Abstract

Corynespora cassiicola which cause the target spot in soybeans can lead to significant reductions in grain yield. Chemical control mechanisms recommended for disease control was performed with low efficacy in the field due to loss of the pathogen sensitivity to fungicides. This study evaluated the effect of fungicides in inhibiting C. cassiicola using in vitro test. Four isolates from different regions of Rio Verde - GO were used. The experimental design was completely randomized with nine treatments and five doses (0.0, 0.1, 1.0, 10 and 100 mg). The fungicides, in the various concentrations, were added in PDA medium and poured into Petri dishes, 80 mm in diameter. Then 5 mm discs, containing fungy mycelia, were transferred to the center of the plate and incubated in growth chamber at 25°C with photoperiod of 12 h. The mycelial growth in colony diameter was measured every 24 h. The inhibition percentage of each fungicide on various isolates of fungi was determined, by observing area under the curve of mycelial progress (AUCMP) and by determining the mycelial growth speed rate (MGSR) was determined. All treatments showed a decrease in SRMG with increased applied dose, the fungicide fluazinam had the best performance, with 100%  mycelial growth inhibition at all dose tested and in both areas in which the isolate was obtained. The choice of product and dose to be applied directly will be helpful in the chemical control programs ensuring higher yields at the end of the crop cycle.

Key words: Target spot, Corynespora cassiicola, in vitro, test.