木瓜輪點病募株系之不穩定性與其在不同日夜溫下對木瓜品種間的影響

Instability of Papaya Ringspot Virus Isolates and Their Effects on Papaya Cultivars under Different Day/Night Temperatures

木瓜輪點病（papaya ringspot disease）是木瓜生產最嚴重的限制因子，株齡半年以上而自然感染的｀臺農二號＇木瓜植株以嚴重黃化嵌紋型（SM）佔約70%,其次是嚴重壞疽黃化嵌紋型（SMN）與輕微黃化嵌紋型（M）•然甚少發現有嚴重畸型（DF）的病徵型木瓜株。木瓜植株罹患病毒後，因株齡大小而發病時間不同，株齡愈大，潛伏期愈長，病徵顯現較晚；田間自幼自然感染病毒的木瓜，其病徵型較儼重於網室栽培者。｀日陞＇接種單斑分離之病毒，其病徵型會因季節交替｀溫度變化而有不穩定表現，如嚴重壞疽黃化嵌紋型（SMN）木瓜病葉樣本分離的單株遇低溫出現畸形葉。在30/2S'C日夜溫下，接種M型的還濃五號＇於12天內其ELISA值低於接種嚴重畸型（DF）者，接種DF型的＇臺農五號＇其病徵表現極為嚴重，幾近萎凋或死亡·接種DF或SM型的日陞＇，在20/1S'C下於26天後萎凋或死亡，病毒表現與溫度具交感作用。因此，木瓜輪點病抗病育種應考逞進行篩選的環境與接種病毒的類型。

Papaya ringspot disease is a limiting factor of the papaya industry worldwide. Symptoms of infected papaya plants are varied. Survey was done on naturally infected papaya orchards. More than 70% of symptoms were classified as severe mottle (SM); severe mottle with necrosis (SMN) or mild mottle (M) symptoms were also frequently found in papaya orchards. The symptom severity was dependent upon the age of plants, the older plants showed less symptoms. Symptoms of the papaya plants infected earlier in the field without protection were more severe than symptoms of papaya cultivated under netting. Symptoms on '.'Sunrise''papaya plant after inoculation of papaya ringspot virus isolates under greenhouse conditions was through the year. The deformation symptom was found in the plants infected with the SMN virus isolate. The ELISA values of 'Tainung No. 5' infected with M isolate was significantly less than values of papaya plants infected with OF isolate at 30/25'(. The symptom of papaya plants infection of the OF islate was more severe than the other·isolates especially _in _the susceptible 'Sunrise'. The 'Sunrise' plants infected with the OF or SM virus isolates were wilted or dead in the 20/l 5°Cday/night temperature. The symptom of''Tainung No. 5'_ was more severe under the conditions of 30/25°(day/night temperature. Thus, the virus isolate and the conditions of the screening environment should be considered in the breeding program of papaya resistance to papaya ringspot virus.