玉米根瘤菌最近被确定为内布拉斯加州玉米和大豆田中的主要根瘤菌,并被证明对玉米和大豆幼苗具有致病性。通常用于控制幼苗疾病的杀菌剂种子处理包括丙硫菌唑(去甲基化抑制剂),氟二恶英(苯基吡咯),sedaxane(琥珀酸脱氢酶抑制剂),和偶氮酯(醌外抑制剂;QoI)。为了确定玉米菌对这些杀菌剂的敏感性,我们在2015年至2017年期间从内布拉斯加州的玉米和大豆田中分离出了这种病原体,并估计了来自内布拉斯加州和伊利诺伊州的91株玉米re分离株中50%抑制的相对有效浓度(EC50)。丙硫菌唑的平均EC50,氟二恶英,sedaxane,和唑菌酯分别为0.219、0.099、0.078和>100µgml-1。在植物中的实验表明,在大豆上没有显着降低疾病的严重程度(P>0.05)。玉米R.的细胞色素b基因没有任何已知赋予QoI抗性的突变,并且在密码子143后直接具有I型内含子,表明G143A突变不太可能在该病原体中进化。对于丙硫菌唑,氟二恶英,和sedaxane,分离株的EC50在收集年份之间没有显着差异(P>0.05),它们的单一区分浓度被鉴定为0.1µgml-1。这是第一个在内布拉斯加州建立玉米R.对唑菌酯的非靶位点抗性以及玉米R.对常用种子处理杀菌剂的敏感性的研究。这些信息将有助于指导玉米r的化学控制策略,并监测未来的敏感性变化。
Rhizoctonia zeae was recently identified as the major Rhizoctonia species in corn and soybean fields in Nebraska and was shown to be pathogenic on corn and soybean seedlings. Fungicide seed treatments commonly used to manage seedling diseases include prothioconazole (demethylation inhibitor), fludioxonil (phenylpyrrole), sedaxane (succinate dehydrogenase inhibitor), and
azoxystrobin (quinone outside inhibitor; QoI). To establish the sensitivity of R. zeae to these fungicides, we isolated this pathogen from corn and soybean fields in Nebraska during 2015 to 2017 and estimated the relative effective concentration for 50% inhibition (EC50) of a total of 91 R. zeae isolates from Nebraska and Illinois. Average EC50 for prothioconazole, fludioxonil, sedaxane, and
azoxystrobin was 0.219, 0.099, 0.078, and > 100 µgml-1, respectively. In planta assays showed that
azoxystrobin did not significantly reduce the disease severity on soybean (P > 0.05). The cytochrome b gene of R. zeae did not harbor any mutation known to confer QoI resistance and had a type-I intron directly after codon 143 suggesting that a G143A mutation is unlikely to evolve in this pathogen. For prothioconazole, fludioxonil, and sedaxane, EC50 of isolates did not differ significantly among years of collection (P > 0.05) and their single discriminatory concentrations were identified as 0.1 µgml-1. This is the first study to establish non-target site resistance of R. zeae to
azoxystrobin and the sensitivity of R. zeae to commonly used seed treatment fungicides in Nebraska. This information will help to guide strategies for chemical control of R. zeae and monitor sensitivity shifts in future.