The <i>Erysiphe alphitoides</i> complex (powdery mildews) – unravelling the phylogeny and taxonomy of an intricate assemblage of species

Powdery mildews on oaks, caused by <i>Erysiphe</i> species, have serious ecological consequences on a range of <i>Quercus</i> hosts. In addition to <i>Erysiphe quercicola</i>, <i>E. alphitoides</i> is one of the most common and widespread species of <i>Erysiphe</i> having a wide host range among oak species, and a clear economic significance in applied ecology, forestry, and forest pathology. There are many publications addressing these important tree pathogens. Previous phylogenetic examinations have shown that <i>E. alphitoides</i> refers to a complicated species assemblage with insufficient taxonomic resolution in ITS + 28S analyses; the associated sequences form an insufficiently resolved species complex. The majority of species within the <i>E. alphitoides</i> complex cannot be unequivocally identified based solely on ITS + 28S analyses. Most of the additional species of the <i>E. alphitoides</i> complex are distributed in Asia, with a concentration in Japan. The question posed is whether there is a single widespread powdery mildew species, <i>E. alphitoides,</i> or an assemblage of closely allied species. To answer this question, specimens of related recognized species, particularly those from Japan, have been subjected to phylogenetic multilocus examinations, including <i>CAM</i>, <i>GAPDH</i>, <i>GS</i>, ITS + 28S, <i>RPB2</i>, and <i>TUB</i> sequences. An analysis of the concatenated sequences resulted in the confirmation of several distinct species. These species form highly supported clades that include <i>E. alphitoides</i>, <i>E. aucubae</i>, <i>E. euonymicola</i>, <i>E. ipomoeae</i>, <i>E. menispermi</i> var. <i>dahurica</i>, <i>E. orixae</i>, <i>E. pseudolonicerae</i>, <i>E. sinomenii</i> and <i>E. wallrothii</i>. <i>Erysiphe akebiae</i> as well as the relationship between Japanese and North American collections requires further examinations.栎树上由叉丝壳属（Erysiphe）物种引起的白粉病，可对多种栎属（Quercus）寄主造成严重的生态危害。除栎生叉丝壳（Erysiphe quercicola）外，浅白叉丝壳（Erysiphe alphitoides）是最为常见且分布广泛的叉丝壳属物种之一，其寄主范围涵盖多种栎树，在应用生态学、林业以及森林病理学领域具有明确的经济重要性。目前已有大量文献针对这类重要的树木病原菌展开研究。此前的系统发育分析显示，浅白叉丝壳（Erysiphe alphitoides）是一个分类分辨率不足的复杂物种类群，在ITS+28S序列分析中无法得到清晰区分，其相关序列构成了一个分辨率不足的物种复合群。浅白叉丝壳复合群中的多数物种无法仅通过ITS+28S序列分析得到明确鉴定。该复合群的多数新增物种分布于亚洲，且在日本较为集中。当前存在的核心问题是：究竟存在单一广泛分布的白粉菌物种——浅白叉丝壳（Erysiphe alphitoides），还是一类亲缘关系紧密的物种复合体？为解答这一问题，研究人员对相关已认定物种的标本（尤其是来自日本的标本）开展了多位点系统发育分析，所涉及的序列包括CAM、GAPDH、GS、ITS+28S、RPB2以及TUB。对拼接序列的分析证实了多个独立物种的存在，这些物种形成了高支持度的演化支，其中包括浅白叉丝壳（Erysiphe alphitoides）、桃叶珊瑚叉丝壳（Erysiphe aucubae）、卫矛生叉丝壳（Erysiphe euonymicola）、番薯叉丝壳（Erysiphe ipomoeae）、防己叉丝壳达乌里变种（Erysiphe menispermi var. dahurica）、常山叉丝壳（Erysiphe orixae）、假忍冬叉丝壳（Erysiphe pseudolonicerae）、青藤叉丝壳（Erysiphe sinomenii）以及瓦尔特叉丝壳（Erysiphe wallrothii）。三叶木通叉丝壳（Erysiphe akebiae）以及日本与北美采集标本间的亲缘关系，仍有待进一步研究。