菸草粉蝨 B 與 Q 生物小種傳播兩種番茄捲葉病毒之傳播生物學

Abstract

菸草粉蝨 (Bemisai tabaci) 傳播之番茄黃化捲葉病 (tomato yellow leaf curl disease) 經常造成田間番茄產量 100% 的損失。番茄黃化捲葉病是係以一群親緣關係相近之番茄黃化捲葉病毒種群 (tomato yellow leaf curl viruses) 所引發的植物病毒病害。番茄黃化捲葉病毒種群，屬於雙生病毒科 (Geminiviridae)、豆類金黃嵌紋病毒屬 (Begomovirus)。菸草粉蝨被認為是複合種，目前包含至少 28 種生物小種。在眾多生物小種中，B 型和 Q 型生物小種於全球分佈 (包括台灣) 且危害嚴重。雖然番茄黃化捲葉病毒的傳播特性已被研究許多，但其傳播模式仍存在著爭議。本研究的目的有三：一為比較兩種在台灣盛行的番茄黃化捲葉泰國病毒 (Tomato yellow leaf curl Thailand virus, TYLCTHV) 與番茄捲葉台灣病毒 (Tomato leaf curl Taiwan virus, ToLCTWV) 的傳播特徵；二為研究此兩種病毒是否會以經卵傳播 (transovarial transmission) 的方式傳播至病媒昆蟲的子代；三為檢測此兩種病毒於菸草粉蝨體內的感染及散播情形。藉由傳播試驗以及免疫螢光檢測結果，我們推測 菸草粉蝨 B 型生物小種以特殊且類似於持續性增殖型的模式傳播TYLCTHV，前人研究也顯示番茄捲葉病毒以色列分離株 Tomato yellow leaf curl virus Israel isolate (TYLCV-Is) 的傳播模式和 TYLCTHV 相似。傳播病媒傳播的結果顯示無論是菸草粉蝨 B 型還是 Q 型生物小種，皆可經由 1 至 2 小時的獲毒停留時間 (acquisition access period)，即可傳播 TYLCTHV 和 ToLCTWV 至供試番茄植株上。B 型生物小種的傳播效率比 Q 型生物小種更佳。B 型生物小種經由 2 至 6 小時的接種停留時間 (inoculation access period) 傳播 TYLCTHV 和 ToLCTWV；Q 型生物小種皆經由 2 小時的接種停留時間可傳播此兩種病毒，但其傳播效率皆低於B 型生物小種。此外，TYLCTHV 和 ToLCTWV 經由 B 型生物小種傳播的潛伏期 (latent period) 為 4 至 8 小時；TYLCTHV 和 ToLCTWV 於 Q型生物小種的潛伏期則分別為 10 和 40 小時。此兩種病毒皆可以持續保留在 B 型和 Q 型生物小種體內，但僅B 型生物小種保有傳播病毒的能力。有趣的是，僅僅 TYLCTHV 可以經由 B 型生物小種以經卵傳播的方式傳播給病媒昆蟲的子代。以上結果顯示，B 型生物小種為 TYLCTHV 效率較佳的病媒昆蟲。這個研究成果或許對田間 ToLCTWV 於短時間內被 TYLCTHV 取代的現象提出一些可能的原因。本研究更檢測了TYLCTHV 和 ToLCTWV 於B 型和 Q 型生物小種的感染狀況及散播情形，結果發現此兩種病毒皆可感染兩種菸草粉蝨生物小種的消化道，但僅有 B 型生物小種的微卵管被偵測到明顯的病毒抗原訊號，證實兩種病毒的散播途徑可至微卵管。本研究提供往後豆類金黃嵌紋病毒與菸草粉蝨間的傳播生物學研究的架構，從研究成果獲得的知識和資訊更可增進番茄黃化捲葉病的防治策略。

Whitefly-transmitted tomato yellow leaf curl disease (TYLCD) usually causes tomato yield losses of up to 100 % in tomato production. TYLCD is associated with a group of phylogenetically related viruses named tomato yellow leaf curl viruses (TYLCVs). These viruses belong to the genus Begomovirus, family Geminiviridae and are transmitted by B. tabaci which is also a species complex with at least 28 biotypes. Among these biotypes, B. tabaci B and Q biotypes are predominant biotypes and cause great economic losses globally including Taiwan. Even though the transmission of TYLCVs by B. tabaci have been studied by several research groups, the transmission mode of TYLCVs still remains controversial. The first objective of my study was to determine transmission characteristics for Tomato yellow leaf curl Thailand virus (TYLCTHV) and Tomato leaf curl Taiwan virus (ToLCTWV), which are predominant viruses in tomato fields in Taiwan, by B. tabaci B and Q biotypes. The second objective was to investigate whether TYLCTHV/ToLCTWV is transovarially transmitted to the progeny of its insect vectors. The third objective was to examine the infection and dissemination of either virus in its insect vectors. The transmission and indirect immunofluorescence assays concluded that TYLCTHV was transmitted by B. tabaci in special type of persistent-propagative transmission mode that Tomato yellow leaf curl virus Israel isolate (TYLCV-Is) also belongs to. The transmission of TYLCTHV and ToLCTWV by B. tabaci B and Q biotypes occurred with a minimum 1-2 h acquisition access period (AAP). Bemisia tabaci B biotype had better transmission ability than Q biotype for both viruses. Bemisia tabaci B biotype transmitted TYLCTHV and ToLCTWV with a minimum 2-6 h inoculation access period (IAP); Q biotype transmitted both viruses with a minimum 2-h IAP but showed lower efficiency than those transmitted by B biotype. In addition, B. tabaci B biotype transmitted TYLCTHV and TolCTWV with a latent period of no more than 4-8 h; Q biotype transmitted both viruses with a latent period of no more than 10 and 40 h, respectively. Even both viruses persisted in viruliferous B. tabaci B and Q biotypes for lifelong, but only B biotype remained the infectivity of TYLCTHV. Interestingly, transovarial transmission also only occurred in TYLCTHV transmitted by B. tabaci B biotype. These results imply that B. tabaci B biotype was a more efficient vector for TYLCTHV. It may attribute the displacement of ToLCTWV by TYLCTHV in the tomato fields in Taiwan within a few years to the virus-vector interaction. We further examined the infection and dissemination of TYLCTHV and ToLCTWV in B. tabaci B and Q biotypes. The results suggest that both viruses infected the alimentary gut of B. tabaci B and Q biotypes. Both viruses infected the ovariole of B. tabaci B biotype, but not Q biotype. This study would like to provide a framework for future studies on different begomovirus transmission by different biotypes of B. tabaci. The knowledge and information will improve the development of better management practices for TYLCD.