The downy mildew pathogen Pseudoperonospora humuli is a major disease of cultivated and wild hop (Humulus lupulus) in many hop-growing areas of the world. Despite its frequent occurence and economic impact, so far very little is known with respect to its population structure, which would be a prerequisite for understanding population dynamics and for successful resistance breeding efforts. We collected a set of 70 P. humuli samples in five European countries (Austria, the Czech Republic, France, Germany, Italy) around the Alps, a high mountain range and a known major hurdle for dispersal, and examined them with microsatellite markers. For this purpose we developed a set of new markers and used them along with markers published for P. humuli by other authors. While the 11 microsatellites that were reported as polymorphic for North America did not show variation for the European samples, the five markers newly established in this study were variable and could be used to investigate the population structure of hop downy mildew in Europe. The overall genetic variation found in European populations was low, with only few heterozygous loci detected. Overall, 20 multilocus genotypes were observed, which clustered into 2 or 4 groups, depending on clustering criteria. We observed a random distribution of genotypes on the surveyed area in line with predominant selfing and long range dispersal. Thus, our investigations suggest that Pseudoperonospora humuli forms a large, potentially panmictic population with little local adaptation and frequent long-distance exchanges. This suggests that a wide array of Pseudoperonospora humuli strains should be used in any resistance breeding programs. In addition, the low degree of variation in Europe in contrast to North America suggests that, in line with its report in Europe as late as the 1930‘s, hop downy mildew might be an introduced species in Europe. Whether the introduction occurred from North America or from East Asia needs to be clarified in future studies.

霜霉病病原体的Pseudoperonospora蚜是栽培和野生啤酒花（的重大疾病啤酒花在世界上许多的啤酒花种植区）。尽管它的发生频繁并产生了经济影响，但到目前为止，关于其种群结构的了解还很少，这将是了解种群动态和成功进行抗性育种工作的前提。我们在阿尔卑斯山附近的五个欧洲国家（奥地利，捷克共和国，法国，德国，意大利），一个高山山脉和一个已知的主要传播障碍收集了70株腐殖质样本，并用微卫星标记进行了研究。为此，我们开发了一组新标记，并将其与为腐植假单胞菌发布的标记一起使用由其他作者。尽管在北美被报道为多态的11个微卫星没有显示出欧洲样品的变异，但这项研究中新建立的5个标记是可变的，可用于调查欧洲蛇麻草霉菌的种群结构。在欧洲人群中发现的总体遗传变异较低，仅检测到很少的杂合基因座。总体上，观察到20个多基因座基因型，根据聚类标准分为2或4组。我们观察到的基因型在调查区域的随机分布与主要的自交和远距离散布相一致。因此，我们的研究表明，假单胞菌形成了一个大型的，潜在的恐慌人口，几乎没有本地适应性，并且频繁进行长途交流。这表明在任何抗性育种计划中都应使用多种假单孢菌。此外，与北美相比，欧洲的变异程度较低，这表明，根据其在1930年代末在欧洲的报道，啤酒花霜霉病可能是欧洲的一种引进物种。引入是从北美还是从东亚来进行的，都需要在以后的研究中加以澄清。