Wangai A W, Mandal B, Pappu H R, Kilonzo S
Kenya Agricultural Research Institute, P.O. Njoro, Kenya.
Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793.
Plant Dis. 2001 Oct;85(10):1123. doi: 10.1094/PDIS.2001.85.10.1123B.
Tomato spotted wilt virus (TSWV) of the genus Tospovirus, family Bunyaviridae (1), causes an economically important virus disease in tomato in several parts of the world. The virus has a wide host range that includes numerous crops and weeds and is transmitted by at least seven species of thrips. Tomato crops in the Subukia, Bahati, and Kabazi areas of the Nakuru District in Kenya were affected by a disease suggestive of TSWV infection during the November 1999 to March 2000 tomato-growing season. Farmers reported up to 80% losses of their potential yields. Characteristic symptoms were noticed on fruits, especially when they were green. Distinct concentric rings on fruits, which later turned into brown, uneven ripening, were the most visible symptoms. Foliage did not develop pronounced symptoms, but mild bronzing was observed in a few cultivars. However, foliage senesced prematurely, starting with older leaves. Foliar symptoms were mistaken for blight infection, and as a result, excessive fungicides were applied that failed to manage the disease. To test for TSWV infection, tomato leaf samples collected from the fields were tested initially with a TSWV test kit (HortiTech, Horticulture Research International, Wellesbourne, UK), and the results were confirmed by double-antibody sandwich-enzyme-linked immunosorbent assay with antibodies from Agdia Inc. (Elkhart, IN). Further molecular characterization was done using reverse transcription-polymerase chain reaction (RT-PCR). Total RNA was extracted from symptomatic leaves of tomato cv. Money Maker using the RNeasy mini kit (Qiagen Inc., Valencia, CA). Using primers 5' TTAAGC AAGTTCTGTGAG 3' and 5' ATGTCTAAGGTTAAGCTC 3' specific to the nucleoprotein (N) gene of TSWV, the N gene was amplified by RT-PCR (2). A 777-bp product of the expected size was obtained from symptomatic plants, whereas no amplification was obtained from noninfected tomato. The PCR product was cloned into pGEM-T Easy (Promega, Madison, WI) and sequenced. A search of GenBank revealed a sequence identity of 95 to 99% with the N genes of known TSWV isolates. To our knowledge, this is the first report TSWV infection of tomato in Kenya. Considering its wide host range, future surveys should be directed toward estimating its incidence in tomato and other TSWV-susceptible crops, such as Irish potatoes, pepper, peanut (groundnut), beans, and a wide variety of ornamental cut flowers in Kenya. References: (1) J. W. Moyer. Tospoviruses (Bunyaviridae). Pages 1803-1807 in: Encyclopedia of Virology. A. Granoff and R. G. Webster, eds. Academic Press, San Diego, CA, 1999. (2) Jain et al. Plant Dis. 82:900, 1998.
番茄斑萎病毒（TSWV）属于布尼亚病毒科番茄斑萎病毒属（1），在世界上多个地区的番茄上引发了一种具有经济重要性的病毒病。该病毒具有广泛的寄主范围，包括众多农作物和杂草，并由至少七种蓟马传播。在1999年11月至2000年3月的番茄种植季节，肯尼亚纳库鲁区苏布基亚、巴哈蒂和卡巴齐地区的番茄作物受到一种疑似TSWV感染的病害影响。农民报告称其潜在产量损失高达80%。在果实上观察到了特征性症状，尤其是当果实为绿色时。果实上明显的同心环，随后变为褐色、成熟不均，是最明显的症状。叶片未出现明显症状，但在少数品种中观察到轻度青铜色。然而，叶片过早衰老，从老叶开始。叶片症状被误认为是疫病感染，结果施用了过量的杀菌剂，但未能控制住病害。为检测TSWV感染，从田间采集的番茄叶片样本首先用TSWV检测试剂盒（HortiTech，园艺研究国际公司，英国韦尔斯伯恩）进行检测，结果通过使用来自Agdia公司（印第安纳州埃尔克哈特）的抗体进行双抗体夹心酶联免疫吸附测定得到确认。进一步的分子特征分析使用逆转录-聚合酶链反应（RT-PCR）进行。使用RNeasy迷你试剂盒（Qiagen公司，加利福尼亚州瓦伦西亚）从番茄品种“Money Maker”的有症状叶片中提取总RNA。使用针对TSWV核蛋白（N）基因的特异性引物5' TTAAGC AAGTTCTGTGAG 3'和5' ATGTCTAAGGTTAAGCTC 3'，通过RT-PCR扩增N基因（2）。从有症状的植株中获得了预期大小的777碱基对产物，而从未感染的番茄中未获得扩增产物。PCR产物被克隆到pGEM-T Easy（Promega公司，威斯康星州麦迪逊）中并进行测序。在GenBank中搜索发现与已知TSWV分离株的N基因序列同一性为95%至99%。据我们所知，这是肯尼亚番茄TSWV感染的首次报道。考虑到其广泛的寄主范围，未来的调查应针对估计其在肯尼亚番茄及其他TSWV易感作物，如爱尔兰马铃薯、辣椒、花生（落花生）、豆类以及多种观赏切花中的发病率。参考文献：（1）J. W. Moyer。番茄斑萎病毒属（布尼亚病毒科）。载于：《病毒学百科全书》。A. Granoff和R. G. Webster编。学术出版社，加利福尼亚州圣地亚哥，1999年，第1803 - 1807页。（2）Jain等人。植物病害。82:900，1998年。
