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Effect of essential oils from Lippia sidoides and Lippia gracilis on growth inhibition of Rhizoctonia solani

Silva, V. M., Costa-Carvalho, R. R., Fontes, M. G., Laranjeira, D., Blank, A. F., Alves, P. B.
Acta horticulturae 2018 no.1198 pp. 31-34
Lippia sidoides, Thanatephorus cucumeris, carvacrol, crops, culture media, essential oils, fungi, growth retardation, mycelium, oils, plant pathogens, seeds, soil, steam distillation, thymol
Rhizoctonia solani is a plant pathogen, inhabitants of soil, which causes great losses in many economically important crops. This study aimed to evaluate the effect of essential oils from Lippia sidoides and L. gracilis on in vitro inhibition of mycelial growth of two isolates of R. solani. The essential oils were extracted from leaves of L. sidoides and L. gracilis by steam distillation method. The chemical components of the oils were identified by comparison of mass spectra and comparison of the retention indexes. Concentrations used were 0.02, 0.04, 0.06, 0.08, and 0.1 μL mL-1 of each oil and these were distributed into PDA culture medium. The evaluation was performed daily by measuring the diameter of the colonies. The essential oil from L. sidoides completely inhibited the fungi growth in both isolates of R. solani, in all tested concentrations. The essential oil from L. gracilis inhibited isolate R2 at all tested concentrations, whereas the isolate R1 of the pathogen was completely inhibited from the concentration 0.04 μL mL-1. The inhibition caused by the essential oils from L. sidoides and L. gracilis is probably due to the high content of thymol (42.33 and 18%, respectively) and carvacrol (4.56 and 27.59%, respectively). The result impresses with very low concentration of essential oils required for inhibition of mycelial growth of R. solani and could become a powerful tool in the treatment of seeds.