臺灣木瓜病毒病害感染現況與木瓜輪點病毒系統之變遷

Abstract

木瓜輪點病毒 (papaya ringspot virus, PRSV) 為台灣木瓜最主要的病毒病害，然根據前人研究台灣木瓜也受到木瓜畸葉嵌紋病毒 (papaya leaf distortion mosaic virus, PLDMV) 以及木瓜捲葉病毒 (papaya leaf curl virus, PaLCV) 的影響。本研究主要針對台灣田間木瓜病毒病害以及木瓜輪點病毒系統之變異現況進行調查，進而探討台灣木瓜病毒現今的流變狀況。研究採集 2018-2020 年間台灣田間露天栽培之木瓜，共187個樣本，PRSV 仍為台灣木瓜病毒危害之最大宗，佔全部樣本之78.07%，PLDMV以 9.09% 次之，而 PaLCV 則目前只有在二個田區發現佔總樣本數的 1.07%。本研究也發現台灣 PRSV的系統也在朝向產生較嚴重病徵的畸型 (DF) 以及嚴重嵌紋壞疽 (SMN) 系統演化，且大部分樣本無法以現有的木瓜輪點病毒系統之專一性引子對偵測。將無法以系統專一性引子對進行偵測的樣本做序列分析，顯示各個分離株的 P1 核酸序列相似度介於 91.4 ~ 93.5% 之間，而 CP 核酸序列則介於87.5 ～ 96.6%。根據前人研究三系統的 P1序列差異度最高，然親緣樹狀關係圖顯示無法單以 P1 的核酸序列進行各個系統的分類依據。台灣各地區 PRSV 的變異以及演化無法依據地理位置進行歸類及推論。根據本次的調查結果顯示，台灣 PRSV 的基因序列變異與當初調查結果已有相當大的差異，因此未來需要針對 PRSV系統重新再做詳細的分子鑑別。

Papaya ringspot virus (PRSV) is the major virus disease that causes severe threat in the papaya industry of Taiwan. According to previous studies, the papaya industry of Taiwan is also affected by papaya leaf distortion mosaic virus (PLDMV) and papaya leaf curl virus (PaLCV). This study is dedicated to investigate the current virus diversity and the variation of PRSV strains in Taiwan by collecting totally 187 samples between 2018 to 2020 to further illustrate the ecology of viral diseases of papaya in Taiwan. The result shows that the main virus diseases that affect papaya industry in Taiwan is PRSV, accounting for 78.07%, followed by PLDMV that accounts for 9.09%. In addition, we also reveal that the variation of PRSV in Taiwan is evolving towards strains resulting more severe symptoms, including deformation strain (DF) and severe mottling and necrosis (SMN), and most of the strains couldn’t be detected by available PRSV strains’ specific primers. Sequencing analysis against the collected samples could not be classified into any known strain. Our result shows that the similarity of P1 nucleotides among different isolates is ranged from 91.4% to 93.5%, whereas the similarity of CP nucleotides is from 87.5% to 96.6%. According to previous studies, the sequence in PRSV-P1 is the most diverse, but the strains cannot be differentiated by only P1 region in the phylogeny tree analysis. Besides, the variation of PRSV in Taiwan cannot be grouped according to geographical distribution. The results showed the variation of PRSV in Taiwan has undergone drastically changed compared to previous observations. Thus, more thorough molecular identification of PRSV is required.