Chuang M F, Ni H F, Yang H R, Shu S L, Lai S Y, Jiang Y L
Department of Plant Protection, Chiayi Agricultural Experiment Branch, Agricultural Research Institute, Chiayi, Taiwan.
Department of Horticulture, National Taiwan University, Taipei, Taiwan, R.O.C.
Plant Dis. 2012 Jun;96(6):906. doi: 10.1094/PDIS-08-11-0689-PDN.
Pitaya (Hylocereus undatus and H. polyrhizus Britt. & Rose), a perennial succulent plant grown in the tropics, is becoming an emerging and important fruit plant in Taiwan. In September of 2009 and 2010, a number of pitaya plants were found to have a distinctive canker on stems. The disease expanded quickly to most commercial planting areas in Taiwan (e.g., Pintung, Chiayi, and Chunghua). Symptoms on the stem were small, circular, sunken, orange spots that developed into cankers. Pycnidia were erumpent from the surface of the cankers and the stems subsequently rotted. After surface disinfestation with 0.1% sodium hypochloride, tissues adjacent to cankers were placed on acidified potato dextrose agar (PDA) and incubated at room temperature for 1 week, after which colonies with dark gray-to-black aerial mycelium grew. Hyphae were branched, septate, and brown and disarticulated into 0- to 1-septate arthrospores. Sporulation was induced by culturing on sterile horsetail tree (Casuarina equisetifolia) leaves. Conidia (12.79 ± 0.72 × 5.14 ± 0.30 μm) from pycnidia were one-celled, hyaline, and ovate. The internal transcribed spacer (ITS) region of ribosomal DNA was PCR amplified with primers ITS1 and ITS4 (2) and sequenced. The sequence (GenBank Accession No. HQ439174) showed 99% identity to Neoscytalidium dimidiatum (Penz.) Crous & Slippers (GenBank Accession No. GQ330903). On the basis of morphology and nucleotide-sequence identity, the isolates were identified as N. dimidiatum (1). Pathogenicity tests were conducted in two replicates by inoculating six surface-sterilized detached stems of pitaya with either mycelium or conidia. Mycelial plugs from 2-day-old cultures (incubated at 25°C under near UV) were inoculated to the detached stems after wounding with a sterile needle. Conidial suspensions (10 conidia/ml in 200 μl) were inoculated to nonwounded stems. Noninoculated controls were treated with sterile medium or water. Stems were then incubated in a plastic box at 100% relative humidity and darkness at 30°C for 2 days. The symptoms described above were observed on inoculated stems at 6 to 14 days postinoculation, whereas control stems did not develop any symptoms. N. dimidiatum was reisolated from symptomatic tissues. To our knowledge, this is the first report of N. dimidiatum causing stem canker of pitaya. References: (1) P. W. Crous et al. Stud. Mycol. 55:235, 2006. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, New York, 1990.
火龙果（Hylocereus undatus和H. polyrhizus Britt. & Rose）是一种生长在热带地区的多年生肉质植物，正成为台湾一种新兴且重要的水果作物。2009年9月和2010年，发现一些火龙果植株的茎上出现了一种独特的溃疡病。该病迅速蔓延至台湾的大多数商业种植区（如屏东、嘉义及彰化）。茎上的症状表现为小的、圆形、凹陷的橙色斑点，这些斑点会发展成溃疡。分生孢子器从溃疡表面突破外露，随后茎部腐烂。用0.1%次氯酸钠进行表面消毒后，将溃疡附近的组织置于酸化马铃薯葡萄糖琼脂（PDA）上，在室温下培养1周，之后长出带有深灰色至黑色气生菌丝的菌落。菌丝分枝、有隔膜且呈褐色，并断裂成0至1个隔膜的节孢子。通过在无菌木麻黄（Casuarina equisetifolia）叶片上培养诱导产孢。来自分生孢子器的分生孢子（12.79 ± 0.72 × 5.14 ± 0.30 μm）单细胞、透明且呈卵形。用引物ITS1和ITS4对核糖体DNA的内部转录间隔区（ITS）进行PCR扩增并测序。该序列（GenBank登录号HQ439174）与半知新壳梭孢（Neoscytalidium dimidiatum (Penz.) Crous & Slippers，GenBank登录号GQ330903）有99%的同源性。基于形态学和核苷酸序列同源性，这些分离物被鉴定为半知新壳梭孢（1）。通过用菌丝体或分生孢子接种6个表面消毒的离体火龙果茎进行致病性测试，重复两次。用无菌针划伤后，将来自2日龄培养物（在25°C近紫外光下培养）的菌丝块接种到离体茎上。将分生孢子悬浮液（200 μl中含10个分生孢子/ml）接种到未划伤的茎上。未接种的对照用无菌培养基或水处理。然后将茎置于塑料盒中，在30°C、100%相对湿度和黑暗条件下培养2天。接种后6至14天，在接种的茎上观察到上述症状，而对照茎未出现任何症状。从有症状的组织中再次分离出半知新壳梭孢。据我们所知，这是关于半知新壳梭孢引起火龙果茎溃疡病的首次报道。参考文献：（1）P. W. Crous等人，《Stud. Mycol.》55:235，2006年。（2）T. J. White等人，载于《PCR Protocols: A Guide to Methods and Applications》，M. A. Innis等人编，学术出版社，纽约，1990年，第315页。
