Vaghefi Niloofar, Hay Frank S, Kikkert Julie R, Pethybridge Sarah J
School of Integrative Plant Sciences, Plant Pathology & Plant-Microbe Biology Section, Cornell University, Geneva, NY 14456.
Cornell Cooperative Extension, Canandaigua, NY 14424.
Plant Dis. 2016 Jul;100(7):1466-1473. doi: 10.1094/PDIS-09-15-1014-RE. Epub 2016 Mar 7.
Cercospora leaf spot (CLS), caused by Cercospora beticola, is one of the major diseases affecting productivity and profitability of beet production worldwide. Fungicides are critical for the control of this disease and one of the most commonly used products is the quinone outside inhibitor (QI) azoxystrobin. In total, 150 C. beticola isolates were collected from two commercial processing table beet fields in Batavia, NY in 2014. The mating types of the entire population were determined, and genetic diversity of a subset of samples (n = 48) was assessed using five microsatellite loci. Sensitivity to azoxystrobin was tested using a spore germination assay. The cytochrome b gene was sequenced to check for the presence of point mutations known to confer QI resistance in fungi. High allelic diversity (H = 0.50) and genotypic diversity (D* = 0.96), gametic equilibrium of the microsatellite loci, and equal ratios of mating types were suggestive of a mixed mode of reproduction for C. beticola. Resistance to azoxystrobin was prevalent because 41% of the isolates had values for effective concentrations reducing spore germination by 50% (EC) > 0.2 μg/ml. The G143A mutation, known to cause QI resistance in C. beticola, was found in isolates with EC values between 0.207 and 19.397 μg/ml. A single isolate with an EC of 0.272 μg/ml carried the F129L mutation, known to be associated with low levels of QI resistance in fungi. This is the first report of the F129L mutation in C. beticola. The implications of these findings for the epidemiology and control of CLS in table beet fields in New York are discussed.
由甜菜尾孢菌引起的尾孢叶斑病（CLS）是影响全球甜菜生产产量和利润的主要病害之一。杀菌剂对控制这种病害至关重要，最常用的产品之一是醌外抑制剂（QI）嘧菌酯。2014年，从纽约巴达维亚的两个商业加工食用甜菜田中共收集了150株甜菜尾孢菌分离株。确定了整个群体的交配型，并使用五个微卫星位点评估了一部分样本（n = 48）的遗传多样性。通过孢子萌发试验测试了对嘧菌酯的敏感性。对细胞色素b基因进行测序，以检查是否存在已知会导致真菌产生QI抗性的点突变。高等位基因多样性（H = 0.50）和基因型多样性（D* = 0.96）、微卫星位点的配子平衡以及交配型的等比例表明甜菜尾孢菌具有混合繁殖模式。对嘧菌酯的抗性很普遍，因为41%的分离株的有效浓度（使孢子萌发减少50%的浓度，即EC）值> 0.2 μg/ml。在EC值介于0.207和19.397 μg/ml之间的分离株中发现了已知会导致甜菜尾孢菌产生QI抗性的G143A突变。一株EC为0.272 μg/ml的分离株携带F129L突变，已知该突变与真菌中低水平的QI抗性有关。这是首次在甜菜尾孢菌中报道F129L突变。讨论了这些发现对纽约食用甜菜田CLS流行病学和防治的影响。
