Desoignies N, Eickermann M, Delfosse P, Kremer F, Godart N, Hoffmann L, Legrève A
Unité de Phytopathologie, Université Catholique de Louvain, Croix du sud 2 bte 3, B-1348 Louvain-la-Neuve, Belgium.
Centre de Recherche Public-Gabriel Lippmann, 41, Rue du Brill, L-4422 Belvaux, Luxembourg.
Plant Dis. 2009 Nov;93(11):1220. doi: 10.1094/PDIS-93-11-1220B.
Rapeseed (Brassica napus L.) is the third most important crop after wheat and barley in the Grand Duchy of Luxembourg. Since 2005, clubroot symptoms in this crop have been reported by farmers in the Gutland Region. In February 2009, plants of the hybrid rapeseed cv. Exocet, with stunted growth, yellow leaves, and club-shaped roots, were sampled from a field in Oberkorn village near Differdange. Microscopic observations of the rapeseed root fragments revealed the presence of the three life stages characteristic of Plasmodiophora brassicae Woronin. Plasmodia and zoosporangia were observed in the root hairs and resting spores were present in root galls. Individual spores were 2 to 3 μm in diameter. Total DNA was extracted from the root galls with a FAST DNA Kit (MP Biomedicals, Irvine, CA). The internal transcribed spacer region (ITS) and 5.8S gene of the rDNA region were amplified with ITS5 and ITS4 primers as described by White et al. (2) and part of this region was sequenced. A BLASTn search in GenBank revealed that the sequence closely resembled (98% identity) sequences of P. brassicae (Genbank Accession No. EF195335) from an isolate of the pathogen from Switzerland. To confirm the presence of the pathogen, seeds of the susceptible ecotype cvi-0 of Arabidopsis thaliana were grown in a soil sample (1 liter) collected near the infected rapeseed plants. After 55 days of growth in a glasshouse at 15 to 20°C, the roots of 11 plants were analyzed. Two showed clear clubroot symptoms and four others exhibited small swellings. The remaining five plants were symptomless, but plasmodia and zoosporangia were found in root hair cells. Clubroot caused by P. brassicae has previously been described on B. napus and other crucifers (1). To our knowledge, this is the first report of clubroot disease caused by P. brassicae in Luxembourg. Because its presence has since been observed in new fields in the Gutland Region and because of the ability of the pathogen to survive for a long period in the soil, this disease could represent a severe threat for cropping of Brassicaceae in Luxembourg and neighboring countries. References: (1) I. R. Crute et al. Plant Breed. Abstr. 50:91, 1980. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic press: San Diego, 1990.
油菜（Brassica napus L.）是卢森堡大公国继小麦和大麦之后的第三大重要作物。自2005年以来，古特兰地区的农民已报告了这种作物出现根肿病症状。2009年2月，从迪弗丹日附近奥伯科恩村的一块田地中采集了生长发育迟缓、叶片发黄且根部呈棒状的杂交油菜品种Exocet的植株。对油菜根段进行显微镜观察，发现了芸苔根肿菌（Plasmodiophora brassicae Woronin）三个特征性的生活阶段。在根毛中观察到了原质团和游动孢子囊，在根瘤中发现了休眠孢子。单个孢子直径为2至3μm。使用FAST DNA试剂盒（MP Biomedicals，加利福尼亚州欧文市）从根瘤中提取总DNA。按照White等人（2）所述，用ITS5和ITS4引物扩增核糖体DNA区域的内部转录间隔区（ITS）和5.8S基因，并对该区域的一部分进行测序。在GenBank中进行BLASTn搜索发现，该序列与来自瑞士一种病原菌分离株的芸苔根肿菌序列（Genbank登录号EF195335）相似度很高（98%同一性）。为了确认病原菌的存在，将拟南芥敏感生态型cvi-0的种子种植在感染油菜植株附近采集的一份土壤样本（1升）中。在15至20°C的温室中生长55天后，对11株植株的根部进行分析。有两株表现出明显的根肿病症状，另外四株有小的肿胀。其余五株无症状，但在根毛细胞中发现了原质团和游动孢子囊。此前已报道过芸苔根肿菌引起的根肿病发生在甘蓝型油菜和其他十字花科植物上（1）。据我们所知，这是卢森堡首次报道由芸苔根肿菌引起的根肿病。由于此后在古特兰地区的新田地中也观察到了它的存在，并且由于病原菌在土壤中能够长期存活，这种病害可能对卢森堡及周边国家的十字花科作物种植构成严重威胁。参考文献：（1）I. R. Crute等人，《植物育种文摘》50:91，1980年。（2）T. J. White等人，载于《PCR协议：方法与应用指南》，M. A. Innis等人编，学术出版社：圣地亚哥，1990年，第315页。
