Eni A O, Kumar P Lava, Asiedu R, Alabi O J, Naidu R A, Hughes Jd'A, Rey M E C
International Institute of Tropical Agriculture (IITA), Ibadan - PMB 5320, Nigeria.
Department of Plant Pathology, Washington State University, Irrigated Agriculture Research and Extension Center, Prosser.
Plant Dis. 2008 May;92(5):833. doi: 10.1094/PDIS-92-5-0833B.
Yam (Dioscorea spp., family Dioscoreaceae) is one of the most important food crops cultivated in the West African yam zone comprising the forest and savannah areas of Nigeria, Ghana, Côte d'Ivoire, Republic of Benin, and Togo, which account for more than 90% of the 4.59 million ha of yam cultivation worldwide (1). A survey was conducted in 2005 to document viruses in yams in Ghana, Togo, and the Republic of Benin. Samples (1,405) from five species of yam showing mosaic, chlorosis, and stunting as well as asymptomatic plants were tested for Dioscorea bacilliform virus (DBV, genus Badnavirus), Yam mosaic virus (YMV, genus Potyvirus), and Yam mild mosaic virus (YMMV, genus Potyvirus), the three most common viruses infecting yams. In addition, samples were tested for Cucumber mosaic virus (CMV), since CMV was previously reported to infect yams in Côte d'Ivoire (2) and Nigeria (3). In protein-A sandwich-ELISA with polyclonal antibodies to a cowpea isolate of CMV, 23 of the 1,405 samples (6 of 218 samples from Togo, 13 of 628 samples from Ghana, and 4 of 559 samples from Republic of Benin) tested positive for CMV. The CMV-positive samples were from D. alata (N = 16) and D. rotundata (N = 7), whereas all samples from D. cayenensis, D. dumetorum, and D. bulbifera tested negative. CMV was detected as mixed infections with DBV, YMV, or YMMV in 21 of 23 samples. Some of these samples showed puckering, chlorosis, mottling, and crinkling, whereas some plants infected by two or more viruses were asymptomatic. Only two samples from D. rotundata had a single infection of CMV and they showed mild chlorotic symptoms in young leaves that were inconspicuous in mature leaves. In sap inoculations, the virus induced systemic mosaic in Nicotiana glutinosa. The presence of CMV in ELISA-positive yam samples was further confirmed by immunocapture-reverse transcription (IC-RT)-PCR using CMV antibodies as trapping antibody and oligonucleotide primers specific for a 485 nt corresponding to 3' end of the coat protein gene and C-terminal noncoding region of RNA-3 (4). To confirm the specificity of IC-RT-PCR, the 485-bp amplicons from an isolate from the Republic of Benin was cloned into pCR2.1 (Invitrogen, Carlsbad, CA) and three independent clones were sequenced from both orientations. Pairwise comparison of a consensus sequence (Accession No. EU274471) with corresponding sequences of other CMV isolates deposited in GenBank showed 99% identity at the nucleotide sequence level (Accession No. U22821) and revealed that the CMV isolate from yam belongs to sub-Group IA. To our knowledge, this is the first report of CMV infection in yams (D. alata and D. rotundata) in Ghana, Togo, and the Republic of Benin. Together with a previous documentation of CMV in D. alata and D. trifida in Côte d'Ivoire and Nigeria (2,3), this report adds to existing knowledge on distribution of CMV in yams with implications for yam production and germplasm distribution in the West Africa Region. References: (1) FAO. Online publication. FAOSTAT, 2007. (2) C. Fauquet and J. C. Thouvenel. Plant Viral Diseases in the Ivory Coast. ORSTROM: Documentation Techniques. Paris, 1987. (3) Jd'A. Hughes et al. Phytopathology 87:S45, 1997. (4) S. Wylie et al. Aus. J. Agric. Res. 44:41, 1993.
山药（薯蓣属，薯蓣科）是在西非山药种植区种植的最重要的粮食作物之一，该种植区包括尼日利亚、加纳、科特迪瓦、贝宁共和国和多哥的森林和草原地区，这几个国家的山药种植面积占全球459万公顷山药种植面积的90%以上（1）。2005年开展了一项调查，以记录加纳、多哥和贝宁共和国山药中的病毒。对来自5种山药的1405份样本进行了检测，这些样本表现出花叶病、褪绿和发育不良症状，以及无症状植株，检测的病毒为薯蓣杆状病毒（DBV，杆状病毒属）、山药花叶病毒（YMV，马铃薯Y病毒属）和山药轻花叶病毒（YMMV，马铃薯Y病毒属），这三种是感染山药最常见的病毒。此外，还对样本进行了黄瓜花叶病毒（CMV）检测，因为此前有报道称CMV在科特迪瓦（2）和尼日利亚（3）感染山药。在使用针对CMV豇豆分离株的多克隆抗体进行的蛋白A夹心酶联免疫吸附测定（ELISA）中，1405份样本中的23份（来自多哥的218份样本中的6份、来自加纳的628份样本中的13份以及来自贝宁共和国的559份样本中的4份）CMV检测呈阳性。CMV阳性样本来自翼柄薯蓣（N = 16）和圆果薯蓣（N = 7），而来自黄肉薯蓣、参薯和 bulbifera 薯蓣的所有样本检测均为阴性。在23份样本中的21份中检测到CMV与DBV、YMV或YMMV混合感染。其中一些样本表现出起皱、褪绿、斑驳和皱缩症状，而一些感染两种或更多病毒的植株无症状。仅来自圆果薯蓣的两份样本为CMV单一感染，它们在幼叶中表现出轻微的褪绿症状，在成熟叶中不明显。在汁液接种试验中，该病毒在心叶烟中诱发系统花叶病。使用CMV抗体作为捕获抗体以及针对对应于外壳蛋白基因3'端和RNA - 3 C端非编码区的485 nt的寡核苷酸引物，通过免疫捕获 - 逆转录（IC - RT）-PCR进一步证实了ELISA阳性山药样本中存在CMV（4）。为了确认IC - RT - PCR的特异性，将来自贝宁共和国一个分离株的485 bp扩增子克隆到pCR2.1（Invitrogen，卡尔斯巴德，加利福尼亚州）中，并从两个方向对三个独立克隆进行测序。将一个共有序列（登录号EU274471）与GenBank中保存的其他CMV分离株的相应序列进行成对比较，结果显示在核苷酸序列水平上具有99%的同一性（登录号U22821），并表明来自山药的CMV分离株属于IA亚组。据我们所知，这是关于CMV在加纳、多哥和贝宁共和国山药（翼柄薯蓣和圆果薯蓣）中感染的首次报道。连同之前关于CMV在科特迪瓦和尼日利亚的翼柄薯蓣和 trifida 薯蓣中的记录（2,3），本报告增加了关于CMV在山药中分布的现有知识，对西非地区的山药生产和种质资源分布具有重要意义。参考文献：（1）粮农组织。在线出版物。FAOSTAT，2007年。（2）C. Fauquet和J. C. Thouvenel。《科特迪瓦的植物病毒病》。ORSTROM：文献技术。巴黎，1987年。（3）Jd'A. Hughes等人。《植物病理学》87：S45，1997年。（4）S. Wylie等人。《澳大利亚农业研究杂志》44：41，1993年。
