Ajayi-Oyetunde Olutoyosi O, Butts-Wilmsmeyer Carolyn J, Bradley Carl A
Department of Crop Sciences, University of Illinois, Urbana 61801.
Plant Dis. 2017 Mar;101(3):487-495. doi: 10.1094/PDIS-07-16-1015-RE. Epub 2016 Dec 21.
Soybean seedling diseases are caused by Rhizoctonia solani and can be managed with seed-applied fungicides that belong to different chemistry classes. To provide a benchmark for assessing a decline in sensitivities to these fungicide classes, R. solani isolates collected prior to 2001 were evaluated for their sensitivities to succinate dehydrogenase inhibitor (SDHI) (penflufen and sedaxane) and demethylation inhibitor (DMI) fungicides (ipconazole and prothioconazole). The effective concentration of each fungicide that reduced mycelial growth by 50% (EC) was determined in vitro and compared with those of isolates recovered after 2011 from soybean plants with damping off and hypocotyl and root rot symptoms across different soybean-growing regions in the United States and Canada. All isolates, regardless of collection date, were extremely sensitive (EC < 1 μg/ml) to the SDHI fungicides but were either extremely sensitive or moderately sensitive (1 ≤ EC ≤ 10 μg/ml) to the DMI fungicides. For all four active ingredients, variation in sensitivities was observed within and among the different anastomosis groups composing both isolate groups. Isolates collected after 2011, which also had varying in vitro sensitivities, were further evaluated for in vivo sensitivity to the four fungicides in the greenhouse. In vitro fungicide sensitivity did not always coincide with fungicide efficacy in vivo because all isolates tested, regardless of in vitro sensitivity, were effectively controlled by the application of the seed treatment fungicides in the greenhouse. Overall, our results indicate no shift in sensitivity to the fungicide classes evaluated, although considerable variability in the sensitivities of the two groups of isolates examined was present. Based on this research, continued monitoring of fungicide sensitivities of R. solani populations should occur to determine whether sensitivities become further reduced in the future.
大豆幼苗病害由立枯丝核菌引起，可用属于不同化学类别的种衣剂杀菌剂进行防治。为了提供一个评估对这些杀菌剂类别敏感性下降的基准，对2001年之前收集的立枯丝核菌分离株进行了对琥珀酸脱氢酶抑制剂（SDHI）（戊苯吡菌胺和噻唑锌）和脱甲基抑制剂（DMI）杀菌剂（抑霉唑和丙硫菌唑）的敏感性评估。在体外测定了每种使菌丝体生长减少50%的杀菌剂的有效浓度（EC），并与2011年后从美国和加拿大不同大豆种植区出现猝倒、下胚轴和根腐症状的大豆植株中分离得到的分离株的EC进行了比较。所有分离株，无论收集日期如何，对SDHI杀菌剂都极其敏感（EC < 1 μg/ml），但对DMI杀菌剂要么极其敏感，要么中度敏感（1 ≤ EC ≤ 10 μg/ml）。对于所有四种活性成分，在组成两个分离株组的不同融合群内部和之间都观察到了敏感性差异。2011年后收集的分离株在体外敏感性也各不相同，进一步在温室中评估了它们对这四种杀菌剂的体内敏感性。体外杀菌剂敏感性并不总是与体内杀菌剂效力一致，因为所有测试的分离株，无论体外敏感性如何，在温室中通过种子处理杀菌剂的施用都得到了有效控制。总体而言，我们的结果表明，尽管所检测的两组分离株的敏感性存在相当大的变异性，但对所评估的杀菌剂类别没有敏感性变化。基于这项研究，应该持续监测立枯丝核菌群体的杀菌剂敏感性，以确定未来敏感性是否会进一步降低。
