Northern Crop Science Laboratory, USDA-Agricultural Research Service, Fargo, ND 58102-2765, USA.
Pest Manag Sci. 2013 Jan;69(1):35-9. doi: 10.1002/ps.3358. Epub 2012 Jul 3.
Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola, is the most serious foliar disease of sugar beet (Beta vulgaris L.) worldwide. Disease control is mainly achieved by timely fungicide applications. In 2011, CLS control failures were reported in spite of application of quinone outside inhibitor (QoI) fungicide in several counties in Michigan, United States. The purpose of this study was to confirm the resistant phenotype and identify the molecular basis for QoI resistance of Michigan C. beticola isolates.
Isolates collected in Michigan in 1998 and 1999 that had no previous exposure to the QoI fungicides trifloxystrobin or pyraclostrobin exhibited QoI EC(50) values of ≤ 0.006 µg mL(-1) . In contrast, all isolates obtained in 2011 exhibited EC(50) values of > 0.92 µg mL(-1) to both fungicides and harbored a mutation in cytochrome b (cytb) that led to an amino acid exchange from glycine to alanine at position 143 (G143A) compared with baseline QoI-sensitive isolates. Microsatellite analysis of the isolates suggested that QoI resistance emerged independently in multiple genotypic backgrounds at multiple locations. A real-time PCR assay utilizing dual-labeled fluorogenic probes was developed to detect and differentiate QoI-resistant isolates harboring the G143A mutation from sensitive isolates.
The G143A mutation in cytb is associated with QoI resistance in C. beticola. Accurate monitoring of this mutation will be essential for fungicide resistance management in this pathosystem.
由链格孢菌（Cercospora beticola）引起的褐斑病是全世界甜菜（Beta vulgaris L.）最严重的叶部病害。该病的防治主要通过及时施药杀菌剂来实现。然而，2011 年在美国密歇根州的几个县，尽管使用了醌外抑制剂（QoI）杀菌剂，褐斑病的防治仍然失败。本研究的目的是确认密歇根州 C. beticola 分离物对 QoI 的抗性表型，并确定其对 QoI 产生抗性的分子基础。
1998 年和 1999 年在密歇根州采集的、此前未接触过 QoI 杀菌剂三氟醚菌唑或吡唑醚菌酯的分离物，其 QoI 的 EC50 值均≤0.006µg mL(-1)。相比之下，2011 年获得的所有分离物对这两种杀菌剂的 EC50 值均>0.92µg mL(-1)，并且在细胞色素 b（cytb）中存在一个突变，导致第 143 位的甘氨酸突变为丙氨酸（G143A），与基线敏感分离物相比。对分离物的微卫星分析表明，在多个地点的多个基因型背景中，QoI 抗性是独立出现的。开发了一种利用双标记荧光探针的实时 PCR 检测方法，用于检测和区分携带 G143A 突变的 QoI 抗性分离物和敏感分离物。
cytb 中的 G143A 突变与 C. beticola 对 QoI 的抗性有关。该突变的准确监测对于该病害系统中杀菌剂抗性管理至关重要。
