University of Hohenheim, Institute of Botany 210, D-70593 Stuttgart, Germany.
IMA Fungus. 2011 Dec;2(2):163-71. doi: 10.5598/imafungus.2011.02.02.07. Epub 2011 Nov 11.
Pathogens belonging to the Oomycota, a group of heterokont, fungal-like organisms, are amongst the most notorious pathogens in agriculture. In particular, the obligate biotrophic downy mildews and the hemibiotrophic members of the genus Phytophthora are responsible for a huge variety of destructive diseases, including sudden oak death caused by P. ramorum, potato late blight caused by P. infestans, cucurbit downy mildew caused by Pseudoperonospora cubensis, and grape downy mildew caused by Plasmopara viticola. About 800 species of downy mildews and roughly 100 species of Phytophthora are currently accepted, and recent studies have revealed that these groups are closely related. However, the degree to which Phytophthora is paraphyletic and where exactly the downy mildews insert into this genus in relation to other clades could not be inferred with certainty to date. Here we present a molecular phylogeny encompassing all clades of Phytophthora as represented in a multi-locus dataset and two representatives of the monophyletic downy mildews from divergent genera. Our results demonstrate that Phytophthora is at least six times paraphyletic with respect to the downy mildews. The downy mildew representatives are consistently nested within clade 4 (contains Phytophthora palmivora), which is placed sister to clade 1 (contains Phytophthora infestans). This finding would either necessitate placing all downy mildews and Phytopthora species in a single genus, either under the oldest generic name Peronospora or by conservation the later name Phytophthora, or the description of at least six new genera within Phytophthora. The complications of both options are discussed, and it is concluded that the latter is preferable, as it warrants fewer name changes and is more practical.
属于卵菌门（一种真菌样的异质生物）的病原体是农业中最臭名昭著的病原体之一。特别是专性生物营养型霜霉病和半生物营养型疫霉属的成员，它们导致了各种各样的破坏性疾病，包括由 P. ramorum 引起的突发性橡树死亡、由 P. infestans 引起的马铃薯晚疫病、由 Pseudoperonospora cubensis 引起的葫芦霜霉病和由 Plasmopara viticola 引起的葡萄霜霉病。目前，约有 800 种霜霉病和大约 100 种疫霉被接受，最近的研究表明这些群体密切相关。然而，迄今为止，还不能确定疫霉的分支程度以及霜霉病在该属中相对于其他分支的确切位置。在这里，我们提出了一个分子系统发育，涵盖了多基因座数据集所代表的所有疫霉属的分支和来自不同属的单系霜霉病的两个代表。我们的结果表明，相对于霜霉病，疫霉属至少是六倍的并系。霜霉病代表始终嵌套在第 4 分支（包含 P. palmivora）中，该分支与第 1 分支（包含 P. infestans）并列。这一发现要么需要将所有的霜霉病和疫霉属物种置于一个单独的属中，要么使用最古老的属名 Peronospora，要么通过保留后来的属名 Phytophthora，或者在 Phytophthora 中至少描述六个新属。这两种选择的复杂性都进行了讨论，并得出结论认为后者更可取，因为它需要更少的名称更改，更具实用性。
