se avaliar a atividade inseticida do óleo essencial de capim-citronela, Cymbopogon winterianus, sobre F. schultzei e M. persicae. O óleo essencial foi obtido por hidrodestilação e a identificação dos seus componentes foi realizada por CG/DIC e CG/EM. Uma torre de Potter foi utilizada para pulverizar os insetos com óleo essencial. Os componentes majoritários encontrados são geraniol (28,62%), citronelal (23,62%) e citronelol (17,10% ) é mais tóxico para M. persicae do que para F. schultzei. Este óleo essencial mostra-se promissor para o desenvolvimento de inseticidas para o manejo de M. persicae. Termos para indexação:Cymbopogon winterianus, tripes, pulgão-verde, componentes voláteis, inseticida natural.

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