Phytophthora ×stagnum nothosp. nov., a New Hybrid from Irrigation Reservoirs at Ornamental Plant Nurseries in Virginia

A novel Phytophthora species was frequently recovered from irrigation reservoirs at several ornamental plant production facilities in eastern Virginia. Initial sequencing of the internal transcribed spacer (ITS) region of this species generated unreadable sequences due to continual polymorphic positions. Cloning and sequencing the ITS region as well as sequencing the mitochondrially encoded cytochrome c oxidase 1 and beta-tubulin genes revealed that it is a hybrid between P. taxon PgChlamydo as its paternal parent and an unknown species genetically close to P. mississippiae as its maternal parent. This hybrid has some diagnostic morphological features of P. taxon PgChlamydo and P. mississippiae. It produces catenulate hyphal swellings, characteristic of P. mississippiae, and chlamydospores, typical of P. taxon PgChlamydo. It also produces both ornamented and relatively smooth-walled oogonia. Ornamented oogonia are another important diagnostic character of P. mississippiae. The relatively smooth-walled oogonia may be indicative of oogonial character of P. taxon PgChlamydo. The new hybrid is described here as Phytophthora ×stagnum.研究团队从弗吉尼亚州东部多家观赏植物生产设施的灌溉水库中，频繁分离得到一种新的疫霉属（Phytophthora）物种。对该物种的内部转录间隔区（internal transcribed spacer, ITS）进行初始测序时，因存在持续的多态性位点，所得测序结果无法读取。通过对ITS区域进行克隆测序，以及对线粒体编码的细胞色素c氧化酶1（cytochrome c oxidase 1, COX1）和β-微管蛋白（beta-tubulin）基因进行测序，结果表明该物种为杂交起源：其父本为PgChlamydo类群疫霉（P. taxon PgChlamydo），母本为遗传上与密西西比疫霉（P. mississippiae）相近的未知物种。该杂交种兼具PgChlamydo类群疫霉与密西西比疫霉的部分诊断性形态特征：其产生链状菌丝膨大体——这是密西西比疫霉的典型特征，同时产生厚垣孢子——这是PgChlamydo类群疫霉的典型特征。该杂交种还可同时产生具纹饰藏卵器与相对光滑壁的藏卵器。具纹饰藏卵器是密西西比疫霉的另一重要诊断性状，而相对光滑壁的藏卵器则可能体现了PgChlamydo类群疫霉的藏卵器性状。本文将该新杂交种正式描述为Phytophthora ×stagnum。