木瓜畸葉嵌紋病毒與木瓜輪點病毒畸型系統的感染性選殖株轉錄病毒RNA在不同木瓜品種之交互感染研究

Abstract

台灣木瓜產業最大的限制因子為木瓜輪點病毒（Papaya ringspot virus，PRSV），而近年來發現另一木瓜病毒—木瓜畸葉嵌紋病毒（Papaya leaf distortion mosaic virus，PLDMV），不論是病徵、病害生態、分類地位、傳播媒介等，皆與木瓜輪點病毒之畸型系統（PRSV-DF）極為相似，因此被認為極有潛力成為台灣木瓜產業新的限制因子，需要進一步研究。本研究擬藉由先前已建構完成的PLDMV及PRSV-DF感染性選殖株來獲得胞外轉錄的純系病毒RNAs，探討兩病毒在不同木瓜品種上的病理性差異，以及二者在木瓜寄主體內的交互作用關係。本研究以同步、非同步接種兩病毒於不同木瓜品種上，觀察病徵及記錄病徵分級並以即時定量反轉錄聚合酶連鎖反應（Real-time RT-PCR）偵測兩病毒增幅動態，藉以解明兩病毒間的競合關係。病徵嚴重度方面，單獨感染PLDMV或是PRSV-DF在台農二號（TN2）木瓜上均與複合感染相差不大，但是單獨接種PLDMV與非同步接種（先接種PLDMV）的處理組，其病害發展較其他三處理組稍慢。而在紅妃（RL）木瓜上單獨感染PRSV-DF的病徵嚴重度最低，單獨感染PLDMV與複合感染也無明顯差異。在病毒增殖動態中，不論是TN2或RL上兩病毒量主要約在107至108 copy number之間，整體而言，PRSV-DF病毒量高於PLDMV。非同步接種時，後接種之病毒不影響先接種之病毒的增殖情況；同步接種時，兩病毒增殖也不互相干擾。此結果顯示兩病毒之間並無協力作用，兩者可以共存於田間，且以PRSV-DF較為優勢。未來若只專注於對木瓜輪點病的耐抗性，PLDMV將會帶來巨大的挑戰。

Papaya ring spot disease caused by Papaya ringspot virus (PRSV) is a main limiting factor for the papaya industry in Taiwan. Papaya leaf distortion mosaic virus (PLDMV) is a newly emerged virus of papaya. The pathological characteristics of PLDMV such as symptoms, transmission and ecological niche are similar to those of PRSV-deformation strain (PRSV-DF). Therefore, PLDMV is considered to be a potential threat for papaya industry. This study is dedicated to investigate the pathological differences in different papaya cultivars and the interaction in the hosts between PLDMV and PRSV-DF by the transfection using artificial viral RNA transcripts generated in vitro from the PLDMV and PRSV-DF infectious clones constructed in lab previously. The simultaneous and asynchronous inoculation tests in different papaya cultivars are conducted in this study to understand various statuses of co-infection. The results of area under disease progress curve (AUDPC) and dynamic of virus multiplication monitored by the real-time RT-PCR assays will be used to evaluate the interaction between PLDMV and PRSV-DF. Although the symptoms of the TN2 papaya could not be made a distinction between simultaneous infection and single infection of PLDMV or PRSV-DF, the results demonstrated that the symptom progression of PLDMV single inoculation and asynchronous inoculation (PLDMV previous) was slightly slower than other treatments. The symptom severity of PRSV-DF single infected RL papaya was the mildest one among all treatments. Furthermore, there were no significant differences between PLDMV single infection and mix infection in the RL papaya. Both in the TN2 and RL papaya, the amount of PLDMV and PRSV-DF was 107 to 108 copy numbers and PRSV-DF was more than PLDMV generally. The asynchronous tests presented that the later invasive virus did not affect the replication of previous virus. These findings suggest that there is no synergistic interaction of PLDMV with PRSV-DF. It seemed that these two viruses could exist independently in the field and PRSV-DF was more predominant. PLDMV may take big challenges when only focusing on the resistance to PRSV-DF in future.