抗輪點病毒(PRSV)基因轉殖木瓜對生態影響及環境安全之評估

Abstract

本報告報導國內首宗基因轉殖作物一抗點病毒(papay aringspot virus，PRSV)基因轉殖木瓜之生態安全性評估結果。基因轉殖木瓜四個株系(16-0-1、17-0-1、17-0-5及18-1-4)於1996~2003年間在台中縣霧峰農業試驗所隔離網室和隔離試驗田進行一系列的觀察試驗，並與栽植於相同環境中的非轉殖木瓜互相比餃，以分析該基因轉木瓜之栽植對於環境生態可能發生之影響。調查結果顯示，該基因轉殖木瓜與對照木瓜在田間所表現之一般園藝性狀、果實產量與品質具有差異，此乃由於對照木瓜不抗輪點病，於種植一段時間後即迅速發病，導致生育不良、果實品質差且產量低。評估結果為，該轉殖木瓜轉變雜草之可能性極低。由於該基因轉殖木瓜皆為雌株，因而所轉殖之基因不會經由花粉外流至其他木瓜；但將來所推廣之轉殖木瓜品種若含有兩性株和雄株，則有可能發生種內之基因流佈(gene flow)問題，因此需加以防範。對試驗田雜草進行取樣並以PCR分析，並未發現木瓜所含之轉殖基因有轉移到雜草之跡象。由網室內盆栽試驗之查結果得知，基因轉殖木瓜根圈附近土壤微生物如土壤總細菌、總真菌、固氮細菌，溶菌及蛋白分解菌等之密度、土壤線蟲的種類與族群消長於木瓜植株上棲息或取食之昆蟲、蟎類及其天敵之種類與族群等，與對照木瓜間均無顯著性差異，顯示其對生態環境中之生物相並無負面影響。田間觀察顯示，基因轉植木瓜具有抗輪點病毒之特性，輪點病之發生明顯於對照木瓜;但該轉殖木瓜對輪點病並非免疫，且源自同一轉殖株系的組培植株之間對於輪點病毒之抗性亦不一致，其程度從完全免疫到輕微感病，以至於中度感病等不同層次皆可發現。此外，本試驗結束後該隔離田區曾另外偅植轉殖木瓜及非轉殖一批，其中有部分植株(包括基因轉殖與非轉殖木瓜)出現木瓜畸葉嵌紋病毒(papaya leaf-distoration mosaic virus，PLDMV)病徵，因此推知基因轉殖木瓜自栽於田間起，便與周遭環境產生互動與影響，因而造成病毒間之族群消長；其互動與影響具有累積效果，最後遂導致次要病毒之崛起，此現象值得長期追蹤與進一步探討。 In this paper we report the results of environmental safety assessment of the first transgenic crop, i.e. transgenic papaya carrying the coat protein gene of Papaya ringspot virus (PRSV), in Taiwan. The assessment was performed under the condition of an isolated field, including open field and net house, at Agricultural Research Institute (ARI) during 1996 ~2003. The influence of transgenic papaya lines 16-0-1, 17-0-1, 17-0-5, and 18-14 on the ecological environment was compared with that of non-transgenic papaya. The results showed that the horticultural characteristics, fruit quality, and yield were different between transgenic and non-transgenic papayas planted in the open field. This was due to non-transgenic papaya become diseased with PRSV very soon after transplanted into the field, resulting in plant declining, poor fruit quality, and low yield. It was found that the possibility of the occurrence of volunteer papaya derived from this transgenic papaya is very low. The gene flow through the spread of transgenic pollen did not occur, since all the transgenic papaya are female trees and did not produce pollen. However, since its hybrid progenies will contain hermaphroditic or male, the intra-species gene flow may occur in the future if these hermaphroditic or male progenies are cultivated. It is perceived that some strategies need to be taken to prevent such kind of gene flow. The possibility of gene flow to some weedy grass species grown in and around the test field was also surveyed by PCR analysis with primers based on the transgene sequence. In net house, all the materials were planted in pots filled with man-made media and with well controlled irrigation and fertilization. The media of rhizosphere was carefully sampled periodically and analyzed for soil borne bacteria, fungi, nitrogen fixing bacteria, phosphate solubilising microorganisms, protein lysis bacteria, and nematode, etc. In addition, insects, mites, and their enemies inhabiting on papaya plants were also investigated. Our results indicated that there was no significant difference for all the investigated items between transgenic and non-transgenic papayas. These imply the transgenic papaya has no negative impacts to the ecological system. Based on the observation from the test field, the transgenic papaya lines were resistant to PRSV, but non-transgenic was not. However the transgenic plants were not completely immune for PRSV, since different degrees of symptom severity, from slight to medium mottling, were noticed among trees of the same line. Interestingly, another disease symptom caused by Papaya leaf-distortion mosaic virus (PLDMV) was found in some of the plants, including transgenic and non-transgenic, which were planted in the same place just after the three-year's open field trial. Based on this result, it was inferred that the interaction between transgenic papaya and the environment had begun after the plantation in the field. When the interaction has accumulated to certain degree, it may cause another viral disease to arise. Such a phenomenon needs to be further investigated in the future.