Sensitivity of populations of Phakopsora pachyrhizi to the fungicide prothioconazole

ABSTRACT Reduced efficiency of synthetic fungicides is associated with the selection of individuals presenting genetic alterations that provide resistance to active ingredients. Signs of variations in the frequency of resistant individuals among fungal populations can be quantified based on the effective concentration 50 (CE50). The objective of this study was to evaluate the sensitivity to prothioconazole (DMI) by populations of Phakopsora pachyrhizi collected during the 2017/18 harvest from different soybean producing regions, based on the effective concentration that results in 50% control efficiency (CE50). Soybean leaflets were treated with a.i. at the concentrations zero; 0.0625; 0.125; 0.25; 0.5; 1; 2; 4; 8 and 16 mg L-1 and inoculated with P. pachyrhizi uredospores from 17 localities distributed in Brazil and Paraguay. The inoculated leaflets were kept in 15cm-diameter plastic Petri dishes containing moistened filter paper and incubated in growth chambers at 23 ± 2°C. The disease severity was evaluated 15 days after inoculation. Log-logistic adjustment was employed to estimate the effective concentration that had 50% control efficiency (CE50) for each population. There was variation in the sensitivity of P. pachyrhizi populations to the fungicide prothioconazole, and CE50 values ranged from 0.05 mg L-1 to 1.04 mg L-1 with mean and median values of 0.35 mg L-1. According to the obtained results, sensitivity of P. pachyrhizi to the fungicide prothioconazole varied with the origin of the fungal populations.

摘要
合成杀菌剂的药效衰减，与携带有可使菌体对有效成分产生抗性的遗传变异的菌株被筛选富集密切相关。真菌种群中抗性菌株频率的变化特征，可通过有效中浓度（CE50）进行量化分析。本研究旨在基于引发50%防控效果的有效中浓度（CE50），评估2017/2018年度收获季从不同大豆产区采集的大豆锈菌（*Phakopsora pachyrhizi*）种群对丙硫菌唑（DMI）的敏感性。
以有效成分（a.i.）浓度分别为0（空白对照）、0.0625、0.125、0.25、0.5、1、2、4、8及16 mg·L⁻¹的药液处理大豆小叶，随后接种采自巴西与巴拉圭境内17个采样点的大豆锈菌夏孢子。将接种后的小叶置于铺有湿润滤纸的15cm直径塑料培养皿中，于23±2℃的生长箱内培养。接种15天后，调查病害严重度。采用双对数Logistic模型拟合，估算各供试种群的50%防控效果有效中浓度（CE50）。
结果表明，不同大豆锈菌种群对丙硫菌唑的敏感性存在显著差异，CE50值范围为0.05 mg·L⁻¹至1.04 mg·L⁻¹，平均值与中位数均为0.35 mg·L⁻¹。综上结果显示，大豆锈菌对丙硫菌唑的敏感性随菌株种群的采集地域不同而存在差异。