黃皮與枳殼對線蟲抗性機制之掃描式電子顯微鏡觀察

SEM Observation on the Nature of Resistance of Wampi and Trifoliate Orange to Nematode Infection

本研究室近年來發現酸、甜二種黃皮（Clausena lansium）對根腐線蟲（Pratylenchus coffeae）具有抗性，而臺灣常用柑桔砧木－－廣東（木黎）檬（Citrus limonia Osbeck）屬於高度罹病性。另外，由美國引進之飛龍及波馬麗枳殼（Poncirus trifoliata）對柑橘線蟲（Tylenchulus semipenetrans Cobb）具高度抗性，但粗皮檸檬（Citrus jambhiri Lush）則屬高度罹病性。故本文試圖研究構造變化與抗性機制之關係。光學顯微鏡觀察結果顯示植物根部受根腐線蟲為害之主要部位為皮層，而柑橘線蟲則可為害表皮與皮層。配合以掃描式電子顯微鏡之觀察結果，顯示在抗性黃皮與枳殼之根中，所有入侵的線蟲會迅速被許多壞死及／或厚壁細胞所包圍，因此線蟲會被隔離而堵住，故無法進一步為害。但罹病性之廣東（木黎）檬及粗皮檸檬，雖也有細胞壁之增厚反應，但程度低，且僅限於局部，速度亦較慢，故線蟲可進一步為害其他細胞。另外掃描式電子顯微鏡可清楚地觀察到受根腐線蟲為害後的根中，會有一些未經鑑定的物質出現於細胞質中，此類物質是否與抗性有關，值得進一步探討。總之，本研究指出，芸香科植物對根腐線蟲的抗性機制，可用抗性植物根部細胞的迅速增厚能力來解釋，但對柑橘線蟲之抗性，則細胞壁增厚之程度較不明顯，顯然需要配合其他因子來達成抗性。

Previous citrus rootstock screening tests had shown that both sweet and sour wampi (Clausena lansium) were resistant to root-lesion nematode (Pratylenchus caffeae), while rangpur lime (Citrus limonia Osbeck) was susceptible. Also some U. S. selections of trifoliate orange (Poncirus trifoliata) e. g. Flying Dragon and Pomeroy trifoliates were highly resistant to citrus nematode (Tylenchulus semipenetrans Cobb), while rough lemon (Citrus jambhiri Lush) was highly susceptible. This study tried to find out whether structural changes of plant related to the nature of resistance. Light microscopic study showed that cortex was the main portion of root for the infection of root-lesion nematode, while citrus nematode infected both root surface and cortex. Together with SEM study, the results showed that in root system of nematode resistant wampi and trifoliate orange, all the invading nematodes were rapidly surrounded by necrotic and/or thickened-wall cells. Thus the nematodes were isolated and no further injury was induced. But in susceptible rangpur lime and rough lemon, after nematode infection, only part cell walls were thickened, so more cells were injured. SEM results also showed that there were some unidentified materials formed in the root-lesion nematode infected cytoplasm. Further investigation should be conducted to ensure their role in nematode resistance. In conclusion, in Rutaceae it seems proper to explain the nature of plant resistance to root-lesion nematode by rapidly thickening of root cell walls. But because the degree of cell wall thickening was less in resistant trifoliate orange than the infection of citrus nematode, therefore, it was suggested that some other factors should be considered.