ABSTRACT Marine species of the oomycete genus Olpidiopsis that infect cultivated red macroalgae, most notably Pyropia spp., are one of the main causes of economic loss in the Asian seaweed industry. We recently described novel Olpidiopsis species infecting red algae in Scotland, and thus hypothesized that this genus is more abundant and widespread than previously recognized. Here, we show that the eukaryotic microbiome of macroscopically healthy Porphyra umbilicalis thalli frequently contains marker genes closely related to Olpidiopsis. Thanks to a custom pipeline that allows for de novo OTU and biogeography discovery, and the recovery of precomputed OTUs from large-scale metabarcoding campaigns, we unveil more than 20 unknown Olpidiopsis taxa with a worldwide distribution. Additionally, laboratory-controlled cross-infection experiments show that a Scottish variety of O. porphyrae is virulent on the most commonly cultivated Pyropia yezoensis cultivar in Korea and that conversely, a Korean strain of O. porphyrae successfully infects wild Bangia sp. strains isolated from Scotland. These results provide proof-of-concept that a native Olpidiopsis pathogen may threaten an introduced crop or that an Olpidiopsis pathogen potentially introduced alongside a non-native crop might cross-infect a native European alga. Thus, we draw parallels with several current biosecurity crises, where major risks to native floras and faunas, as well as crops, are caused by the inadvertent introduction of poorly known pathogens through the agricultural and horticultural trades. Therefore, we express concern that the rapid growth of algal cultivation worldwide, linked to international movement of seaweed seed and the absence of biosecurity monitoring or reulation pertaining to this trade, potentially lays the ground for grave ecological and economic crises in the marine environment.

中文翻译：

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卵菌属 Olpidiopsis 的隐藏多样性对全世界红藻的培育和保护构成潜在危害

摘要 卵菌属 Olpidiopsis 的海洋物种感染栽培的红色大型藻类，最显着的是 Pyropia spp.，是亚洲海藻产业经济损失的主要原因之一。我们最近描述了在苏格兰感染红藻的新 Olpidiopsis 物种，因此假设该属比以前认识的更丰富和广泛。在这里，我们表明宏观健康的脐紫菜菌体的真核微生物组经常包含与 Olpidiopsis 密切相关的标记基因。得益于允许从头 OTU 和生物地理学发现的自定义管道，以及从大规模元条形码活动中恢复预先计算的 OTU，我们揭示了 20 多个未知的 Olpidiopsis 分类群，分布于世界各地。此外，实验室控制的交叉感染实验表明，一种苏格兰的 O. porphyrae 品种对韩国最常种植的 Pyropia yezoensis 品种具有毒性，相反，一种韩国的 O. porphyrae 菌株成功感染了野生 Bangia sp。从苏格兰分离的菌株。这些结果提供了一个概念证明，即本地 Olpidiopsis 病原体可能威胁引入的作物，或者可能与非本地作物一起引入的 Olpidiopsis 病原体可能交叉感染欧洲本土藻类。因此，我们将当前的几场生物安全危机进行了比较，在这些危机中，本地动植物群以及农作物的主要风险是由于通过农业和园艺贸易无意引入鲜为人知的病原体造成的。所以，