木瓜輪點病毒（SMN、DF系統）與木瓜畸葉嵌紋病毒在不同番木瓜品系上的交互作用

Abstract

於網室內進行病毒在葉片分佈試驗，接種2個星期將接種葉上方所有葉片以專一性引子對作RT-PCR偵測，顯示PRSV主要分佈在頂端幼葉，PLDMV在接種兩個星期後則測不出訊號，而葉序偵測結果顯示每週採樣方式以當週第7片葉片為最適合。在網室內以非同步的方式接種木瓜輪點病毒（PRSV）嚴重嵌紋壞疽系統（SMN）、嚴重畸形系統（DF）與木瓜畸葉嵌紋病毒（PLDMV），並分析不同接種方式對病徵與生長量的影響，調查葉片病徵曲線面積顯示接種PLDMV的病徵比PRSV要來的輕微，混接PLDMV處理的病徵比只有PRSV系統的病徵要輕微，先接種PLDMV後再接PRSV對降低病徵嚴重性最明顯，類似交叉保護的效果；接種時間間隔以接種PLDMV 4個星期後再接PRSV的保護效果最佳，於第2與第4星期重複接種PRSV會降低PLDMV的保護效果；改變DF系統與PLDMV的接種順序在病徵上的嚴重差異大於SMN系統，顯示DF與PLDMV在病徵病理性較相似。相對於PLDMV，PRSV在莖上會產生明顯的水浸斑，而各處理水浸斑在莖上的分佈曲線面積結果與葉部病徵類似；PLDMV在株高與莖粗相對生長率上仍具干擾PRSV的效果，但差異不明顯，節數絕對生長率則無差異。各處理的螢光變量比值（Fv/Fm）除對照組外，其於處理差異不大；以專一性引子對偵測顯示，PRSV兩系統的增殖速率大於PLDMV，SMN與DF系統在初期會相互干擾對方複製，後期則與PLDMV都可共存於寄主內。網室內同步接種處理則顯示PLDMV的干擾效果降低，各處理的差異不大，主要受PRSV的影響，顯示PRSV在同步接種的競爭優勢大於PLDMV，但三種病毒於後期仍可共存於寄主內。露天同步接種試驗各處理包含對照組的差異皆不明顯，於第8個星期做病毒檢測，發現各處理皆感染PRSV的DF系統，顯示DF系統為田間主要流行系統。‘台大選系10號’在本次試驗的耐病表現較商業種‘台農二號’優良，顯示未來在田間露天栽培環境下可避免PRSV與PLDMV對其造成的危害。 木瓜輪點病毒（PRSV）在台灣分化成數個系統，其中又以嚴重嵌紋壞疽系統（SMN）對番木瓜的破壞力最大，本試驗探討由台大園藝系所育成的耐病品系對木瓜輪點病毒SMN系統與未來可能流行的木瓜畸葉嵌紋病毒（PLDMV）的耐受度，並以商業品種 ‘台農2號’ 、 ‘日陞’ 與 ‘紅妃’ 品種做對照組。接種SMN 4星期後的葉片病徵以 ‘NTU04’ 與 ‘NTUB’ 的表現最佳，‘日陞’種則產生嚴重嵌紋病徵，重複接種SMN 12個星期後則以 ‘NTU04’ 與 ‘NTU11’ 表現最為優良，‘日陞’種則全部死亡。接種PLDMV 4星期後以‘台農2號’與‘日陞’種的葉片上會產生嵌紋病徵，其餘品種（系）的病徵則不明顯，重複接種PLDMV 12個星期後大部分品種（系）會產生主脈透化的現象，台大選系 ‘NTU08’ 與 ‘NTI10’ 的病徵較輕微， ‘台農2號’ 葉脈透化明顯，‘日陞’種則與接種SMN系統處理一樣全部死亡。各品種（系）接種SMN的葉片病徵明顯比接種PLDMV嚴重，顯示SMN系統的破壞力大於PLDMV，且接種SMN在莖上會形成明顯的水浸病斑，PLDMV則較輕微，本試驗顯示台大選系 ‘NTU04’與 ‘NTU08’ 的耐病性表現普遍較商業品種來的優良，而品種（系）接種SMN與PLDMV在各週的葉片病徵曲線發展面積具顯著相關，顯示品種（系）抗（耐）SMN的表現程度會同樣表現在抗（耐）PLDMV的反應上。

The one-step RT-PCR assay with strain-specific primers was detected of various PRSV strains and PLDMV on different phyllotaxy. The PRSV signals in young leaves were stronger than olds, and the PLDMV couldn’t be detected 2 weeks after inoculated. The results of phyllotaxy detections revealed that the proper phyllotaxy for virus detected every week were the 7th phyllotaxy. The leaves symptoms on asynchronous inoculation assay were mild when inoculated with PLDMV, especially inoculated with PLDMV first. The slight symptoms inducing by PLDMV were similar to cross-protection and the best precaution on the asynchronous inoculation were the 0、4 weeks interval. Repeated inoculations with PRSV in 2sec and 4th week after inoculating with PLDMV at fist week would cause sever symptoms. Change the orders of inoculation would make the severity of symptoms different, especially the turns in DF and PLDMV, indicating the interference between DF and PLDMV were more than SMN and PLDMV. The result of distribution rate of water spots produce by different inoculated treatment were similar to leaves symptoms. The interference caused by PLDMV on relative growth rate of plant height and steam width was less when inoculated with PRSV. Detected by RT-PCR assay revealed that SMN and DF strain would interfere in each others replications at the early stage, but the two strains of PRSV and PLDMV could be detected definitely 8 weeks after first inoculated. The influence induced by PLDMV was not significant in simultaneous inoculation test, indicating that when PLDMV and PRSV simultaneous infected papaya, PRSV were more competitively than PLDMV. Papayas were infected DF strain in simultaneous inoculation in natural field, revealing that DF strain would be the predominant strain in the field of Taiwan. The results in this inoculation test also revealed that hybrid line‘NTU10’showed the high tolerance to PRSV-SMN、PRSV-DF and PLDMV, even complex infected by two virus, and‘TN2’is a susceptible cultivar to PRSV and PLDMV. Papaya ringspot virus was divided into many strains, and severe mottling with necrosis strain（SMN）was the most destructive strain in Taiwan. This experiment evaluated the tolerance of the tolerant papaya line which were bred by Department of Horticulture, NTU and commercial papaya cultivar after inoculated with SMN strain and PLDMV which may be the popular virus in Taiwan in the future. The leaves symptom of hybrid line ‘NTU04’ and ‘NTUB’ showed minor symptoms than ‘Sunrise’ 4 weeks after inoculated with SMN strain. In 12 weeks after inoculated with SMN strain, there were minor symptoms in ‘NTU04’ and ‘NTU11’, but ‘Sunrise’ cultivar was completely wilted. Unlike other cultivar or line, ‘TN2’ and ‘Sunrise’ showed severe symptom on leaves 4 weeks after inoculated with PLDMV. Hybrid line ‘NTU08’ and ‘NTU10’ still showed minor symptom, ‘TN2’ showed severe mosaic symptom on leaves and ‘Sunrise’ cultivar completely wilted 12 weeks after inoculated with PLDMV. Compared the symptoms of SMN strain with PLDMV, revealing that SMN was more destructive than PLDMV, and SMN strain would cause the steam spotted. There were the significant correlation in AUDPC（area under disease progress curve）of SMN strain and PLDMV, indicating that the plant’s tolerant reactions in SMN strain were similar to PLDMV.