‘Candidatus Phytoplasma ulmi’ is the agent associated with elm yellows and has been categorised in the European Union as a quarantine pathogen. For central and northern European countries, information on the occurrence and distribution of the pathogen and its impact on elms is scarce, so a survey of native elm trees has been conducted in Germany. About 6500 samples from Ulmus minor, Ulmus laevis and Ulmus glabra, were collected nationwide. Phytoplasma detection was performed by applying a universal 16Sr DNA-based quantitative PCR (qPCR) assay and a novel ‘Ca. P. ulmi’ specific qPCR assay targeting the 16S–23S spacer region. Both assays revealed that 28% of the samples were infected by ‘Ca. P. ulmi’, but infection rates of the elm species and regional incidences differed. The phytoplasma presence in the trees was not correlated to disease-specific symptoms. The survey identified a regional disparity of infection which was high in east, south and central Germany, whereas only a few infected sites were found in the western and northern parts of the country. Monitoring the seasonal titre of ‘Ca. P. ulmi’ in an infected tree by qPCR revealed a high colonisation in all parts of the tree throughout the year. ‘Ca. P. ulmi’ is widely present in elms in Germany. The rare occurrence of symptoms indicates either a high degree of tolerance in elm populations or a low virulence of pathogen strains enabling high infection rates in a long-living host.

中文翻译：

---

在德国，榆树中的“ Candidatus Phytoplasma ulmi”广泛出现。

“ Culidaplasma ulmi”是与榆木黄有关的病原，在欧盟被归类为检疫病原体。对于中欧和北欧国家，有关病原体的发生和分布及其对榆树的影响的信息很少，因此在德国已对原生榆树进行了调查。在全国范围内收集了约6500个小榆，榆和榆的样品。通过应用通用的基于16Sr DNA的定量PCR（qPCR）分析和新颖的'Ca，进行质体检测。P. ulmi针对16S–23S间隔区的特异性qPCR分析。两种测定均显示28％的样品被'Ca感染。P. ulmi'，但榆树物种的感染率和区域发生率有所不同。树木中的植原体存在与疾病特异性症状无关。该调查确定了德国东部，南部和中部地区的感染差异很大，而在该国的西部和北部仅发现了少数感染部位。监测'Ca的季节性滴度。通过qPCR在被感染树中的P. ulmi'揭示了全年树的所有部位都有很高的定殖率。'Ca。P. ulmi'在德国的榆树中广泛存在。罕见的症状表明，榆树种群具有高度的耐受性，或者病原体菌株的毒力低，使得长寿宿主的感染率很高。而在该国的西部和北部仅发现了少数感染点。监测'Ca的季节性滴度。通过qPCR在被感染树中的P. ulmi'揭示了全年树的所有部位都有很高的定殖率。'Ca。P. ulmi'在德国的榆树中广泛存在。罕见的症状表明，榆树种群具有高度的耐受性，或者病原体菌株的毒力低，使得长寿宿主的感染率很高。而在该国的西部和北部仅发现了少数感染点。监测'Ca的季节性滴度。通过qPCR在被感染树中的P. ulmi'揭示了全年树的所有部位都有很高的定殖率。'Ca。P. ulmi'在德国的榆树中广泛存在。罕见的症状表明，榆树种群具有高度的耐受性，或者病原体菌株的毒力低，使得长寿宿主的感染率很高。