Fungicidas para patógenos necrotróficos do cafeeiro: avaliação da dose resposta ‘in vitro’ e dos efeitos fisiológicos em mudas

Abstract

The objective of the present study is to determine, 'in vitro', the dose-response of fungicides that inhibit demethylation (DMI), quinone oxidase (QoI) and succinate dehydrogenase in inhibiting the mycelial growth of the fungi Cercospora coffeicola, Phoma tarda and Colletotrichum gloeosporioides and evaluate, in a greenhouse, the physiological increase of coffee plants through the application of fungicides. Eight active principles from the group of Strobilurins, Triazoles, Carboxamides and Anilide were evaluated at concentrations equivalent to 5, 25, 50 and 100% of the field dose, in the mycelial inhibition of the fungi under study. The evaluation was carried out by measuring the diameter of the colonies perpendicularly, until the fungus reached the edge of the plate. The mycelial growth velocity index (MGVI) was calculated to obtain the dose response. The physiological effects of fungicides used to control coffee necrotrophic pathogens on seedlings was implanted in a greenhouse. The experimental design was in randomized blocks, consisting of seven treatments, the control, Difenoconazole + Pydiflumetofen, Azoxystrobin + Difenoconazole, Boscalid, Trifloxystrobin + Tebuconazole, Azoxystrobin + Tebuconazole and Pyraclostrobin + Fluxapyroxad and five replications. Height, diameter, leaf area, chlorophyll content, dry weight, total phenols, lignin content and wax layer of the plants were evaluated. For coffee necrotrophic pathogens (C. gloeosporioides, P. tarda and C. coffeicola) the response dose indicated for studies of mycelial growth and MGVI is 5% of the field dose, with Azoxystrobin 11.3 ppm + Tebuconazole 18.8 ppm, Tebuconazole 20 ppm + Trifloxystrobin 10 ppm, Difenoconazole 6.3 ppm + Pydiflumetofen 3.8 ppm, Azoxystrobin 10 ppm + Difenoconazole 6.3 ppm, Boscalid 9.4 ppm and Pyraclostrobin 25 ppm + Fluxapyroxad 12.5 ppm. For C. gloeosporioides Difenoconazole + Pydiflumetofen, Azoxystrobin + Difenoconazole, Tebuconazole + Trifloxystrobin and Azoxystrobin + Tebuconazole obtained IC50 values below 0.1 ppm, for IC90, the lowest values were verified for Azoxystrobin + Tebuconazole and Tebuconazole + Trifloxystrobin. For P. tarda, Difenoconazole + Pydiflumetofen, Azoxystrobin + Difenoconazole, Boscalid and Pyraclostrobin + Fluxapyroxad showed IC50 doses lower than 1 ppm of fungicide and for IC90, Difenoconazole + Pydiflumetofen, Azoxystrobin + Difenoconazole and Pyraclostrobin + Fluxapyroxad showed doses lower than 1 ppm. For C. coffeicola Difenoconazole + Pydiflumetofen, Azoxystrobin + Difenoconazole, Tebuconazole + Trifloxystrobin and Azoxystrobin + Tebuconazole, showed IC50 lower than 1 ppm and for IC90, Azoxystrobin + Difenoconazole and Tebuconazole + Trifloxystrobin showed dose response lower than 1 ppm. There was no difference in height, diameter, aerial part and chlorophyll content in coffee seedlings. The smallest aerial part weight of dry seedlings was found in the Tebuconazole + Trifloxystrobin treatment. Thirty days after spraying, the treatments Azoxystrobin + Tebuconazole, Boscalida and Difenoconazole + Pydiflumetofen showed higher values of total phenols. The Difenoconazole + Pydiflumetofen treatment increased the amount of lignin. In all treatments with fungicides, a wax layer was observed. No symptoms of phytotoxicity were observed.