- 學位論文
殺菌劑之移行性及對樹木褐根病之防治效果
Translocation of fungicides and their efficacy on controlling brown root rot of trees
摘要
褐根病由木材白腐菌Phellinus noxius所引起，其在熱帶及亞熱帶地區可感染超過200種木本植物，遭受感染之樹木根部及莖基部腐朽易有傾倒之風險，造成潛在的公共安全問題。現今臺灣褐根病防治登記藥劑僅有撲克拉，此外，由於褐根病菌主要感染樹木根部，在防治時難以均勻地將殺菌劑施用在受感染組織，而為了達到最大之防治效果，以及避免長期使用單一藥劑導致抗藥性之發生，在選擇防治用藥時應篩選具有良好系統性且不同作用機制之殺菌劑。本研究首先將14支不同作用機制之殺菌劑，以0.1 ppm、1 ppm及10 ppm之含藥培養基，測試39株P. noxius菌株 [採集自臺灣 (4株)、香港 (4株)、馬來西亞 (4株)、澳洲 (5株) 及美屬太平洋群島 (16株)] 的抑制效果，結果顯示屬於Fungicide Resistance Action Committee所訂定作用機制 (Mode of Action, MoA) 中G1類之殺菌劑抑制效果最佳，尤其是環克座、得克利及依普座於1 ppm下可達97.7-99.8%之抑制率，而賽普護汰寧 (MoA-D1 + E2) 及滅普寧 (MoA-C2) 也具有良好之抑制效果，於10 ppm下分別具76.7-100%及79.1-100%之抑制率。另外，發現所有分離自American Samoa之褐根病菌株對滅普寧皆存在抗藥性，經解序後發現其在succinate dehydrogenase subunit C (SDHC) 胺基酸序列發生三個點突變，其中S85A及V173I可能為造成抗藥性發生之主因。為評估藥劑之移行性，透過根部浸泡及莖部注射之方式施用滅普寧、環克座、得克利、依普座、撲克拉及賽普護汰寧於茄苳 (Bischofia javanica) 實生苗進行測試，並於7天及21天後利用液相或氣相層析串聯式質譜儀進行殘留量分析，發現所有測試藥劑皆不具向下移行之能力，而環克座及得克利具有顯著較佳之向上移行性，依普座較弱，而撲克拉、滅普寧、賽普洛及護汰寧之移行能力則相當有限。而利用莖部注射之方式，於施藥後21天得克利、依普座及賽普洛向上移行能力顯著優於其他藥劑，可能由於依普座及賽普洛難以被根部吸收，導致其於根部浸泡系統中移行性不佳。最後透過上述六支殺菌劑及亞磷酸鉀的土壤澆灌並配合P. noxius 2248之人工莖部接種茄苳苗，評估殺菌劑藉由向上移行以防治褐根病之能力，發現在莖部變色面積、分離率及P. noxius菌量分析上，各個藥劑處理與對照組間並無顯著差異，可能與接種過於強勢有關，未來有待進一步以田間試驗評估藥劑在成樹之預防及治療效果。
並列摘要
Brown root rot (BRR), caused by a white rot fungus Phellinus noxius, is a devastating disease of over 200 species of woody plants in tropical and subtropical areas worldwide. Infected trees with root and basal stem rot can toppled over, which poses a potential threat to public safety. Currently, prochloraz is the only registered fungicide for BRR in Taiwan. Besides, since P. noxius can colonize the underground root system, it is difficult to apply fungicides to all infected tissues. To achieve maximum chemical control of BRR and deter the emergence of fungicide resistance due to long-term use of a single fungicide, it is necessary to screen for good systemic fungicides of different modes of action. In this study, 14 fungicides were tested for inhibitory effects in vitro on 39 P. noxius isolates from Taiwan (4 isolates), Hong Kong (4 isolates), Malaysia (4 isolates), Australia (5 isolates), and other islands in Pacific Ocean (16 isolates), using potato dextrose agar containing 0.1, 1, and 10 ppm of each fungicide. Results showed that the fungicides belonging to G1 group [mode of action (MoA) classified by Fungicide Resistance Action Committee], in particular cyproconazole, epoxiconazole, and tebuconazole, inhibited colony growth of P. noxius by 97.8–99.8% at 1 ppm. Other effective fungicides were cyprodinil (MoA-D1) + fludioxonil (MoA-E2) and mepronil (MoA-C2), which showed growth inhibition of 76.7-100% and 79.1-100% at 10 ppm, respectively. In addition, all P. noxius isolates from American Samoa, which exhibited resistance to mepronil, carry three point mutations in succinate dehydrogenase subunit C (SDHC) amino acid sequence. The S85A and V173I substitutions in SDHC might be attributed to the mepronil resistance. To evaluate the translocation efficiency of fungicides, six fungicides included mepronil, cyproconazole, tebuconazole, epoxiconazole, prochloraz, and cyprodinil + fludioxonil were applied to bishop wood (Bischofia javanica) seedlings by root-dipping and stem-injection methods, followed by liquid or gas chromatography tandem-mass spectrometry analyses at 7 days and 21 days post treatment (dpt). All tested fungicides couldn’t translocate basipetally. Cyproconazole and tebuconazole showed significantly higher acropetal mobility among tested fungicides, epoxiconazole showed lower acropetal mobility, whereas mepronil, prochloraz, and cyprodinil + fludioxonil showed limited acropetal mobility. In the stem-injection system, tebuconazole, epoxiconazole and cyprodinil showed significantly higher acropetal mobility at 21 dpt. The poor uptake of epoxiconazole and cyprodinil by roots may result in low accumulation detected in the root-dipping system. To test for the efficacy of BRR control by acropetal translocation of fungicides, the abovementioned six fungicides and potassium phosphite were drenched before or after stem inoculation of P. noxius isolate 2248 in bishop wood seedlings. Nonetheless, no significant difference was observed between fungicide treatments and control in the percentage discoloration area of the stem, isolation frequency, and biomass of P. noxius. The ineffectiveness may be due to overly high inoculation strength. In the future, the preventive and curative control efficacy of these fungicides needs to be evaluated in mature trees in the field.