de Oliveira T S, Dallagnol L J, de Araujo Filho J V, de Castro Moretti F R, Camargo L E A
Faculdade de Agronomia Eliseu Maciel, Universidade Federal de Pelotas, Rio Grande do Sul, Brazil.
Escola Superior de Agricultura "Luiz de Queiroz," Universidade de São Paulo, São Paulo, Brazil.
Plant Dis. 2015 Jan;99(1):157. doi: 10.1094/PDIS-07-14-0693-PDN.
Platanus × acerifolia (Aiton) Willd. (London planetree) is a tree commonly used as an ornamental and in the furniture industry. In the summer of 2013, powdery mildew was observed on shoots of P. × acerifolia plants in the cities of Pelotas and Canela (State of Rio Grande do Sul, Brazil). Voucher specimens (n = 2) were deposited in the Phytopathological Museum Manoel Alves Oliveira at Federal University of Pelotas. Dense white powdery masses of conidia and mycelium were observed on leaves (abaxial and adaxial surfaces), petioles, and young stems. Leaves with high disease severities (≥70%) were deformed with curved edges to the adaxial side, and they often died. Mycelia were superficial with lobed appressoria. Conidiophores were straight, sometimes curved at the base, unbranched, cylindrical, 98 to 236 μm long (137.3 ± 41.2 μm) and composed of a cylindrical foot cell 49 to 102 μm long (66.9 ± 19.5 μm) and 4.4 to 6.4 μm wide (5.3 ± 0.8 μm) followed by two to four cells. Conidia were produced singly or in short chains (two to three), without distinct fibrosin bodies, ellipsoid to ovoid and measuring 24 to 37 μm long (29.5 ± 3.2 μm) and 12 to 19 μm wide (15.2 ± 1.4 μm), often with a wrinkled appearance. Primary conidia had truncate bases and rounded apex while both base and apex were truncated in secondary conidia. Germ tubes were produced apically (pseudoidium type). Chasmothecia were not observed. Genomic DNA was used to amplify the internal transcribed spacer (ITS) region using the ITS1 and ITS4 primers. The resulting sequence (602 bp) was deposited (Accession No. KF499270) in GenBank. BLASTn searches revealed similarity of 100 and 99% with Erysiphe platani from P. orientalis L. (Accession No. JQ365943.1) and P. occidentalis L. (Accession No. JX997805.1), respectively. Phylogenetic analysis placed our sequence in a clade (99% bootstrap support) which included only other E. plantani sequences. In short, morphological and molecular approaches allowed us to identify the infecting fungus as E. platani. For Koch's postulates, 10 detached leaves were inoculated (10 to 15 conidia cm) on their adaxial surface using an eyelash brush. Non-inoculated leaves served as control. All leaves were kept inside trays with petiole immersed in humidified cotton and maintained at 25 ± 1°C. Symptoms identical to those of the original leaves were observed 6 to 8 days after inoculation, whereas the control leaves remained symptomless. Although E. platani has been previously reported on P. × acerifolia in the city of Poços de Calda, state of Minas Gerais, Brazil (1) and on P. occidentalis in Korea (2), to our knowledge, this is the first record of E. platani on P. × acerifolia in Rio Grande do Sul, Brazil. References: (1) E. M. Inokuti et al. New Dis. Rep. 15:38, 2007. (2) Y. J. La and H. D. Shin. Plant Dis. 97:843, 2013.
二球悬铃木（Platanus × acerifolia (Aiton) Willd.）是一种常用于观赏和家具行业的树木。2013年夏天，在巴西南里奥格兰德州佩洛塔斯市和卡内拉市的二球悬铃木植株的嫩枝上发现了白粉病。凭证标本（n = 2）保存在佩洛塔斯联邦大学的植物病理学博物馆马诺埃尔·阿尔维斯·奥利维拉处。在叶片（正反面）、叶柄和幼茎上观察到密集的白色粉状分生孢子和菌丝团。病情严重程度较高（≥70%）的叶片边缘向正面弯曲变形，且常枯死。菌丝体生于表面，有叶状附着胞。分生孢子梗直立，有时基部弯曲，不分枝，圆柱形，长98至236μm（137.3±41.2μm），由一个长49至102μm（66.9±19.5μm）、宽4.4至6.4μm（5.3±0.8μm）的圆柱形基部细胞和随后的两至四个细胞组成。分生孢子单个产生或形成短链（两至三个），无明显纤维蛋白体，椭圆形至卵形，长24至37μm（29.5±3.2μm），宽12至19μm（15.2±1.4μm），通常外观有皱纹。初生分生孢子基部截形，顶端圆形，而次生分生孢子基部和顶端均截形。芽管从顶端产生（拟粉孢型）。未观察到闭囊壳。使用ITS1和ITS4引物扩增基因组DNA的内转录间隔区（ITS）。所得序列（602bp）已存入GenBank（登录号KF499270）。BLASTn搜索显示，该序列与来自悬铃木（Platanus orientalis L.）（登录号JQ365943.1）和美国梧桐（Platanus occidentalis L.）（登录号JX997805.1）的悬铃木白粉菌（Erysiphe platani）的相似性分别为100%和99%。系统发育分析将我们的序列置于一个分支中（自展支持率为99%），该分支仅包含其他悬铃木白粉菌序列。简而言之，形态学和分子方法使我们能够将感染的真菌鉴定为悬铃木白粉菌。为了进行柯赫氏法则验证，使用睫毛刷在10片离体叶片的正面接种（每平方厘米接种10至15个分生孢子）。未接种的叶片作为对照。所有叶片置于托盘中，叶柄浸在湿润的棉花中，保持在25±1°C。接种后6至8天观察到与原始叶片相同的症状，而对照叶片无症状。尽管此前在巴西米纳斯吉拉斯州波苏斯迪卡尔达市的二球悬铃木上（1）以及在韩国的美国梧桐上（2）已报道过悬铃木白粉菌，但据我们所知，这是巴西南里奥格兰德州二球悬铃木上首次记录到悬铃木白粉菌。参考文献：（1）E. M. Inokuti等人，《新病害报告》15:38，2007年。（2）Y. J. La和H. D. Shin，《植物病害》97:843，2013年。
