| Abstract: | 甘藷褪綠矮化矮病毒 (sweet potato chlorotic stunt virus，SPCSV) 屬於Closteroviridae科Crinivirus屬，可經由粉蝨傳播，嚴重影響全世界甘藷的產量。根據基因體的系統演化樹分析，目前的SPCSV分離株可分為西非 (West African, WA) 和東非 (East African, EA) 兩個株系 (strain)。SPCSV始於2012年在台灣首次被報導，對於台灣SPCSV分離株之分子特徵至今仍了解甚少。本實驗室於2016年從嘉義市採集了具有褪綠的甘藷樣本，命名為CYI6。利用逆轉錄聚合酶鏈鎖反應 (reverse transcription-polymerase chain reaction, RT-PCR) 擴增cDNA片段進行CYI6的全基因組定序，先使用Closteroviridae科病毒簡併性引子對，再從SPCSV分離株的可用序列設計簡併性和專一性引子對進行擴增反應。CYI6的RNA1和RNA2核苷酸 (nucleotide, nt) 序列分別與WA strain 的SPCSV分離株具有98.7-98.9％和98.5-98.8％的高相同度 (identity)，但與EA strain相比，RNA1和RNA2的相同度僅為70.0-81.5％及70.3-70.5％。另外，根據系統演化樹分析，CYI6的RNA-dependent RNA polymerase (RdRp)，熱休克同源性蛋白70 (heat shock protein 70 homolog, Hsp70h) 和外鞘蛋白 (coat protein, CP) 與WA strain 的SPCSV分離株之胺基酸 (amino acid, aa) 相同度為96.4-99.8％，顯示CYI6是屬於WA strain的SPCSV分離株。使用CYI6專一性引子對進行RT-PCR檢測在田間具病徵的甘藷植株，於2016至2017年期間進行調查，結果顯示，自台北、台中、嘉義、台南、高雄及屏東等地區收集的108個甘藷樣本中，僅於嘉義市採集之樣本中檢測到SPCSV，檢出率為44.1％。由此可知，SPCSV在台灣的分佈仍受局限，要特別注意此病毒之散佈。
The whitefly-transmitted sweet potato chlorotic stunt virus (SPCSV), belonging to the genus Crinivirus of the family Closteroviridae, severely affects productions of sweet potatoes worldwide. The current SPCSV isolates can be divided into two strains, West African (WA) and East African (EA), according to the genomic phylogeny. SPCSV was reported in Taiwan since 2012, but the molecular characteristic of the local SPCSV isolates is poorly understood. In this study, the whole genome sequence of a virus isolate collected from Chiayi city in 2016, and denoted CYI6 was determined from cDNA fragments amplified by reverse transcription-polymerase chain reaction (RT-PCR), first using the degenerate primers for viruses of Closteroviridae and followed by degenerate and specific primers designed from available sequences of SPCSV isolates. The nucleotide (nt) sequences of RNA1 and RNA2 of the CYI6 shared high identities of 98.7-98.9% and 98.5-98.8%, respectively, with those of SPCSV isolates of the WA strain, but shared lower identities of 70.0-81.5% for RNA1 and 70.3-70.5% for RNA2 with those of the EA strain. Additionally, the RNA-dependent RNA polymerase (RdRp), heat shock protein 70 homolog (Hsp70h) and major coat protein (CP) of CYI6 shared 96.4-99.8% amino acid (aa) identities with those of SPCSV isolates of the WA strain as well as the phylogenetic results, indicating that CYI6 is a SPCSV isolate belonging to the WA strain. A one-step RT-PCR method using CYI6-specific primers was developed to detect SPCSV in symptomatic sweet potato plants in field. A total of 108 sweet potato samples were collected from areas of Taipei, Taichung, Chiayi, Tainan, Kaohsiung and Pingtung during 2016 to 2017 for field survey. A SPCSV detection rate of 44.1% was obtained from the samples collected from Chiayi City. Our result showed that the distribution of SPCSV is limited in Taiwan and its spread should be more concerned. |
