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Effect of essential oils from different accessions of Lippia gracilis on control of Thielaviopsis paradoxa

Costa-Carvalho, R. R., Fontes, M. G., Araujo, E. R., Coelho, I. L., Filho Carvalho, J. L. S., Laranjeira, D., Blank, A. F., Cruz, E. M., Alves, P. B.
Acta horticulturae 2018 no.1198 pp. 27-30
Ceratocystis paradoxa, Lippia, chemotypes, coconuts, control methods, crops, environmental impact, essential oils, fungi, gas chromatography, germplasm, growth retardation, hemorrhage, medicinal plants, mycelium, oils, pathogens, quantitative analysis, Brazil
The coconut can be infected by several pathogens that cause many diseases. However, the stem bleeding caused by the fungus Thielaviopsis paradoxa is the main problem in coconut crops. Alternative control methods can be used in an integrated manner to reduce the environmental impact of chemicals. The use of essential oils obtained from medicinal plants has shown to be of great potential to control pathogens. Thus, the present study had the objective to evaluate the percentage of growth inhibition of T. paradoxa under different concentrations of the essential oil of three Lippia gracilis accessions (L.1, L.2, L.3). The essential oil was extracted from three L. gracilis accessions obtained from the Active Germplasm Bank of the Federal University of Sergipe (UFS). Qualitative and quantitative analyses of the oils were performed in a system of gas chromatography and FID/MS. Concentrations used were 0.1, 0.3, 0.5 and 0.7 µL mL-1. The essential oil was added to the PDA, and then poured into Petri dishes. Each plate was inoculated with mycelium of a disc of 5 mm diameter. The evaluations were performed daily by measuring the diameter of the colonies. All three accessions efficiently controlled the pathogen concentration of 0.3 µL mL-1, and the concentration of 0.1 µL mL-1 was responsible for a control of 20, 80.9 and 60.9% mycelial growth in accession L.1, L.2, L.3, respectively. These results confirm the presence of chemotypes in the specie L. gracilis, since the percentage inhibition of mycelial growth differed significantly among the various accessions at the lowest concentration.