Department of Plant Pathology, University of Kentucky.
Science, Technology, Engineering, Arts, and Mathematics Academy, Lexington, KY, U.S.A.
Plant Dis. 2020 Jun;104(6):1781-1788. doi: 10.1094/PDIS-02-19-0382-RE. Epub 2020 Apr 13.
Azoxystrobin is the only synthetic, systemic fungicide labeled in the United States for management of frogeye leaf spot (FLS) of tobacco ( L.), caused by . Though traditionally considered a minor disease in the United States, FLS has recently become yield and quality limiting. In 2016 and 2017, 100 isolates were collected from symptomatic tobacco from eight counties in Kentucky, United States. Prior to azoxystrobin sensitivity testing, some isolates were found to utilize the alternative oxidase pathway and, after assay comparisons, conidial germination was utilized to evaluate sensitivity in as opposed to mycelial growth. Azoxystrobin sensitivity was determined by establishing the effective concentration to inhibit 50% conidial germination (EC) for 47 (in 2016) and 53 (in 2017) isolates. Distributions of EC values indicated three qualitative levels of sensitivity to azoxystrobin. Partial sequence, encompassing the F129L and G143A mutation sites, indicated single-nucleotide polymorphisms (SNPs) conferring the F129L mutation in of moderate resistance (azoxystrobin at 0.177 ≤ EC ≤ 0.535 µg/ml) and the G143A mutation in isolates with an azoxystrobin-resistant phenotype (azoxystrobin EC > 1.15 µg/ml). Higher frequencies of resistant isolates were identified from greenhouse transplant (4 of 17) and conventionally produced (58 of 62) tobacco samples, as compared with field-grown tobacco (<4 weeks prior to harvest; 4 of 62) or organically produced samples (1 of 7), respectively. Together, these results suggest that resistance to azoxystrobin in occurs broadly in Kentucky, and generate new hypotheses about selection pressure affecting resistance mutation frequencies.
咯菌腈是唯一一种在美国被标记用于防治烟草蛙眼病（FLS）的合成、系统性杀菌剂，由 引起。尽管在传统上被认为是美国的一种次要疾病，但 FLS 最近已成为限制产量和质量的因素。2016 年和 2017 年，从美国肯塔基州八个县的有症状烟草中收集了 100 个分离株。在进行咯菌腈敏感性测试之前，发现一些分离株利用备用氧化酶途径，并且在进行了试验比较后，使用分生孢子萌发来评估 中的敏感性，而不是菌丝生长。通过确定抑制 50%分生孢子萌发的有效浓度（EC）来确定咯菌腈敏感性，对 47 个（2016 年）和 53 个（2017 年）分离株进行了测试。EC 值的分布表明对咯菌腈的敏感性存在三种定性水平。包含 F129L 和 G143A 突变位点的部分 序列表明，导致中度抗性（咯菌腈 EC 值为 0.177≤EC≤0.535μg/ml）的 F129L 突变和具有咯菌腈抗性表型的分离株中的 G143A 突变的单核苷酸多态性（SNP）。与田间生长的烟草（收获前<4 周；62 个中的 4 个）或有机生产的样品（分别为 1 个中的 7 个）相比，温室移植（17 个中的 4 个）和常规生产（62 个中的 58 个）烟草样本中鉴定出具有抗性的分离株的频率更高。总的来说，这些结果表明，在肯塔基州， 对咯菌腈的抗性广泛存在，并提出了关于影响抗性突变频率的选择压力的新假设。
