臺灣桉樹葉部病害之研究

Abstract

臺大植物醫學研究室於2013年承接福德坑環保復育公園造林計畫，而該地栽植的部分尾葉桉卻出現葉斑病發生嚴重落葉情形，經調查發現是過去不太需要注意，目前卻變成嚴重的桉樹角斑病，因為不太需要進行防治，於從2014年開始對福德坑環保復育公園的尾葉桉角斑病進行流行病學的調查與藥劑測試。另也參與台北市建國假日花市植醫診所的計畫及2015年臺北市374座鄰里公園樹木健康檢查計畫，於植醫診所收到攤商加寧桉的新紀錄病害，而在公園樹木健康檢查計畫中則發現常見綠化樹種大葉桉上常出現特定的病斑，經鑑定調查之後發現為臺灣過去沒有報導過的病害，遂對其進行研究。本研究對上述三種桉樹的病斑分離出病原菌，經鑑定並完成柯霍氏法則後，確認引起尾葉桉角斑病病原為Phaeophleospora spp.、引起加寧桉葉斑病並原為Pestalotiopsis spp.，而引起大葉桉葉斑病病原則為Pseudoplagiostoma eucalypti。對尾葉桉角斑病流行病學的調查之，發現發病嚴重度最高多在5至11月，對照當地氣候紀錄進行相關分析，結果發現角斑病的發病嚴重度和溫度有高度相關。以角斑病孢子在不同溫度下發芽測試，發現最適發芽溫度為25℃，且低於15℃或高於35℃孢子都會無法發芽。對病斑以藥劑處理測試是否能藉施藥降低病斑上病原菌的再分離比率，結果顯示甲基多保淨處理後的病斑再分率有顯著的下降。 本研究調查鄰里公園大葉桉上葉斑病的分布，發現此病普遍存在於臺北市大葉桉上。對大葉桉葉斑病的孢子與菌絲做溫度生理試驗，結果顯示孢子在35℃時發芽率達到越高，菌絲生長則在25℃時達到最高。以藥劑測試是否能降低病斑上病原菌的分離率，結果顯示以銅快得寧處理的組別病原菌的分離率有顯著的下降。本研究由加寧桉葉斑病分離出的兩支Pestalotiopsis spp.菌株GC01與GC02，其溫度生理測試的結果顯示兩支菌的菌絲都在25℃達到最快速的生長。而以甲基多保淨與待克利兩支藥劑測試菌絲生長的結果，則是待克利對菌株GC02的抑制效果較佳，與甲基多保淨間有顯著的差異；而對菌株GC01而言則是兩種藥劑皆有效果，且兩者之間都沒有顯著的差異。

Since NTU Plant Medicine Laboratory undertook the afforestation program for Crawford Hang Environmental Remediation Park in 2013, the cultivated Eucalyptus urophylla has shown serious leaf spot and defoliation symptoms.We initiated this reseach thereafter and found that this disease is an angular leaf spot diseases of Eucalyptus which was reported to be a mild disease but has currently become a serious one in Taipei area. We therefore investigated its epidemiology and tested pesticide effects for controlling this disease in Crawford Hang Environmental Remediation Park in 2014. The author has also participated in the plan of Plant Clinics in Chien Kuo Holiday Flower Market of Taipei and the Tree Health Inspection Project for 374 parks in Taipei during 2015. One newly recorded disease of Eucalyptus gunnii was identified on the seedling from a vendor, and the other newly recorded disease was found on the leaf of Eucalyptus robusta, a common tree species in Taiwan, during the Tree Health Inspection Project. In this study, all the three pathogens were isolated from the lesion of the Eucalyptus species. The disease pathogen on Eucalyptus urophylla was identified as Phaeophleospora spp., while that on Eucalyptus robusta was identified as Pseudoplagiostoma eucalypti and that on Eucalyptus gunnii was identified as Pestalotiopsis spp., respectively. The Koch's postulate was conducted for all three diseases to prove the pathogenecity of all three pathogens. The pathogens were inoculated to the healthy Eucalyptus plants and the same symptoms could also be reproduced. The reisolation of the three pathogens were all successful, indicating that the diseases were caused by the parhogens. Results of epidemiology study on angular leaf spot showed that this disease was more serious in the period from May to November than that in the other period. The correlationship analysis showed that the severity of the angular leaf spot disease was correlated with warmer temperature. The optimal temperatures for spore germination were measured on Phaeophleospora spp. with results showing that the germination rate was the hightest at 25℃, while the spores were unable to germinate at temperature lower than 15℃ or higher than 35℃. We also sprayed some pesticides on the diseased Eucalyptus to test whether it can reduce the pathogen isolation rate. Results showed that the lesions of angular leaf spot sprayed with thiophanate-methyl had lower isolation rate a the others. The field investigation results showed that the leaf spot of Eucalyptus robusta is a widespread disease in urban parks in Taipei area. The optimal temperature for spore germination is 35℃ for Pseudoplagiostoma eucalypt, while the optimal one for mycelium growth is 25℃. The results of fungicide tests showed that oxine-copper can significantly reduced the pathogen isolation rate on spryed lesions of this leaf spot disease. Two Pestalotiopsis spp. strain GC01 and GC02 were isolated from the leaf spot of Eucalyptus gunnii. The optimal temperature for hyphae growth of both strains were at 25℃. The fungicide test for inhibiting the hyphae growth showed that difenoconazole was more effective than the thiophanate-methyl against the strain GC02, while to strain GC01, both fungicide were effective with no significant difference between them.