P系統木瓜輪點病毒之性狀

Characteristics of Papaya Ringspot Virus-type P

木瓜輪點病毒（papaya ringspot virus, PRSV）感染木瓜之系統稱為P系統（PRSV-P），嚴重危害熱帶及亞熱帶木瓜產業。P系統木瓜輪點病毒屬馬鈴薯Y病毒（potyvirus）群，正極性（positive sense）單股RNA為10326個核苷酸組成，轉譯或3344個胺基酸之聚蛋白，裂解為鞘蛋白及內含體（inclusion）等基因產物。五個病毒分離株之鞘蛋色基因有89.6%以上相同。P系銃木瓜輪點病毒在50～60℃間不活化，耐稀釋度為10-3之間，耐保存性一般為8～72小時之間，但亦有研究結果達11天之久。木瓜上病徵為葉片畸形或嵌紋，莖及葉柄上出現水浸狀條斑，果實上有輪斑，及植株矮化。在臺灣依病徵分類、P系統木瓜輪點毒素病可分為壞疽嵌紋型（SMN）、嚴重嵌紋型（SM）、輕微嵌紋型（M）、畸形重嵌紋型（SMD）及嚴重畸形型（DF）等。該病毒可經機械接種或蚜蟲非永續性傳播，不經種子傳病。本瓜輪點毒素病系統性感染木瓜（Carica papaya L.）及部份葫蘆科（Cucurbitaceae）植物，局部感染部扮藜科（Chenopodiaceae）植物。

Papaya strains of papaya ringspot virus (PRSV-P) causes a major disease problem on papaya cultivation in tropics and subtropics. PRSV-P is a member of potyviruses. The positive sense PRSV RNA is 10326 nucleotides in length and is translated into a polyprotein of 3344 amino acids. The coat protein regions of five sequenced PRSV strains shows more than 89.6% nucleotide identities. The thermal inactivation point of PRSV-P is 50~60°C within 10 minutes. Its dilution end point is at 10-3~10-5 and with longevity of 8 to 72 hours. It shows leaf deformation and mottles on papaya, water soaked steaks on leaf petioles and stem, and water soaked ringspot on fruit. Strains of PRSV-P from Taiwan include SMN, SM, M, SMD and DF. PRSV-P can be transmitted mechanically and through aphids in a non-persistent manner. Papaya seeds do not bear virus. Systemic hosts include Carica papaya L. and members of Cucurbitaceae. It causes local lesions on members of Chenopodiaceae.