Nagy G, Horváth A
Department of Plant Pathology, Corvinus University of Budapest, Hungary. This work was supported by TÁMOP-4.2.1./B-09/1-KMR-2010-0005 Project.
Plant Dis. 2011 Aug;95(8):1034. doi: 10.1094/PDIS-04-11-0329.
Sweet basil (Ocimum basilicum L.) is an important medicinal and aromatic plant in Hungary that is cultivated over a large area. During field surveys conducted in 2010, significant incidence of downy mildew was observed in two plant stands at Budapest-Soroksár and Tordas. In 2003, the disease occurred in a greenhouse at Albertirsa as well. By the end of September, on full-grown leaves of two sweet basil cultivars, the frequency of disease occurrence and the percentage of infected leaf area reached 80 to 90% and 17 to 20%, respectively, at Budapest-Soroksár. Symptoms appeared mainly on cvs. Genovese and Milita among others. On leaves, large chlorotic lesions with soft margins developed, followed by necrotization from the middle. Chlorosis often involved the entire leaf surface. Necrotic spots were irregular, variable in diameter, and limited by the main veins. A typical grayish white furry growth could be observed mainly on abaxial leaf surfaces both in chlorotic and necrotic regions. Most abundant growth developed on the leaves of cv. Genovese. Premature leaf fall on diseased plants occurred as well. The fungus was identified as Peronospora belbahrii Thines on the basis of morphological investigation suggested by Thines et al. (4). Sporangiophores were colorless with a long, straight trunk and monopodially branched five to seven times with a length of 416 to 784 μm (average 572 μm). Sporangiophores ended with two slightly curved acute branchlets, the longer one measured 12.5 to 25.0 μm (average 17.1 μm) and the shorter one measured 5.0 to 18.8 μm (average 9.5 μm) long. Ratio of longer to shorter branchlets was 0.7 to 3.0, the average ratio was 1.9. Sporangia were rounded or slightly ovoid, olive to dark brown, and measured 29.3 × 25.6 (23.8 to35.0 × 20.0 to 31.3 μm). Length/width ratio was 1.2 (1.0 to 1.4). Molecular investigation of two isolates was performed. DNA extraction from sporangiophores was followed by PCR using ITS5 and ITS4 primers. The obtained sequence (GenBank Accession No. HQ702191) showed 99.8 to 100.0% similarity with sequences of P. belbahrii (e.g., Accession Nos. FJ394335 and HN462241) and Peronospora sp. (e.g., Accession Nos. AY884605, AY919301, and FJ346561) isolated from sweet basil. In Europe, the disease was reported from Italy (2), France (3), Germany (4), and Switzerland (1). To our knowledge, this is the first report of downy mildew on sweet basil in Hungary. References: (1) L. Belbahri et al. Mycol. Res. 109:1276, 2005. (2) A. Garibaldi et al. Plant Dis. 88:312, 2004. (3) A. Garibaldi et al. Plant Dis. 89:683, 2005. (4) M. Thines et al. Mycol. Res. 113:532, 2009.
甜罗勒（Ocimum basilicum L.）是匈牙利一种重要的药用和芳香植物，种植面积广泛。在2010年进行的田间调查中，在布达佩斯 - 索罗克萨尔和托尔达斯的两个种植地观察到霜霉病的发病率很高。2003年，阿尔贝蒂尔萨的一个温室中也出现了这种病害。到9月底，在布达佩斯 - 索罗克萨尔的两个甜罗勒品种的成熟叶片上，病害发生频率和感染叶面积百分比分别达到80%至90%和17%至20%。症状主要出现在热那亚和米利塔等品种上。叶片上出现边缘柔软的大型褪绿病斑，随后从中间开始坏死。褪绿通常涉及整个叶片表面。坏死斑点不规则，直径可变，受主脉限制。在褪绿和坏死区域的叶片背面，主要可以观察到典型的灰白色毛茸茸的生长物。在热那亚品种的叶片上生长最为旺盛。患病植株也出现了过早落叶的情况。根据Thines等人（4）建议的形态学研究，该真菌被鉴定为佩罗霉属（Peronospora belbahrii Thines）。孢囊梗无色，有一个长而直的主干，单轴分枝5至7次，长度为416至784μm（平均572μm）。孢囊梗末端有两个略微弯曲的锐尖小枝，较长的一个长12.5至25.0μm（平均17.1μm），较短的一个长5.0至18.μm（平均9.5μm）。较长与较短小枝的比例为0.7至3.0，平均比例为1.9。孢子囊呈圆形或略呈卵形，橄榄色至深褐色，大小为29.3×25.6（23.8至35.0×20.0至31.3μm）。长宽比为1.2（1.0至1.4）。对两个分离株进行了分子研究。从孢囊梗中提取DNA，然后使用ITS5和ITS4引物进行PCR。获得的序列（GenBank登录号HQ702191）与从甜罗勒中分离的佩罗霉属（Peronospora belbahrii）（例如登录号FJ394335和HN462241）以及佩罗霉属（Peronospora sp.）（例如登录号AY884605、AY919301和FJ346561）的序列显示出99.8%至100.0%的相似性。在欧洲，意大利（2）、法国（3）、德国（4）和瑞士（1）都报道过这种病害。据我们所知，这是匈牙利首次关于甜罗勒霜霉病的报道。参考文献：（1）L. Belbahri等人，《真菌学研究》109:1276，2005年。（2）A. Garibaldi等人，《植物病害》88:312，2004年。（3）A. Garibaldi等人，《植物病害》89:683，2005年。（4）M. Thines等人，《真菌学研究》113:532，2009年。
