Petrželová I, Kitner M, Doležalová I, Ondřej V, Lebeda A
Centre of the Region Haná for Biotechnological and Agricultural Research, Dept. of Genetic Resources for Vegetables, Medicinal and Special Plants, Crop Research Institute, Šlechtitelů 29, Olomouc, CZ-78371, Czech Republic.
Palacký University in Olomouc, Faculty of Science, Department of Botany, Šlechtitelů 11, Olomouc, CZ-78371, Czech Republic.
Plant Dis. 2015 Mar;99(3):418. doi: 10.1094/PDIS-06-14-0613-PDN.
Sweet basil (Ocimum basilicum L.) is an annual aromatic and medicinal plant in the Lamiaceae that is originally native to India but is grown in warm regions all over the world. It is a popular culinary herb used fresh and dried, and is used in traditional folk medicine. In the Czech Republic, sweet basil is grown commercially in South Moravia or by home gardeners as a potted plant. In 2012, severe downy mildew was observed in a field of basil plants (cv. Dark Green) at the Crop Research Institute (CRI) in Olomouc, Czech Republic. Infected leaves each exhibited large, interveinal, chlorotic lesions, and violet-gray, fuzzy growth on the lower leaf surface. Within a few days, lesions turned necrotic and severely infected leaves dropped prematurely. Microscopic observations revealed hyaline conidiophores typical of Peronospora Corda, emerging from stomata. Conidiophores (n = 100) were usually 239.9 to 296.5 × 8.7 to 10.6 μm, straight, and were branched 4 or 5 times submonopodially at the upper ends. Ultimate branchlets (n = 100) were slightly curved and obtuse, with the longer branchlets usually 17.8 to 22.7 μm and the shorter branchlets 10.0 to 12.9 μm, and each bearing a single conidium. Conidia (n = 100) were olive-brown, mostly ellipsoidal to subglobose, and typically 29.0 to 31.0 × 23.2 to 25.4 μm, with a length/width ratio of 1.2 to 1.3. Oospores were not observed. Based on these morphological characteristics, the pathogen was identified as Peronospora belbahrii Thines (5). The specimen was deposited in a local herbarium at the CRI in Olomouc, as voucher PB-1. Genomic DNA was extracted from conidia, and the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) amplified with primers DC-6 (1) and LR-0 (4). A sequence was deposited in the NCBI database (GenBank Accession No. KJ960193). A BLAST search of the NCBI database revealed 99% identity to the deposited ITS sequences of P. belbahrii from basil and other host species (EU863410, FJ394334-7, GQ390794, GQ390795, HM462241, HM462242, HM486901, HQ702191, HQ730979, KC756923, KF419289, and KF419290). P. belbahrii was first described by Thines et al. (5) as a pathogen of sweet basil and coleus (Solenostemon scutellarioides), but can also infect Agastache spp. (2). There are many reports indicating the pathogen is spreading throughout the world (5). In Europe, chronologically, basil downy mildew has been reported from Italy, France, Switzerland, Germany, Hungary, and Cyprus (2,3,5). To our knowledge, this is the first report of natural occurrence of downy mildew on sweet basil in the Czech Republic. References: (1) D. E. L. Cooke et al. Fung. Genet. Biol. 30:17, 2000. (2) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, USDA ARS. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , 16 June 2014. (3) A. Garibaldi et al. Plant Dis. 89:683, 2005. (4) O. Spring et al. Eur. J. Plant Pathol. 114:309, 2006. (5) M. Thines et al. Mycol. Res. 113:532, 2009.
甜罗勒（Ocimum basilicum L.）是唇形科一年生芳香药用植物，原产于印度，但在世界各地的温暖地区均有种植。它是一种广受欢迎的烹饪香草，可新鲜使用或干燥保存，也用于传统民间医学。在捷克共和国，甜罗勒在南摩拉维亚地区进行商业化种植，家庭园艺爱好者也会将其作为盆栽植物种植。2012年，在捷克共和国奥洛穆茨的作物研究所（CRI）的一片罗勒植株（品种为深绿色）田中观察到严重的霜霉病。受感染的叶片上均出现了大的、叶脉间的、褪绿病斑，叶片下表面有紫灰色、毛茸茸的生长物。几天之内，病斑变成坏死状，严重感染的叶片过早掉落。显微镜观察显示，从气孔中长出了典型的霜霉属（Peronospora Corda）透明分生孢子梗。分生孢子梗（n = 100）通常为239.9至296.5×8.7至10.6μm，直形，在上端呈4或5次亚单轴分枝。最终小枝（n = 100）略弯曲且钝圆，较长的小枝通常为17.8至22.7μm，较短的小枝为10.0至12.9μm，每个小枝上着生一个分生孢子。分生孢子（n = 100）为橄榄褐色，大多为椭圆形至近球形，通常为29.0至31.0×23.2至25.4μm，长宽比为1.2至1.3。未观察到卵孢子。基于这些形态特征，该病原菌被鉴定为罗勒霜霉（Peronospora belbahrii Thines）（5）。标本保存在奥洛穆茨作物研究所的当地植物标本馆中，凭证编号为PB - 1。从分生孢子中提取基因组DNA，并用引物DC - 6（1）和LR - 0（4）扩增核糖体DNA（rDNA）的内部转录间隔区（ITS）。一个序列保存在NCBI数据库中（GenBank登录号：KJ960193）。对NCBI数据库进行BLAST搜索发现，与来自罗勒和其他寄主物种的罗勒霜霉的已保存ITS序列（EU863410、FJ394334 - 7、GQ390794、GQ390795、HM462241、HM462242、HM486901、HQ702191、HQ730979、KC756923、KF419289和KF419290）的同一性为99%。罗勒霜霉最早由Thines等人（5）描述为甜罗勒和彩叶草（Solenostemon scutellarioides）的病原菌，但也可感染藿香属（Agastache spp.）（2）。有许多报道表明该病原菌正在全球范围内传播（5）。在欧洲，按时间顺序，意大利、法国、瑞士、德国、匈牙利和塞浦路斯均已报道了罗勒霜霉病（2,3,5）。据我们所知，这是捷克共和国首次关于甜罗勒自然发生霜霉病的报道。参考文献：（1）D. E. L. Cooke等人，《真菌遗传学与生物学》30:17，2000年。（2）D. F. Farr和A. Y. Rossman，《真菌数据库》。美国农业部农业研究局系统真菌学与微生物学实验室。检索自http://nt.ars-grin.gov/fungaldatabases/，2014年6月16日。（3）A. Garibaldi等人，《植物病害》89:683，2005年。（4）O. Spring等人，《欧洲植物病理学杂志》114:309，2006年。（5）M. Thines等人，《真菌研究》113:532，2009年。
