In vivo sensitivity of Phakopsora pachyrhizi to DMI and QoI fungicides

In in vivoexperiments the sensitivity of 18 isolates of Phakopsora pachyrhizifrom several regions of Brazil to IDM fungicides (cyproconazole, epoxiconazole and tebuconazole and an IQE (pyraclostrobin) were evaluated. The assessments were based on leaflet uredia density. Inhibitory concentration (IC50) and sensitivity reduction factor were determined for all fungicide x strain interactions. Tebuconazole sensitivity reduction was detected for most fungus isolates. In contrast, there was no fungicide shift in sensitivity of the fungus to pyraclostrobin. We conclude that the control failure of soybean rust found in some farms is due to the reduced sensitivity of the fungus to the IDM fungicide and that it remains sensitive to pyraclostrobin.

本研究通过体内试验，评估了采自巴西多个地区的18株大豆锈菌（Phakopsora pachyrhizis）对脱甲基化抑制剂类杀菌剂（IDM fungicides，包括环丙唑醇、环氧菌唑与戊唑醇）以及1种喹啉氧化酶抑制剂（IQE，即吡唑醚菌酯pyraclostrobin）的敏感性。试验评估以小叶夏孢子堆密度为指标。针对所有杀菌剂-菌株互作组合，本研究测定了半最大抑制浓度（IC50）与敏感性降低因子。结果显示，多数菌株对戊唑醇的敏感性出现下降；与之相反，该病原菌对吡唑醚菌酯的敏感性未发生显著变化。本研究得出结论：部分农场出现的大豆锈病防治失效问题，源于该病原菌对脱甲基化抑制剂类杀菌剂的敏感性降低，且其对吡唑醚菌酯仍保持敏感。