Garibaldi A, Bertetti D, Minerdi D, Gullino M L
Centre of Competence AGROINNOVA, University of Torino, Via Leonardo da Vinci 44, 10095 Grugliasco, Italy.
Plant Dis. 2007 May;91(5):635. doi: 10.1094/PDIS-91-5-0635B.
Lamium galeobdolon L. (Labiatae) is a common ornamental species that grows in shade areas and often used as a ground cover in gardens. During the summer of 2006, severe outbreaks of a previously unknown powdery mildew were observed on all Lamium spp. plants in some gardens near Biella (northern Italy). Both surfaces of the leaves of affected plants were covered with dense, white mycelia and conidia. As the disease progressed, infected leaves turned yellow and died. Mycelia and conidia also were observed on stems and flowers. Conidia were hyaline, ellipsoid, borne in short chains (with a maximum of five conidia per chain), and measured 29 to 37 × 16 to 20 μm (average 33 × 18 μm). Conidiophores, 91 to 104 μm (average 96 μm) long, showed the foot cell measuring 28 to 49 × 9 to 11 μm (average 38 × 10 μm), followed by three shorter cells measuring 14 to 26 × 9 to 15 μm (average 21 × 11 μm). Fibrosin bodies were absent. Chasmothecia were not observed in the collected samples. The internal transcribed spacer region (ITS) of rDNA was amplified using the primers ITS4/ITS6 (4) and sequenced. BLASTn analysis (1) of the 436 bp obtained showed an E-value of 0.0 with Golovinomyces orontii (Erysiphe orontii.) (3). The nucleotide sequence has been assigned GenBank Accession No. EF 121871. Inoculations were made by gently pressing diseased leaves onto leaves of five healthy L. galeobdolon plants. Five noninoculated plants served as controls. Inoculated and noninoculated plants were maintained in a greenhouse at temperatures between 15 and 28°C. After 10 days, typical powdery mildew colonies developed on inoculated plants. Noninoculated plants did not show symptoms. The pathogenicity test was carried out twice. To our knowledge, this is the first report of the presence of powdery mildew on L. galeobdolon caused by G. orontii in Italy. Blumer (2) was able to reproduce powdery mildew symptoms on L. galeobdolon using populations from cucumber, while Braun (3) reported L. galeobdolon as a possible host of E. orontii. Herbarium specimens of this disease are available at AGROINNOVA Collection, University of Torino, Italy. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) S. Blumer. Ber. Schweiz. Bot. Ges. 62:384, 1952. (3) U. Braun. A Monograph of the Erysiphaceae (Powdery Mildews). Cramer, Berlin, GDR, 1987. (4) D. E. L. Cooke and J. M. Duncan. Mycol. Res. 101:667, 1997.
野芝麻（唇形科）是一种常见的观赏植物，生长在阴凉处，常用于花园地被植物。2006年夏季，在意大利北部比耶拉附近的一些花园里，所有野芝麻属植物上都出现了一种前所未知的白粉病严重爆发情况。受感染植株的叶片两面都覆盖着密集的白色菌丝体和分生孢子。随着病情发展，受感染叶片变黄并死亡。在茎和花上也观察到了菌丝体和分生孢子。分生孢子无色透明，椭圆形，成短链状着生（每条链最多有5个分生孢子）, 大小为29至37×16至20μm（平均33×18μm）。分生孢子梗长91至104μm（平均96μm），基部细胞大小为28至49×9至11μm（平均38×10μm），后面接着3个较短的细胞，大小为14至26×9至15μm（平均21×11μm）。无纤维状小体。在所采集的样本中未观察到闭囊壳。使用引物ITS⁴/ITS⁶扩增核糖体DNA的内转录间隔区（ITS）并进行测序。对获得的436bp进行BLASTn分析显示，与奥氏高氏白粉菌（白粉菌属奥氏白粉菌）的E值为0.0。该核苷酸序列已被赋予GenBank登录号EF121871。通过将病叶轻轻压在5株健康的野芝麻植株叶片上进行接种。5株未接种的植株作为对照。接种和未接种的植株置于温度为15至28°C的温室中。10天后，接种植株上出现了典型的白粉病菌落。未接种植株未出现症状。致病性试验进行了两次。据我们所知，这是意大利首次报道奥氏高氏白粉菌引起的野芝麻白粉病。布卢默曾利用黄瓜上的菌源在野芝麻上再现了白粉病症状，而布劳恩报道野芝麻是奥氏白粉菌的可能寄主。意大利都灵大学AGROINNOVA标本馆有这种病害的标本。参考文献：（1）S.F.阿尔茨舒尔等人，《核酸研究》，25:3389，1997年。（2）S.布卢默，《瑞士植物学会学报》，62:384，1952年。（3）U.布劳恩，《白粉菌科（白粉病）专论》，克莱默出版社，东柏林，民主德国，1987年。（4）D.E.L.库克和J.M.邓肯，《真菌学研究》，101:667，1997年。
