Hüberli D, Ivors K L, Smith A, Tse J G, Garbelotto M
Department of ESPM-ES, 151 Hilgard Hall, University of California, Berkeley 94720.
Plant Dis. 2005 Feb;89(2):204. doi: 10.1094/PD-89-0204C.
In May 2003, Phytophthora ramorum S. Werres & A.W.A.M. de Cock was isolated from the leaf tips of a single plant of false Solomon's seal (Maianthemum racemosum (L.) Link, formely known as Smilacina racemosa (L.) Desf.), a native, herbaceous perennial of the Liliaceae family, at the Jack London State Park in Sonoma County, California. Affected leaves had cream-to-brown lesions on the tips that were delimited by a yellow chlorotic zone. Lesions on the stems were not observed. The isolate (American Type Culture Collection [ATCC], Manassas, VA, MYA-3280; Centraal Bureau voor Schimmelcultures, Baarn, the Netherlands, CBS 114391) was typical of P. ramorum with large chlamydospores and caduceus, semipapillate sporangia, and the sequence (GenBank Accession No. AY526570) of the internal transcribed spacer region of the rDNA matched those published previously (4). The site, from which wood rose (Rosa gymnocarpa) was recently identified as a host, is a mixed forest containing confirmed P. ramorum-infected coast redwood (Sequoia sempervirens), California bay laurel (Umbellularia californica), and tanoak (Lithocarpus densiflora) trees (2,3). Two leaves per asymptomatic, pesticide free, potted plant of false Solomon's seal were inoculated with zoospores of the P. ramorum isolate obtained from infected false Solomon's seal (1). Five plants were inoculated in trial 1, and the following day, three plants were inoculated in trial 2. A control leaf of each plant was dipped in sterile deionized water. Plants were enclosed in plastic bags, misted regularly with sterile distilled water, and maintained at 16 to 21°C in the greenhouse. In both trials, plants did not have lesions on the leaves after 16 days and were reinoculated on separate days for each trial with higher concentrations of zoospores (1 × 10 [trial 1] and 2 × 10 [trial 2] zoospores/ml). Cream-colored lesions, similar to those observed in the field, were evident 1 week after the second inoculation and stopped progressing in both trials by 17 days. Lesions starting from the leaf tips averaged 13 mm (range 8 to 24 mm) long, and P. ramorum was reisolated on Phytophthora-selective agar medium modified with 25 mg of pentachloronitrobenzene from 44% (trial 1) and 83% (trial 2) of all lesions (4). Control leaves had no lesions, and P. ramorum was not reisolated. Sporangia were not observed on any leaves when examined with the dissecting microscope. The fact that lesions developed only after a second inoculation with higher concentrations of zoospores, and these lesions stopped progressing after 17 days, suggests that false Solomon's seal is much less susceptible than other hosts such as western starflower (Trientalis latifolia) (1) and wood rose (2). To our knowledge, this is the first report of a plant from the Liliaceae as a natural host for P. ramorum, although Smilax aspersa was identified as being susceptible in artificial inoculations of detached leaves (E. Moralejo and L. Hernández, personal communication). False Solomon's seal is popular in the horticultural industry. References: (1) D. Hüberli et al. Plant Dis. 87:599, 2003. (2) D. Hüberli et al. Plant Dis. 88:430, 2004. (3) P. E. Maloney et al. Plant Dis. 86:1274, 2002. (4) D. M. Rizzo et al. Plant Dis. 86:205, 2002.
2003年5月，在加利福尼亚州索诺马县的杰克·伦敦州立公园，从一株延龄草（Maianthemum racemosum (L.) Link，原名为Smilacina racemosa (L.) Desf.）的叶尖分离出了樟疫霉（Phytophthora ramorum S. Werres & A.W.A.M. de Cock），延龄草是百合科的一种本土多年生草本植物。受感染的叶片叶尖有米色至褐色的病斑，病斑由黄色褪绿带界定。未观察到茎上有病斑。该分离株（美国典型培养物保藏中心[ATCC]，弗吉尼亚州马纳萨斯，MYA - 3280；荷兰巴恩的真菌菌种保藏中心，CBS 114391）是典型的樟疫霉，具有大型厚垣孢子和双色体、半乳头状孢子囊，核糖体DNA内部转录间隔区的序列（GenBank登录号AY526570）与先前发表的序列相符(4)。该地点最近被确定为木香蔷薇（Rosa gymnocarpa）的寄主，是一片混交林，其中含有已证实感染樟疫霉的海岸红杉（Sequoia sempervirens）、加州月桂树（Umbellularia californica）和鞣皮栎（Lithocarpus densiflora）树(2,3)。从受感染的延龄草中获得的樟疫霉分离株的游动孢子接种到每株无症状、未施农药的盆栽延龄草的两片叶子上(1)。试验1接种了5株植物，第二天，试验2接种了3株植物。每株植物的一片对照叶浸入无菌去离子水中。将植物装入塑料袋中，定期用无菌蒸馏水喷雾，并在温室中保持在16至21°C。在两个试验中，16天后植物叶片上均未出现病斑，并且在每个试验的不同日期用更高浓度的游动孢子（试验1为1×10，试验2为2×10个游动孢子/毫升）再次接种。第二次接种1周后出现了与田间观察到的相似的米色病斑，两个试验中病斑在17天后停止扩展。从叶尖开始的病斑平均长13毫米（范围为8至24毫米），并且从所有病斑的44%（试验1）和83%（试验2）中，在添加了25毫克五氯硝基苯的疫霉选择性琼脂培养基上重新分离出了樟疫霉(4)。对照叶没有病斑，也未重新分离出樟疫霉。用解剖显微镜检查时，在任何叶片上均未观察到孢子囊。病斑仅在第二次用更高浓度的游动孢子接种后才出现，并且这些病斑在17天后停止扩展，这一事实表明延龄草比其他寄主如西部七瓣莲（Trientalis latifolia）(1)和木香蔷薇(2)更不易感。据我们所知，这是关于百合科植物作为樟疫霉天然寄主的首次报道，尽管在离体叶片的人工接种中已确定糙叶菝葜（Smilax aspersa）易感（E. Moralejo和L. Hernández，个人交流）。延龄草在园艺行业很受欢迎。参考文献：(1) D. Hüberli等人，《植物病害》87:599，2003年。(2) D. Hüberli等人，《植物病害》88:430，2004年。(3) P. E. Maloney等人，《植物病害》86:1274，2002年。(4) D. M. Rizzo等人，《植物病害》86:205，2002年。
