Dart N L, Weeda S M
Virginia Department of Agriculture and Consumer Services, Office of Plant Industry Services, Richmond 23226.
Virginia State University, Department of Agricultural Research, Petersburg 23806.
Plant Dis. 2011 Dec;95(12):1592. doi: 10.1094/PDIS-06-11-0474.
In October 2010, containerized Acer palmatum Thunb. trees ('Red Select', 'Viridis', and 'Hubb's Red Willow') with crown cankers and root rot were observed at a central Virginia nursery. Sections of lower stem cankers and rootlets were sampled from 14 trees by surface-sterilizing tissue and plating on V8 juice agar. A species of Cylindrocarpon was isolated from 72% of sampled trees and recovered from 57% of 50 cankers and 74% of 50 sections of symptomatic rootlets. On potato dextrose agar (PDA), macroconidia were cylindrical, straight, and rounded at both ends. Chlamydospores were common and intercalary or terminal in the mycelium. To identify to species, the internal transcribed spacer of ribosomal DNA and partial sequences of the beta tubulin gene were sequenced and compared with published sequences (GenBank Accession Nos. AM419110.1 and AM419109.1), which exactly matched sequences of Cylindrocarpon macrodidymum, a recently described species (1,2). Neighbor-joining analyses using Blast Tree View placed C. macrodidymum and the unknown isolate in a closely related but distinct clade from C. pauciseptatum and C. liriodendri. Species-specific primers also confirmed the isolates to be C. macrodidymum (2). A. palmatum seedlings (generic root stock) were inoculated by placing a colonized PDA plug over 1-cm scalpel incision wounds (n = 12) and wrapping treated sections of stem with Parafilm to prevent desiccation. Twelve root systems were inoculated by mixing a colonized PDA plate with 1 liter of water and drenching the soil of each plant. Twelve wounds and root systems were inoculated with uncolonized PDA for controls. After 4 weeks, inoculated wounded seedlings developed brown lesions extending 1 to 3 cm from incision wounds. Inoculated roots developed root rot. Controls produced no visible symptoms. A Cylindrocarpon sp. was recovered from 85% of surface-sterilized sections of inoculated wounded stem and 100% inoculated symptomatic roots. No Cylindrocarpon sp. was isolated from stem or root controls. To our knowledge, this is the first report of this pathogen on A. palmatum. Other reported hosts include grapevines (Vitis spp.) and apple (Malus spp.) (3). This finding demonstrates the ability of C. macrodidymum to impact an ornamental host and the potential for this pathogen to impact the ornamental nursery industry. References: (1) S. Alaniz et al. Plant Dis. 93:821, 2009. (2) J. Auger et al. Plant Dis. 91:470, 2007. (3) Y. T. Tewoldemedhin et al. Eur. J. Plant Pathol. 129:637, 2011.
2010年10月，在弗吉尼亚州中部的一家苗圃中，人们发现了带有树冠溃疡病和根腐病的容器栽培鸡爪槭（‘Red Select’、‘Viridis’和‘Hubb's Red Willow’品种）。通过对14棵树的下部茎溃疡病部位和细根进行表面消毒处理后取样，并接种到V8汁琼脂培养基上。从72%的取样树木中分离出了一种柱孢属真菌，在50个溃疡病样本中有57%分离到该菌，在50个有症状的细根样本中有74%分离到该菌。在马铃薯葡萄糖琼脂（PDA）培养基上，大型分生孢子呈圆柱形，直形，两端圆形。厚垣孢子常见，在菌丝体中呈间生或顶生。为了鉴定到种，对核糖体DNA的内部转录间隔区和β微管蛋白基因的部分序列进行测序，并与已发表的序列（GenBank登录号AM419110.1和AM419109.1）进行比较，结果与最近描述的一个种——大型双梗柱孢（Cylindrocarpon macrodidymum）的序列完全匹配（1,2）。使用Blast Tree View软件进行的邻接法分析将大型双梗柱孢和未知分离株置于一个与少隔柱孢（C. pauciseptatum）和鹅掌楸柱孢（C. liriodendri）密切相关但又不同的进化枝中。种特异性引物也证实这些分离株为大型双梗柱孢（2）。通过在1厘米长的手术刀切口伤口上放置一块已被该真菌定殖的PDA培养基块（n = 12），并用Parafilm包裹处理过的茎段以防止干燥，从而对鸡爪槭幼苗（普通砧木）进行接种。通过将一块已被该真菌定殖的PDA平板与1升水混合，并浇灌每株植物的土壤，对12个根系进行接种。12个伤口和根系接种未被定殖的PDA作为对照。4周后，接种的有伤口幼苗在切口伤口处出现褐色病斑，病斑从切口处延伸1至3厘米。接种的根系出现根腐病。对照没有出现可见症状。从85%的接种了有伤口茎段的表面消毒样本和100%接种了有症状根系的样本中分离到柱孢属真菌。在茎或根的对照样本中未分离到柱孢属真菌。据我们所知，这是该病原菌在鸡爪槭上的首次报道。其他报道的寄主包括葡萄（Vitis spp.）和苹果（Malus spp.）（3）。这一发现表明大型双梗柱孢有能力影响一种观赏寄主，并且这种病原菌有可能影响观赏苗圃产业。参考文献：（1）S. Alaniz等人，《植物病害》93:821，2009年。（2）J. Auger等人，《植物病害》91:470，2007年。（3）Y. T. Tewoldemedhin等人，《欧洲植物病理学杂志》129:637，2011年。
