健康種苗生產技術與果樹產業

Abstract

台灣地處亞熱帶，平原地區氣候溫暖潮濕，較適合熱帶型果樹之生長。但全島有三分之二面積屬於山地，甚至包括三千公尺以上高山，氣候與地形多變，故部分地區亦極適合溫帶型果樹之生產。因此自光復以來台灣地區曾經推廣發展之果樹產業種類繁多，幾乎涵蓋全球各地主要消費之果樹種類。果樹之生長通常需要較長的苗木期才能成長至果實豐產期，因此其面臨病害的挑戰相較於其他短期作物更為嚴苛，否則難以渡過苗木期而獲得理想的產量回饋。記錄上威脅果樹的病害種類中，以會造成系統性感染而隨苗木之無性繁殖垂直傳播至幼苗的病毒(virus)、類病毒(viroid)與菌質(phytoplasma)等病害影響最為嚴重。加上此等病害均無法輕易以藥劑防治加以治癒，果樹一經感染常無法維持正常之生長與結實。除了透過苗木的無性繁殖而傳播外，這些病原在田間也可以經由適當的媒介昆蟲或其他生物傳染至其他健康之植株，或遠距離散佈至其他地區，擴大其威脅的範圍。為了對抗此等病害，自古以來農業界已經深知除了清除田間感病的植株，降低感染源密度外，必須栽培健康無病之苗木才能維持果樹之正常生長與產能。因此建立一套穩定繁殖與供應無病健康果苗之體系乃任何面對此項威脅的果樹產業必要之因應作為。從技術層面上來看，無病健康果苗之生產體系必須包括以下幾項：一、無病種源之篩選與確認：二、優良品系之去病原(或無毒化)技術；三、無病種源之保存；四、無病果苗之繁殖與量產。不過一個果樹之無病毒種苗要真能在田間發揮理想之防治效果，除了上述技術外更重要的層面是如何能抑制或延緩無病果苗於田間再次被感染之機會，保護其成長期間之健康無病狀態，以促成其未來之豐產與回饋。因此無病果苗之田間栽植與保護技術其實在應用層面上與果苗之繁殖技術同等重要。本文將以幾種本土果樹為例，介紹建立健康果苗生產之技術與田間應用時應把握之要領，以供台灣果樹產業發展各方先進之參考。 Taiwan island, although situates within subtropical region, has very diversified geography and environment. In the plane region, its warm and humid environment is suitable for the cultivation of most tropical and subtropical fruit crops. While in its mountain area, which covers almost two thirds of Taiwan’s total acreage, owns highly diversified altitudes and environments and is also appropriate to grow fruit trees of temperate zone. Taking such advantages on environmental conditions, nearly all kinds of well known fruit crops have been successfully cultivated in Taiwan since 1950s. Most fruit trees need longer vegetative growing period before fruit yielding stage. This makes fruit crop cultivation more challenging especially on pest protection than other crops. Among the diseases that threaten fruit trees, those cause systemic infection and can transmit vertically from mother plants to their vegetative growing materials, such as viruses, viroids and phytoplasmas, are considered to be more dangerous and economically important. Once infected by these pathogens, most fruit trees will gradually lose their vigor and productivity and more importantly most of these diseases can not be cured by any treatment including chemotherapy. Furthermore, most of these pathogens can be transmitted efficiently and long distantly by insect vectors. These properties make cultivation of fruit trees suffering such diseases a highly challenging task. To combat against these diseases, past experience has consistently shown that the most effective control strategy is to eradicate diseased trees in the field and replanted with disease free young trees. Therefore, to establish an efficient disease free fruit tree propagation system is necessary for the implementation of control strategy on most fruit crops. Technically, in order to establish a disease free fruit tree propagation program, there are at least four parameters should be considered. 1.Techniques for screening and confirming disease free growing materials. 2.Techniques for elimination of pathogens from cultivars or clones with good horticultural traits. 3.Techniques to maintain and protect disease free growing materials from re-infection. 4.Techniques for mass reproducing disease free growing materials efficiently and economically. Besides these techniques related to the production of disease free fruit trees, actually there is another parameter should be considered once the disease free materials are available. That is how to protect the disease free materials from early re-infection when they are transplanted into the open fields. Without appropriate protection scheme those disease free young trees may re-infected quickly before maturation and lose their productivities. In this article, experience accumulated from the past two decades will be used as examples to explain the application of disease free fruit tree to control diseases caused by virus and virus-like pathogens.