The fungus Corynespora cassiicola causes target spot on soybeans in Brazil and one of the recommended controls for this disease involves the use of fungicides. Here, we evaluated the sensitivity of C. cassiicola isolates to fungicides, comparing the effective concentrations required to inhibit 50% of fungal growth (EC50) using a colorimetric microtiter method, with the EC50 determined by mycelial growth inhibition in a fungicide-amended medium obtained by Xavier et al. (2013), for 16 isolates for carbendazim and prothioconazole. The correlation between EC50 values for both methods were 0.90 and 0.88 for carbendazim and prothioconazole, respectively. After this, the sensitivities of 134 C. cassiicola isolates collected in soybean fields in Paraná (PR) and Mato Grosso (MT) in the 2012/13 and 2013/14 crop seasons to carbendazim, prothioconazole, and pyraclostrobin fungicides were evaluated using microtiter method. The spores of the isolates were diluted in Yeast Bacto Acetate culture medium and added to fungicide solutions at concentrations of zero; 0.0032; 0.016; 0.08; 0.4; 2; 10; and 50 μg mL⁻¹. A microplate reader with a 540 nm wavelength was used to estimate the EC50 values. Isolates showed growth inhibition at concentrations higher than 50 μg mL⁻¹, showing a high frequency of resistant isolates, in total, 67% of the isolates from PR and 88% from MT (carbendazim); 99% from PR and 82% from MT (pyraclostrobin); and 11% from PR and 9% from MT (prothioconazole). The results showed that the lower control efficiency for target spot in soybeans in PR and MT to MBC and QoI fungicides could be associated with the presence of resistant isolates.

真菌Corynespora cassiicola在巴西的大豆上引起目标点，该病的推荐控制措施之一是使用杀真菌剂。在这里，我们评估了C. cassiicola分离株对杀菌剂的敏感性，比较了使用比色微量滴定法抑制50％真菌生长所需的有效浓度（EC50），以及通过在获得杀菌剂改良的培养基中抑制菌丝体生长而确定的EC50。由Xavier等人撰写。（2013年），用于多菌灵和丙硫菌唑的16种分离物。这两种方法的EC50值之间的相关性分别是多菌灵和丙硫康唑分别为0.90和0.88。此后，对134 C. cassiicola的敏感性使用微量滴定法评估了2012/13和2013/14作物季节在巴拉那州（PR）和马托格罗索州（MT）的大豆田中收集的多菌灵，原硫代康唑和吡咯菌酯杀菌剂的分离株。将分离物的孢子在酵母酵母醋酸盐培养基中稀释，并以零浓度加入杀真菌剂溶液中。0.0032; 0.016；0.08；0.4; 2; 10; 和50μgmL ^-1。使用波长为540 nm的酶标仪评估EC50值。分离物在浓度高于50μgmL ^-1时显示出生长抑制，显示抗药性菌株的频率很高，总共有67％的PR菌株和88％的MT（多菌灵）菌株；99％来自PR，82％来自MT（吡咯菌酯）；来自PR的11％和来自MT（原硫代康唑）的9％。结果表明，PR和MT对MBC和QoI杀真菌剂对大豆目标点的控制效率较低可能与抗性菌株的存在有关。