Hansen E M, Streito Jean-Claude, Delatour Claude
Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331.
Laboratoire National de la Protection des Vegetaux, Nancy, France.
Plant Dis. 1999 Jun;83(6):587. doi: 10.1094/PDIS.1999.83.6.587B.
Phytophthora lateralis, a pathogen of Chamaecyparis lawsoniana (Port-Orford cedar or Lawson's cypress), was confirmed in France, but isolates from Germany identified as P. lateralis or "similar to" P. lateralis proved to be P. gonapodyides. Previously, P. lateralis was known only from western North America, where it has been destructive in nurseries, ornamental plantings, and the forest since its introduction about 1920 (1). Reports from other locations have proved to be misidentifications or impossible to confirm. In France, P. lateralis was isolated and identified from C. lawsoniana on two occasions (1996 and 1998) in different parts of the country, probably stemming from a single original infestation of young, potted, greenhouse-propagated cedars in a commercial nursery. German isolates were from an old culture collection and from irrigation water in a nursery growing a wide range of woody ornamentals. Identifications were confirmed by comparison (2) with authentic isolates. P. lateralis isolates from France and Oregon formed laterally proliferating, elongated obpyriform sporangia that under the conditions of our tests could be dislodged by agitation, leaving a short pedicel. Also, brown chlamydospores formed laterally on the hyphae or terminally on a short stalk and oospores were not formed on standard media. Radial growth was about 2 mm per day. In contrast, sporangia of German isolates and known P. gonapodyides isolates were similar. They exhibited nested pro liferation, were broader than P. lateralis sporangia, and were not readily dehiscent. Some P. gonapodyides isolates, including those from Germany, formed chlamydospores, but these were nearly all catenulate and not lateral, and isolates grew faster (3 to 4 mm per day). Pathogenicity was tested by stem inoculation of C. lawsoniana. P. lateralis from France and Oregon produced lesions averaging 4.7 cm after 2 months (range 2.0 to 8.1 cm, six replicates per isolate, five isolates) while the six replicates of the two German isolates averaged 1.2- and 1.6-cm lesion lengths. Furthermore, sequences of internal transcribed spacer (ITS) DNA from French and Oregon P. lateralis isolates were identical, while sequences of German isolates were similar to P. gonapodyides (J. Duncan and D. Cooke, personal communiation). P. lateralis is a dangerous pathogen of C. lawsoniana and is also pathogenic to Taxus spp. (1), although less aggressive on this host. If established, it would be a serious threat to the widespread ornamental plantings and scattered forest plantations of C. lawsoniana in Europe. References: (1) E. M. Hansen and K. J. Lewis. Compendium of Conifer Diseases. American Phytopathological Society, 1997. (2) C. M. Tucker and J. A. Milbrath. Mycologia 34:94, 1942.
樟疫霉（Phytophthora lateralis）是美国扁柏（Chamaecyparis lawsoniana，又称俄勒冈白扁柏或劳森扁柏）的一种病原菌，已在法国得到确认，但来自德国的被鉴定为樟疫霉或“类似于”樟疫霉的分离株经证实是栖水疫霉（P. gonapodyides）。此前，樟疫霉仅在北美西部被发现，自1920年左右引入以来，它在苗圃、观赏植物种植园和森林中造成了严重破坏（1）。其他地区的报告后来被证明是误认或无法证实。在法国，曾两次（1996年和1998年）从该国不同地区的美国扁柏中分离并鉴定出樟疫霉，这可能源于商业苗圃中一批年轻的、盆栽的、在温室中繁殖的扁柏最初受到的单一侵染。德国的分离株来自一个旧的菌种保藏库以及一个种植多种木本观赏植物的苗圃的灌溉水。通过与正宗分离株进行比较（2），确认了鉴定结果。来自法国和俄勒冈州的樟疫霉分离株形成侧向增殖的、细长的倒梨形孢子囊，在我们的测试条件下，通过振荡可以使其脱落，留下短柄。此外，褐色厚垣孢子在菌丝上侧向形成或在短柄末端形成，在标准培养基上不形成卵孢子。径向生长速度约为每天2毫米。相比之下，德国分离株和已知的栖水疫霉分离株的孢子囊相似。它们表现出嵌套增殖，比樟疫霉的孢子囊更宽，且不易开裂。一些栖水疫霉分离株，包括来自德国的那些，形成厚垣孢子，但这些几乎都是链状的，而非侧向形成，并且分离株生长更快（每天3至4毫米）。通过对美国扁柏进行茎部接种来测试致病性。来自法国和俄勒冈州 的樟疫霉在2个月后产生的病斑平均长度为4.7厘米（范围为2.0至8.1厘米，每个分离株6个重复，共5个分离株），而两个德国分离株的6个重复的病斑长度平均分别为1.2厘米和1.6厘米。此外，来自法国和俄勒冈州的樟疫霉分离株的内部转录间隔区（ITS）DNA序列相同，而德国分离株的序列与栖水疫霉相似（J. 邓肯和D. 库克，个人交流）。樟疫霉是美国扁柏的一种危险病原菌，对红豆杉属植物（Taxus spp.）也具有致病性（1），尽管对该寄主的侵染力较弱。如果它在欧洲定殖，将对欧洲广泛种植的美国扁柏观赏植物和分散的森林种植园构成严重威胁。参考文献：（1）E. M. 汉森和K. J. 刘易斯。《针叶树病害简编》。美国植物病理学会，1997年。（2）C. M. 塔克和J. A. 米尔布拉思。《真菌学》34:94，1942年。
