Garibaldi A, Bertetti 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):632. doi: 10.1094/PDIS-91-5-0632B.
Petunia × hybrida (Solanaceae) includes several hybrids that are grown as ornamental plants and are very much appreciated for their long-lasting flowering period. Among those, the variety pendula is often selected because of its hanging growth habit that is favorable for balcony decoration. During the summer of 2005, severe outbreaks of a previously unknown powdery mildew were observed on all petunia plants in several gardens near Biella and Torino (northern Italy). Both surfaces of the leaves of affected plants were covered with white, dense mycelia and conidia. As the disease progressed, infected leaves turned yellow and died. Mycelia also were observed on stems and flowers. Conidia were hyaline, ellipsoid, borne in short chains (with a maximum of four conidia per chain), and measured 27 to 36 × 17 to 21 μm (average 31 × 19 μm). Conidiophores, 130 to 154 μm (average 140 μm) long, showed the foot cell (measuring 42 to 65 × 10 to 12 μm, average 52 × 11 μm) followed by three shorter cells measuring 27 to 30 × 13 to 17 μm (average 29 to 14 μm). Fibrosin bodies were absent. Chasmothecia were not observed in the collected samples. The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 (3) and sequenced. BLASTn analysis (1) of the 588 bp obtained showed an E-value of 0.0 with Golovinomyces orontii (Erysiphe orontii) (2). The nucleotide sequence has been assigned GenBank Accession No. DQ 987491. Inoculations were made by gently pressing diseased leaves onto leaves of five healthy Petunia × hybrida var. pendula plants, belonging to cv. Surfinia. Five noninoculated plants served as controls. Inoculated and noninoculated plants were maintained in a greenhouse at temperatures between 14 and 30°C. After 10 days, typical powdery mildew symptoms 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 P. × hybrida caused by G. orontii in Italy. A powdery mildew of P. × hybrida reported in 1966 in Romania has been attributed to E. cichoracearum (4), while Braun (2) reported P. × hybrida as a possible host of E. orontii. 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) U. Braun. A Monograph of the Erysiphaceae (Powdery Mildews). Cramer, Berlin, GDR, 1987. (3) D. E. L. Cooke and J. M. Duncan. Mycol. Res. 101:667, 1997. (4) E. Eliade. Reprium nov. Spec. Regni veg.73:43, 1966.
矮牵牛（茄科）包含多个作为观赏植物种植的杂交品种，因其花期持久而备受喜爱。其中，垂吊矮牵牛品种常因其下垂的生长习性而被选用，这种习性有利于阳台装饰。2005年夏季，在意大利北部比耶拉和都灵附近的几个花园里，所有矮牵牛植株上都爆发了一种此前未知的白粉病。患病植株的叶片两面都覆盖着白色、致密的菌丝体和分生孢子。随着病情发展，受感染的叶片变黄并死亡。在茎和花上也观察到了菌丝体。分生孢子无色透明，椭圆形，呈短链状（每条链最多有四个分生孢子），大小为27至36×17至21μm（平均31×19μm）。分生孢子梗长130至154μm（平均140μm），基部细胞（大小为42至65×10至12μm，平均52×11μm）之后是三个较短的细胞，大小为27至30×13至17μm（平均29×14μm）。没有观察到纤维状小体。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588bp序列进行BLASTn分析，结果显示与奥氏白粉菌（白粉菌属）的E值为0.0。该核苷酸序列已被GenBank收录，登录号为DQ 987491。通过将病叶轻轻压在五株健康的垂吊矮牵牛（品种为“冲浪者”）植株的叶片上进行接种。五株未接种的植株作为对照。接种和未接种的植株在温度为14至30°C的温室中养护。10天后，接种的植株出现了典型的白粉病症状。未接种的植株没有出现症状。致病性测试进行了两次。据我们所知，这是意大利关于奥氏白粉菌引起矮牵牛白粉病的首次报道。1966年在罗马尼亚报道的矮牵牛白粉病被归因于菊科白粉菌，而布劳恩报道矮牵牛是奥氏白粉菌的可能寄主。该病的标本保存在意大利都灵大学的AGROINNOVA标本馆。参考文献：（1）S. F. 阿尔茨舒尔等人，《核酸研究》25:3389，1997年。（2）U. 布劳恩，《白粉菌科专论》，德国柏林克拉默出版社，1987年。（3）D. E. L. 库克和J. M. 邓肯，《真菌学研究》101:667，1997年。（4）E. 埃利亚德，《植物新种志》73:43，1966年。
