桶柑鱗砧病之研究

Exocortis in Tanken(Citrus tankan Hay.)

在臺灣大學進行之Etrog枸櫞指示試驗，顯示苗圃桶柑樣本中之鱗砧病發生率甚低。在臺灣中部及北部桶柑園調查壹千株以上之廣東（木黎）檬砧之桶柑，亦未發現明顯之鱗砧病病徵。由此可知鱗砧病可能不是桶柑固有之病害，或是桶柑僅帶有不致引起廣東（木黎）檬發生可見病徵之緩和系麟砧病毒。據目前所知鱗砧病對臺灣之桶柑似乎並未構成嚴重之問題。不過，也於田間屢見發生於外來甜橙及檸檬品種之廣東（木黎）檬砧木典型病徵，新近復知此病能藉用具或手指而傳染之特性，故對此病在臺灣傳佈之危險性仍然極大，殊應加以防患。在繁殖方面，應注意選擇經證質不帶鱗砧病毒之母本材料，並嚴格執行用具之消毒及避免手指之污染以杜此病之蔓延。鱗砧病指示法比較試驗中，本實驗所用枸櫞切接指示法，不論在發病時間上或發病率方面，較諸卡氏標準複芽指示法者均較良好，殊有作更進一步試驗之價值。

Etrog citron indexing experiment carried out in National Taiwan University showed low incidence of exocortis in selected tankan nursery tree samples. Field observation of more than 1,000 tankan on Rangpur lime stock in central and northern Taiwan showed that no conspicuous exocortis symptom being encountered. There is possibility that exocortis originally was not a latent disease of tankan, or tankan carries only a mild strain of exoeortis which cause no recognizable symptoms on Rangpur lime stock. It is very likely that the existence of exocortis did not seem to constitute serious problem of tankan in Taiwan. Nevertheless, the frequent occurence of exocortis in the imported sweet orange and sour lemon varietes plus the fact that this viroid disease is contagious through contaminated tools and fingers necessitate great precaution. The practice of using only exocortis-free propagating materials and tool disinfection should be followed to prevent from the spreading of exocortis viroid in Taiwan. Noticeable differences in time requirement and frequency for symptom expression of exocortis between the simu1taneous budding and the bud inoculated top-grafting methods in this experiement were of interest. The latter method justisfies further trial for the betterment of indexing for exocortis viroid in Taiwan.