植物誘導性抗病之研究與應用

Abstract

植物具有潛在的抗病能力，可被外來因子活化，而在病原侵犯時表現防禦作用，阻礙病原的入侵、繁殖及蔓延，稱為誘導性抗病（induced resistance）。植物誘導抗病性一般在限制性感染、非病原微生物刺激或化學物質刺激的情況下產生。限制性感染時，寄主植物經常形成壞疽病斑，此為表現防禦反應以阻礙病原侵入，同時誘發植物對後續感染的抵抗性，此即所謂的系統性誘導抗病（systemic acquired resistance, SAR）或誘導系統性抗病（induced systemic resistance）。一般誘導抗病性對應的病原並不侷限於原誘導病原，可擴展至其他種類的病原，表現廣效的抗病性。近年來，藉由開發化學物質或非病原性微生物來誘發植物產生抗病潛能的方法，能促使植物在受到病原感染時能快速地表現抗病性，降低病原危害的程度，已有實用價值。化學物質中，包括水楊酸、撲殺熱具有誘發植物抗病潛能；而微生物如木黴菌、枯草桿菌亦相似效果。此等物質施用後，寄主體內的植物抗禦素（phytoalexin）、酚類化合物（phenol compounds）、植物防禦性蛋白質等在病菌入侵後會急速且大量增加與累積，增強抗病性與入侵病原對抗，達到防禦病害的效果。其中，亞磷酸誘導植物抗病的功效最佳，經常使用於卵球菌引起之病害（疫病、露菌病等）的田間防治。在國外，亞磷酸已被開發與商品化，如Foli-R-Fos 400 (20% H3PO3)，Nutri-Phite P Foliar (4% N-30% P2O5-8% K2O)，及Guard PK (7% N-21% P2O5-21% K2O)。而農試所於近年研發出一種簡單配製亞磷酸的方法，使用者與農民可以自行配製。其方法是將工業級的亞磷酸(95-99%)與氫氧化鉀(95%)以一比一等重使用，先將需用量的亞磷酸溶於水中，再溶解氫氧化鉀，調配好的亞磷酸的酸鹼值約pH6.0-6.2，可直接使用，可以減少調配亞磷酸酸鹼值時的費時與費工，並避免溶液於保存時，因氧化作用而導致藥效降低的情形。目前依照上述方法，亞磷酸普遍被農民用於蘭花疫病、番椒疫病、多種作物疫病與露菌病的田間防治。 All plants have potential resistant ability, which could be activated by outside environmental factors, against pathogen infection and subsequent propagation and dissemination. This is called “induced resistance”, which includes acquired systemic resistance (ASR), induced systemic resistance (ISR) and others. The induction of resistance was initiated and enhanced when plants were infected by local lesion pathogens or non-pathogens, or stimulated by certain chemicals. The induced plants would increase ability to fight against subsequent infection by the same pathogen and as some other pathogens. Phytoalexin, phenolic compounds, or pathogenicity related (PR) protein were produced and accumulated speedily in the responding plants to a certain level to fight against the invasion after pathogen infection. Recently, many microorganisms and chemicals, which could activate the induced resistance system in plants, have been investigated. Some of them could be used and applied to the field for disease control. Microorganisms included Tricoderma, Bacillus and many plant growth promoting rhizobacteria, while chemicals included salicylic acid and certain fungicides. Phosphorous acid (H3PO3) and its salts (phosphite or phosphonate) also have the ability to initiate the resistance in host plants. They are reduced phosphorus compounds, which could be used as a fertilizer. Currently, most researchers believes that phosphorous acid has both direct (plant protection) and indirect (host defense) modes of actions, but plant defense induced by the chemical is more important in breaking down pathogen’s attack. Commercialized products of phosphorous acid includes fungicide such as Foli-R-Fos 400 (20% H3PO3) and fertilizers such as Nutri-Phite P Foliar (4-30-8) and Guard PK (7-21-21) for diseases control. These products are commonly used for control of avocado root rot and citrus foot and root rot caused by Phytophthora species, downy mildew of grape, lettuce and crucifer and many other diseases caused by members of oomycetes. Recently, a simple method for phosphorous acid application was developed in the senior’s laboratory. It consists of dissolving equal amount (w/w, i.e. 1:1 in ratio) of phosphorous acid (H3PO3, 92-95%, industry grade) and potassium hydrochloride (KOH, 92-98%, industry grade) in water. The pH of the resulting solution is about 6.0 to 6.2, which is not phytotoxic to plants. The major diseases successfully controlled in the fields with this technique in Taiwan included late blight of potato and tomato caused by Phytophthora infestans, blight of pepper caused by Phytophthora capsici, root rot of avocado caused by Phytophthora cinnamomi, black rot of orchid caused by Phytophthora palmivora and Phytophthoa parasitica, and fruit downy blight of litchi caused by Peronophythora litchii.