Department of Plant Pathology, National Chung Hsing University, Taichung 40227, Taiwan.
Department of Biotechnology, Asia University, Wufeng, Taichung 41354, Taiwan.
Plant Dis. 2018 Mar;102(3):600-607. doi: 10.1094/PDIS-05-17-0728-RE. Epub 2018 Jan 17.
The whitefly-transmitted tomato chlorosis virus (ToCV) belonging to the genus Crinivirus (family Closteroviridae) affects tomato production worldwide. ToCV was first recorded in Taiwan in 1998 affecting tomato production. In this study, a local virus isolate XS was obtained, after serial whitefly transmissions from a diseased tomato plant displaying general chlorosis were collected in central Taiwan. The whole genome sequence of XS was determined from cDNA fragments amplified by reverse transcription (RT)-PCR, first using the degenerate primers for viruses of Closteroviridae and followed by degenerate and specific primers designed on available sequences of the ToCV isolates. The nucleotide (nt) sequences of RNA-1 and RNA-2 of the XS shared low identities of 77.8 to 78% and 78 to 78.1%, respectively, with genome segments of other ToCV isolates. Nevertheless, the viral RNA-dependent RNA polymerase (RdRp), heat shock protein 70 homolog (Hsp70h), and major capsid protein (CP) shared 88.3 to 96.2% amino acid (aa) identities with other ToCV isolates, indicating that XS is a new strain of this virus. Phylogenetic analyses of these three proteins indicated that all ToCV isolates from different counties outside Taiwan are closely related and clustered in the same clade, whereas the XS isolate is distinct and forms a unique branch. A one tube RT-PCR assay using primers designed from the genomic sequence of the XS was able to detect the ToCV-XS in infected tomato plants and in individual whiteflies. A field survey during 2013 to 2016 revealed a high ToCV-XS prevalence of 60.5% in 172 tested tomato samples, demonstrating that ToCV-XS is becoming an emerging threat for tomato production in Taiwan.
烟粉虱传播的番茄褪绿病毒（ToCV）属于呼肠孤病毒科（Closteroviridae 科），影响全球的番茄生产。ToCV 于 1998 年在台湾首次记录，影响番茄生产。在这项研究中，从台湾中部一株表现普遍褪绿的病番茄植株上连续传代烟粉虱后，获得了一个当地病毒分离株 XS。使用 RT-PCR 从 cDNA 片段扩增的简并引物首次测定了 XS 的全基因组序列，然后使用 Closteroviridae 病毒的简并引物和基于已发表的 ToCV 分离物序列设计的简并和特异性引物。XS 的 RNA-1 和 RNA-2 的核苷酸（nt）序列与其他 ToCV 分离物的基因组片段分别具有 77.8%至 78%和 78%至 78.1%的低同一性。然而，病毒 RNA 依赖性 RNA 聚合酶（RdRp）、热休克蛋白 70 同源物（Hsp70h）和主要衣壳蛋白（CP）与其他 ToCV 分离物共享 88.3%至 96.2%的氨基酸（aa）同一性，表明 XS 是该病毒的一个新株系。这三种蛋白的系统进化分析表明，来自台湾以外不同国家的所有 ToCV 分离物密切相关，并聚类在同一分支中，而 XS 分离物则不同，形成一个独特的分支。使用从 XS 基因组序列设计的引物进行的单管 RT-PCR 检测能够在感染的番茄植株和单个烟粉虱中检测到 ToCV-XS。2013 年至 2016 年的田间调查显示，在 172 个测试的番茄样本中，ToCV-XS 的高流行率为 60.5%，表明 ToCV-XS 正在成为台湾番茄生产的一个新威胁。
