Phylogeny and taxonomy of <i>Erysiphe</i> spp. on <i>Rhododendron</i>, with a special emphasis on North American species

The genus Rhododendron comprises over 1000 evergreen and deciduous species. In the Pacific Northwest Coast region of North America (PNWC), powdery mildews infecting deciduous Rhododendron spp. are well documented but less so on evergreen Rhododendron spp. Infections of both groups of hosts historically have been attributed to Erysiphe azaleae or E. vaccinii. No formal characterizations of powdery mildew fungi infecting either deciduous or evergreen Rhododendron spp. in the PNWC have been completed. The objectives of this study were to identify the powdery mildew pathogens infecting evergreen Rhododendron spp. in the PNWC and to assess the phylogenetic position of these fungi within the Erysiphaceae. To ascertain valid taxonomic conclusions, and to determine whether potential introductions of exotic Rhododendron powdery mildews in North America have occurred, it was necessary to put the new North American phylogenetic data into a worldwide context. Therefore, available phylogenetic data from all Erysiphe spp. on Rhododendron have been included in our analyses. Based on analyses of numerous new internal transcribed spacer (ITS) and 28S rDNA sequences and already available sequences deposited in GenBank retrieved from evergreen and deciduous Rhododendron spp., the following Erysiphe spp. could be phylogenetically confirmed (all belonging to Erysiphe sect. Microsphaera): Erysiphe azaleae nom. cons. (Oidium ericinum could be verified as a synonym), E. digitata (holotype sequenced), E. izuensis, and E. vaccinii. Erysiphe azaleae and E. vaccinii are epitypified with sequenced specimens, and an ex-neotype sequence has been obtained for Oidium ericinum. Erysiphe rhododendri (Erysiphe sect. Erysiphe), only known from two collections in India (Himalayan region), was not available for phylogentic analyses.杜鹃花属（Rhododendron）包含逾1000种常绿与落叶类群。在北美太平洋西北沿岸地区（PNWC），已有充分文献记载落叶杜鹃花属植物被白粉菌侵染的案例，但常绿类群的相关报道则较为匮乏。过往研究曾将两类寄主的白粉病均归因于杜鹃花白粉菌（Erysiphe azaleae）或越橘白粉菌（E. vaccinii），但迄今尚未有针对该区域内侵染落叶或常绿杜鹃花的白粉菌开展正式形态与分子特征鉴定的研究。本研究的目标为：鉴定北美太平洋西北沿岸地区侵染常绿杜鹃花的白粉病菌，并明确这些真菌在白粉菌科（Erysiphaceae）中的系统发育地位。为获得可靠的分类学结论，同时明确北美地区是否存在外来杜鹃花白粉菌的引入事件，需将新获取的北美系统发育数据置于全球研究框架下进行分析。因此，本研究纳入了所有已发表的、侵染杜鹃花属植物的白粉菌系统发育数据用于分析。 基于对大量新获取的内转录间隔区（ITS）及28S核糖体DNA（28S rDNA）序列，以及从基因银行（GenBank）中调取的、来源于常绿与落叶杜鹃花属植物的已有序列开展的系统发育分析，本研究从系统发育层面确认了以下白粉菌属（Erysiphe）物种（均隶属于小钩丝壳组（Erysiphe sect. Microsphaera））：杜鹃花白粉菌（Erysiphe azaleae，保留学名（nom. cons.）），其异名欧石南粉孢（Oidium ericinum）已得到验证；掌状白粉菌（E. digitata，主模式标本已完成测序）；伊豆白粉菌（E. izuensis）；以及越橘白粉菌（E. vaccinii）。本研究对杜鹃花白粉菌与越橘白粉菌标定了带测序信息的后选模式标本，并为欧石南粉孢获取了源于新新模式的序列。仅在印度喜马拉雅地区的两份标本中发现的杜鹃白粉菌（Erysiphe rhododendri，隶属于白粉菌组（Erysiphe sect. Erysiphe））未获得用于系统发育分析的可用材料。