Atividade antifúngica "in vitro" de óleos essenciais e produtos químicos sobre Alternaria alternata

Abstract

Alternaria spot is caused by the fungus Alternaria alternata (PERES et al., 2003) and has been reported in several plant species, causing dark necrotic lesions that occur mainly on the leaves, stems and fruits of plants. Among the disease control measures, the main one is the use of fungicides in seed treatment or plant protection. However, modern agriculture aimed at obtaining quality plant products, free from contamination by microorganisms and chemical residues, requires alternative methods to pesticides, such as the use of essential oils. Therefore, this work aimed to evaluate the in vitro antifungal effect of chemicals recommended for the treatment of seeds and essential oils at different concentrations on the mycelial growth of Alternaria alternata. The experiment consisted of two in vitro assays, which were carried out at the Phytopathology Laboratory of the Agronomy Course Campus at the Federal University of Santa Maria in Frederico Westphalen. The fungus A. alternata was obtained from the fungus collection of the Laboratory of Phytopathology, being the same isolated from bean seeds (Phaseolus vulgaris). In test 1, the sensitivity of the fungus A. alternata to the chemical products CARBENDAZIM NORTOX® (CARBENDAZIM 500g/l) and DEROSAL PLUS® (CARBENDAZIM 150g/l + Tiram 350g/l), at concentrations of 0, 1, 10, 100 and 1000 ppm. And in test 2, the fungitoxic effect of the essential oils of EUCALYPTUS and CITRONELA, obtained commercially, at concentrations of 0, 100, 250, 500 and 1000 ppm on A. alternata was determined. The parameters for evaluating the antifungal activity of chemicals and essential oils, for the two assays, were final colony diameter (DFC), mycelial growth rate index (IVCM) and percentage of inhibition of colony growth (PIC). For the fungicides tested, DEROSAL PLUS® showed the best in vitro control over the fungus A. alternata. The essential oils tested showed antifungal activity against A. alternata, however the greatest inhibitions were provided by CITRONELA oil with 67%, at the highest concentrations. Although in individual tests it is possible to verify that the tested essential oils provided a percentage of inhibition of mycelial growth superior to the tested chemical products, demonstrating a viable option in the alternative control of this pathogen.