Seto K, Van den Wyngaert S, Degawa Y, Kagami M
Sugadaira Research Station, Mountain Science Center, University of Tsukuba, 1278-294, Sugadaira-Kogen, Ueda, Nagano 386-2204, Japan.
Department of Environmental Science, Faculty of Science, Toho University, 2-2-1, Miyama, Funabashi, Chiba 274-8510, Japan.
Fungal Syst Evol. 2020 Jun;5:17-38. doi: 10.3114/fuse.2020.05.02. Epub 2019 Aug 21.
During the last decade, the classification system of chytrids has dramatically changed based on zoospore ultrastructure and molecular phylogeny. In contrast to well-studied saprotrophic chytrids, most parasitic chytrids have thus far been only morphologically described by light microscopy, hence they hold great potential for filling some of the existing gaps in the current classification of chytrids. The genus is characterized by an operculate zoosporangium and a resting spore formed as a result of sexual reproduction in which a male thallus and female thallus fuse via a conjugation tube. All described species of are parasites of algae and their taxonomic positions remain to be resolved. Here, we examined morphology, zoospore ultrastructure, host specificity, and molecular phylogeny of seven cultures of spp. Based on thallus morphology and host specificity, one culture was identified as parasitic on zygnematophycean green algae, whereas the others were identified as parasites of diatoms, on , on , and on (formerly ). According to phylogenetic analysis, was separated into two distinct order-level novel lineages; one lineage was composed singly of , which is the type species of the genus, and the other included the three species of diatom parasites. Zoospore ultrastructural observation revealed that the two lineages can be distinguished from each other and both possess unique characters among the known orders within the . Based on these results, we accommodate the three diatom parasites, , , and in the distinct genus , and propose two new orders: and .
在过去十年中，基于游动孢子超微结构和分子系统发育，壶菌的分类系统发生了巨大变化。与研究充分的腐生壶菌不同，大多数寄生壶菌迄今为止仅通过光学显微镜进行了形态学描述，因此它们在填补当前壶菌分类中一些现有空白方面具有巨大潜力。该属的特征是具有一个有盖的游动孢子囊和一个由有性生殖形成的休眠孢子，其中雄体和雌体通过接合管融合。所有已描述的该属物种都是藻类寄生虫，它们的分类地位仍有待确定。在这里，我们研究了七种该属物种培养物的形态、游动孢子超微结构、宿主特异性和分子系统发育。根据菌体形态和宿主特异性，一种培养物被鉴定为寄生在双星藻纲绿藻上的该属物种，而其他培养物被鉴定为硅藻寄生虫，一种寄生在 上，一种寄生在 上，一种寄生在 （原 ）上。根据系统发育分析，该属被分为两个不同的目级新谱系；一个谱系仅由该属的模式种 组成，另一个包括三种硅藻寄生虫。游动孢子超微结构观察表明，这两个谱系可以相互区分，并且在已知的壶菌目内都具有独特的特征。基于这些结果，我们将三种硅藻寄生虫 、 和 归入不同的属 ，并提出两个新目： 和 。
