Fungitoxicidade de óleos essenciais sobre Colletotrichum theobromicola, cau-sador da antracnose da cebolinha (Allium fistulosum L.).

Abstract

Fungitoxicity of essential oils on Colletotrichum theobromicola, causing an-thracnose of Allium fistulosum L. ABSTRACT: Essential oils are promising alternatives for the management of plant diseases due to their recognized antimicrobial activity. The objective of this research was to evaluate the fungitoxic effect of essential oils of some species of the genus Piper spp., and Lippia spp., in the alternative control to Colletotrichum theobromicola causal agent of the anthracnose of Al-lium fistulosum. The essential oils were obtained by hydrodistillation and the chemical compo-sition of the oils was determined by GC-MS. The in vitro evaluation was carried out in three stages: I - effect of essential oils on mycelial growth, II - action of oils on conidial germination and III - effect of essential oils on the morphology of C. theobromicola hyphae. The experi-ments were conducted in a completely randomized design in a 5 x 5 (five Piper spp.) and 3 x 5 (Lippia spp) with five concentrations (0, 0.1, 0.2, 0.5, 1%). In the in vivo experiment, 1% of the respective essential oils were applied in a preventive manner directly to the A. fistulosum inoculated with C. theobromicola and thus evaluated the incidence and severity of anthracnose. The experiment was also conducted in a randomized design with five replicates. The experi-ment was also conducted in a randomized design with five replicates. All data were submitted to analysis of variance and the averages were the averages of Tukey's test at 0.05. The results of the major components of the essential oils showed that these natural products have several different chemical substances in their composition. For P. aduncum L. the major component detected by CG-MS was apiol (93.83%); P. hispidinervum and P. callosum safrole (79.96%) and (83.61%); P. hispidum or m-micene (56.53%); P. marginatum or Bicyclo [4.1.0] hept-3-ene, 3,7,7-trimethyl (41,23%); L. alba or carvone (96.2%); L. gracilis and carvacrol (84.98%) and L. sidoides and o-cymene (29.99%), respectively. It was found that essential oils of all species and in all studied concentrations inhibited the growth of C. theobromicola. The species P. callosum, P. hispidinervum, P. marginatum, L. alba (1) and L. gracilis provided reduction of the colony diameter at 0.90 cm and inhibited the mycelial growth of the fungus at 0, 2%. In relation to the percentage of inhibition of conidial germination to P. callosum and L. alba (1), the best results were obtained, since from the lowest concentration (0.1%) there was 100% inhibition of spore germination. Observations in scanning microscopy, hypothetical C. theo-bromicola hyphae exposed to the concentration 1% showed changes in their morphology, being degraded and wrinkled. In relation to the effect of essential oils on the incidence of anthracnose, the best results were obtained with the essential oils of P. aduncum, followed by P. marginatum and L. alba (1) in which it reduced 10, 30 and 45% of the disease in field. This research confirms the efficacy of the essential oils of some species of the genus Piper and Lippia both in vitro and in vivo and emphasizes the importance of these products in phytopathogenic control. Given the results obtained, the research provides a basis for further studies in this regard. Keywords: Piper spp., Lippia spp., Alternative control, natural products.