Maloney P E, Rizzo D M, Koike S T, Harnik T Y, Garbelotto M
Department of Plant Pathology, One Shields Ave., University of California, Davis 95616.
University of California Cooperative Extension, 1432 Abbott Street, Salinas.
Plant Dis. 2002 Nov;86(11):1274. doi: 10.1094/PDIS.2002.86.11.1274A.
Phytophthora ramorum S. Werres & A.W.A.M. de Cock was isolated from discolored leaves and cankers on small branches (<0.5 cm in diameter) on 27 coast redwood (Sequoia sempervirens) saplings (2 to17 cm in diameter) at two locations in California (Jack London State Park, Sonoma County and Henry Cowell State Park, Santa Cruz County). Symptoms were observed on branches throughout the crowns of affected trees. Isolates were identified as P. ramorum by their abundant chlamydospores and caducous, semi-papillate sporangia (2) and internal transcribed spacer (ITS) rDNA sequences identical to those of P. ramorum from Quercus spp., Lithocarpus densiflorus, and Rhododendron (1,2). P. ramorum was also detected in dying basal sprouts on mature redwood trees from an additional five locations in coastal California by polymerase chain reaction (PCR) amplification of the ITS region using DNA extracted from symptomatic tissue and P. ramorum-specific PCR primers. To test for pathogenicity, foliage inoculations were conducted on redwood seedlings in two trials by misting 30 leaves per trial (five leaves per seedling plus controls) with sterile distilled water and then pinning inoculum plugs to the upper surface of leaves. Inoculation resulted in lesions of 1 to 20 mm on individual leaves, and P. ramorum was recovered from 43% of inoculated leaves. Symptoms were not restricted to inoculated leaves because 15 inoculations of individual leaves led to discoloration of two or more adjacent leaves. On one inoculation, 60 mm of the adjacent stem was killed. Stems of redwood seedling (approximately 1 cm in diameter) were wound inoculated (1) in two trials consisting of 10 inoculated seedlings per trial plus 10 controls. After 6 weeks, lesion lengths in the cambium caused by P. ramorum averaged 13.7 mm (range 4 to 21 mm). P. ramorum was recovered from 100% of inoculated stems. Entire branches near the inoculation point became chlorotic even though no direct connection was evident between the lesion and the branches. No chlorosis was observed among the control inoculations. Mean lesion lengths of inoculated stems were significantly greater in both trials than those of control inoculations (mean 6.2 mm) at P < 0.05 based on analysis of variance (ANOVA). Redwood saplings (2.5 to 4.5 cm in diameter) were also wound inoculated in a separate trial. No phloem or cambial discoloration was observed after 7 weeks, but necrotic lesions in the xylem had a mean length of 39 mm (range 12 to 73 mm). In addition, narrow streaks, 1 to 2 mm in diameter, were also noted in the xylem extending from the necrotic areas upward to 90 cm. P. ramorum was recovered from 70% of inoculated stems in this trial. Mean lesion lengths of P. ramorum were significantly greater in all trials than those of control inoculations (mean 20 mm) at P < 0.05 based on ANOVA. While P. ramorum causes a lethal canker on Quercus spp. and L. densiflorus (1), we have not observed unusual mortality or disease symptoms on overstory redwoods in natural forests. The impact of infection by P. ramorum on understory redwoods is also unclear. However, the pathogen appears to be able to kill sprouts. References: (1) D. M. Rizzo et al. Plant Dis. 86:205, 2002. (2) S. Werres et al. Mycol. Res. 105:1155, 2001.
从加利福尼亚州两个地点（索诺马县的杰克伦敦州立公园和圣克鲁兹县的亨利考威尔州立公园）的27株海岸红杉（红杉）树苗（直径2至17厘米）上直径小于0.5厘米的变色叶片和小枝溃疡中分离出了樟疫霉（Phytophthora ramorum S. Werres & A.W.A.M. de Cock）。在受影响树木的整个树冠的枝条上都观察到了症状。通过其丰富的厚垣孢子、脱落的半乳头状孢子囊（2）以及与来自栎属植物、密花石栎和杜鹃花的樟疫霉的内部转录间隔区（ITS）rDNA序列相同，将分离物鉴定为樟疫霉（1,2）。通过使用从有症状组织中提取的DNA和樟疫霉特异性PCR引物对ITS区域进行聚合酶链反应（PCR）扩增，还在加利福尼亚沿海另外五个地点的成熟红杉树的濒死基部萌条中检测到了樟疫霉。为了测试致病性，在两项试验中对红杉幼苗进行了叶片接种，每次试验用无菌蒸馏水喷雾30片叶子（每株幼苗5片叶子加对照），然后将接种物菌塞固定在叶片上表面。接种导致单叶上出现1至20毫米的病斑，并且从43%的接种叶片中分离出了樟疫霉。症状不限于接种叶片，因为对单叶进行的15次接种导致两片或更多相邻叶片变色。在一次接种中，相邻茎干60毫米被杀死。在两项试验中对红杉幼苗（直径约1厘米）的茎进行了创伤接种（1），每次试验有10株接种幼苗加10个对照。6周后，樟疫霉在形成层中引起的病斑长度平均为13.7毫米（范围4至21毫米）。从100%的接种茎中分离出了樟疫霉。即使在病斑与枝条之间没有明显的直接连接，接种点附近的整个枝条也变黄了。对照接种中未观察到黄化现象。基于方差分析（ANOVA），在两项试验中接种茎的平均病斑长度均显著大于对照接种（平均6.2毫米），P < 0.05。在另一项试验中也对直径2.5至4.5厘米的红杉树苗进行了创伤接种。7周后未观察到韧皮部或形成层变色，但木质部中的坏死病斑平均长度为39毫米（范围12至73毫米）。此外，在木质部中还注意到从坏死区域向上延伸至90厘米的直径1至2毫米的狭窄条纹。在该试验中从70%的接种茎中分离出了樟疫霉。基于ANOVA，在所有试验中樟疫霉的平均病斑长度均显著大于对照接种（平均20毫米），P < 0.05。虽然樟疫霉在栎属植物和密花石栎上会引起致命溃疡（1），但我们在天然森林的上层红杉中未观察到异常死亡或病害症状。樟疫霉感染对下层红杉的影响也不清楚。然而，该病原菌似乎能够杀死萌条。参考文献：（1）D. M. Rizzo等人，《植物病害》86:205，2002年。（2）S. Werres等人，《真菌学研究》105:1155，2001年。
