U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS), Mycology and Nematology Genetic Diversity and Biology Laboratory, Beltsville, MD 20705; Oak Ridge Institute for Science and Education, ARS Research Participation Program, MC-100-44, Oak Ridge, TN 37831; and Department of Plant Biology, Rutgers University, New Brunswick, NJ 08901.
USDA-ARS, Mycology and Nematology Genetic Diversity and Biology Laboratory, Beltsville, MD 20705; and Oak Ridge Institute for Science and Education, ARS Research Participation Program, MC-100-44, Oak Ridge, TN 37831.
Plant Dis. 2018 Dec;102(12):2411-2420. doi: 10.1094/PDIS-01-18-0077-RE. Epub 2018 Sep 24.
Impatiens downy mildew (IDM) of cultivated Impatiens walleriana has had a significant economic impact on the ornamental horticulture industry in the United States and globally. Although recent IDM outbreaks started in 2003, downy mildews on noncultivated Impatiens species have been documented since the 1880s. To understand the relationship between the pathogen causing recent epidemics and the pathogen historically present in the United States, this work characterized genetic variation among a collection of 1,000 samples on 18 plant hosts. Samples included collections during recent IDM epidemics and historical herbarium specimens. Ten major genotypes were identified from cloned rDNA amplicon sequencing and endpoint SNP genotyping. Three genotypes accounted for >95% of the samples, with only one of these three genotypes found on samples predating recent IDM outbreaks. Based on phylogenetic analysis integrating data from three markers and the presence of individual genotypes on multiple Impatiens species, there was some evidence of pathogen-specific infection of I. noli-tangere, but the distinction between genotypes infecting I. walleriana and I. balsamina was not upheld. Overall, this work provides evidence that the majority of rDNA genotypes recovered from recent IDM epidemics are different from historical U.S. genotypes, and that these genotypes can infect Impatiens spp. other than I. walleriana.
栽培凤仙花疫病（IDM）对美国和全球的观赏园艺产业造成了重大的经济影响。尽管最近的 IDM 爆发始于 2003 年，但自 19 世纪 80 年代以来，非栽培凤仙花种上的霜霉病就有记录。为了了解导致近期流行的病原体与历史上在美国存在的病原体之间的关系，本研究对 18 种植物宿主上的 1000 个样本的遗传变异进行了特征描述。样本包括最近 IDM 流行期间的采集和历史标本。通过克隆 rDNA 扩增子测序和终点 SNP 基因分型，鉴定出 10 个主要基因型。有 3 个基因型占样本的 95%以上，其中只有一个基因型在最近 IDM 爆发之前的样本中发现。基于整合了来自三个标记的数据分析和单个基因型在多个凤仙花种上的存在，有一些证据表明病原体对 I. noli-tangere 的特异性感染，但感染 I. walleriana 和 I. balsamina 的基因型之间的区别并没有得到支持。总的来说，这项工作提供了证据表明，从最近的 IDM 流行中恢复的大多数 rDNA 基因型与美国历史基因型不同，并且这些基因型可以感染除 I. walleriana 以外的凤仙花属植物。
