臺灣茶赤葉枯病菌族群對免賴得及甲基多保淨之感受性分析

Analysis of the sensitivity to benomyl and thiophanate-methyl for Colletotrichum spp. associated with brown blight of tea in Taiwan

赤葉枯病菌主要危害茶樹葉片與幼嫩枝條，造成茶葉品質及產量下降，茶農主要依賴化學藥劑進行防治，然近十年茶農開始反應登記之殺菌劑藥效不佳。為瞭解臺灣茶赤葉枯病菌族群是否已對methyl benzimidazole carbamate（MBC）類藥劑產生抗藥性，本研究對來自臺灣8個主要產茶縣市之37株Colletotrichum camelliae、3株C. fructicola及1株C. aenigma，測試在含有效成分1,000 ppm（mg a.i./L）、100 ppm、10 ppm、1 ppm的免賴得及甲基多保淨藥劑之馬鈴薯葡萄糖瓊脂培養基上菌絲生長情形，結果顯示除了分離自屏東之C. camelliae菌株皆有抗藥性外，其他縣市之C. camelliae菌株可分為對藥劑呈敏感性及高抗性兩群，而C. fructicola及C. aenigma菌株則皆對藥劑呈敏感性。41株受測菌株對兩藥劑的感受性有相同趨勢，且抗性菌株對甲基多保淨的感受性更低。針對不同縣市之15株C. camelliae，分析β-tubulin基因中已知最常發生抗藥性突變之區段，發現高及低感受性菌株僅在第860個核苷酸具有差異，此一點突變造成第198胺基酸由glutamic acid（GAG）變成alanine（GCG），符合文獻中造成高度抗藥性之機制。茶赤葉枯病菌對兩藥劑之感受性與田間管理方式具相關性，高抗性菌株皆分離自慣行茶園，而分離自有機管理或用藥較少的茶園之菌株，對測試藥劑皆呈敏感性。本研究顯示臺灣各茶產區已普遍存在對MBC類藥劑具抗性之C. camelliae菌株，建議應落實不同作用機制藥劑之輪替或混合使用，並結合整合性管理措施，以有效防治本病。

Brown blight disease mainly damages tea leaves and young branches, resulting in a decline in tea quality and yield. Tea farmers mainly rely on chemical control, however, in the past ten years, they have reported that the registered fungicides are not effective. To understand whether the population of the pathogen associated with brown blight of tea in Taiwan has emerged resistance to methyl benzimidazole carbamate (MBC) fungicides, 37 isolates of Colletotrichum camelliae, three isolates of C. fructicola, and one isolate of C. aenigma from eight major tea-producing counties and cities in Taiwan were tested for mycelial growth on potato dextrose agar containing 1000 ppm (mg a.i./L), 100 ppm, 10 ppm, and 1 ppm of benomyl and thiophanate-methyl. While C. camelliae isolates highly and lowly sensitive to the fungicides were found in each county/city (except that C. camelliae from Pingtung County were all resistant), the isolates of C. fructicola and C. aenigma were all highly sensitive. All 41 isolates tested showed similar trend of sensitivity or resistance to the two fungicides, and the sensitivity of the resistant isolates to thiophanate-methyl was lower. For 15 isolates of C. camelliae from different counties and cities, a segment of β-tubulin that is known to have the most frequent fungicide resistance mutations was sequenced. The sensitive and resistant isolates differed only at the 860th nucleotide, which caused the 198th amino acid changed from glutamic acid (GAG) to alanine (GCG). The phenomenon conforms to the mechanism of the emergence of high fungicide resistance in the literature. The fungicide sensitivity of Colletotrichum spp. associated with brown blight of tea was related to the modes of management in the field. The resistant isolates were all from conventional tea plantations, and the isolates from the plantations organically managed or with less fungicide application showed high sensitivity. This study indicated that C. camelliae isolates resistant to MBC fungicides have been widely present in many tea-growing areas across Taiwan. It is recommended that rotation or mixed use of fungicides with different modes of action, together with integrated pest management measures should be implemented to effectively control the disease.