Sensibilidade de isolados de Alternaria brassicicola a ditiocarbamato, estrobilurina e triazol

Abstract

Alternaria leaf spot is one of the predominant diseases in brassica crops, caused by several species of Alternaria, with A. brassicicola being the species present in cabbage crops in Brazil. The present work aimed to evaluate the in vitro and in vivo sensitivity of A. brassicicola to dithiocarbamate (mancozeb), strobilurin (azoxystrobin) and triazole (difeconazole), as well as their adaptability components. A total of thirty A. brassicicola isolates from producing areas in Brazil were used to obtain in vitro sensitivity. The in vitro sensitivity of the isolates was evaluated by estimating the concentration capable of inhibiting 50% of mycelial growth (EC50). Six isolates were classified as sensitive with EC50 ranging from 153.5 to 383.3 μg.mL-1 for mancozeb, from 6.5 to 9.4 μg.mL-1 for azoxystrobin and from 3.6 to 5.0 μg.mL-1 for difeconazole, and six isolates in non-susceptible strains with EC50 for mancozeb above 500 μg.mL-1, for azoxystrobin >10.2 μg.mL-1 and difeconazole >5.1 μg.mL-1. Twelve isolates were used in the in vivo susceptibility assays, and the lesion diameter of cabbage plants was evaluated using commercial doses of mancozeb, azoxystrobin and difeconazole. The twelve isolates selected in the in vitro test in sensitive and non-sensitive were compared in terms of mycelial growth, conidia production, conidia germination and virulence. Most isolates tested in vitro were sensitive to fungicides. All plants not treated with fungicides and inoculated with susceptible isolates showed typical symptoms of Alternariose. The percentage of inhibition of mycelial growth varied between sensitive and non-sensitive isolates of A. brassicicola. There is a difference between fungicides, such as difeconazole, which showed 80.85% inhibition of lesion diameter for sensitive isolates and 87.14% for non-sensitive isolates. There was a statistical difference in the mycelial growth rate for the active ingredient mancozeb, in the production of conidia and virulence for azoxystrobin. The results indicate the presence of sensitive and non-sensitive individuals in producing areas, with good adaptability characteristics, showing the need to adopt more efficient and strategic control measures for monitoring non-sensitive populations.