Acibenzolar-S-methyl 防治柑橘潰瘍病之效果及其誘導抗病機制之探討

Abstract

由Xanthomonas citri subsp. citri 所引起的柑橘潰瘍病為目前世界柑橘生產栽培最具經濟重要性的細菌性病害，銅劑為當前廣泛應用於防治柑桔潰瘍病之藥劑，但過度或長期使用容易誘發病原菌產生抗銅性。本研究調查雲林及嘉義地區之柑橘潰瘍病菌株對銅劑的感受性，於篩選之菌株中發現2 株抗銅菌株及46 株耐銅菌株。由於抗銅菌株可導致銅劑防治失效，有鑑於此，開發其他可施用並符合永續農業理念之防治方法有其必要性。本研究利用acibenzolar-S-methyl (ASM)、4-4 式波爾多液 (Bor) 及兩者同時配合使用 (ASM + Bor)，於溫室條件下進行對柑橘潰瘍病之防治效果評估。種植於盆栽之檸檬幼苗每株分別以土壤澆灌5 mg a.i. ASM、葉面施用4-4 式波爾多液或兩者配合同時施用，於處理後3 d 進行柑橘潰瘍病菌接種。結果顯示3 種處理之罹病度分別為19.14%、15.0% 及15.4%，與無處理之對照組 (39.96%) 具有顯著差異。進一步分析抗病相關酵素活性，結果發現單獨以ASM 處理之植株，其過氧化物酶 (peroxidase; POD) 及過氧化氫酶 (catalase;CAT) 之活性明顯增加。由以上結果可知，ASM 可有效降低植株對潰瘍病之罹病度，能藉由提高POD 與CAT 活性以誘導檸檬植株產生抗性而達到防治效果。 Citrus canker caused by Xanthomonas citri subsp. citri (Xcc) is one of the most economically important bacterial disease in the international citrus industry. The copper-based bactericides were widely use to or control citrus canker. However, frequent applications of copper-based bactericides induce the development of bacterial strains either resistant or tolerant to copper. In this study, Xcc strains were collected from citrus orchards in Yunlin and Chiayi of Taiwan and used to assess the sensitivity to copper on a solid medium. The tests identified two copper resistant strains and 46 copper tolerant strains. Copper resistance in plant pathogenic bacteria contributes to a failure to control plant bacterial diseases by copper bactericides. In view of this, it is necessary to develop alternative control methods for sustainable agricultural practices. In this study, the individual and combined effects of acibenzolar-S-methyl (ASM) and 4-4 bordeaux mixture (Bor) were investigated in a greenhouse to control citrus canker disease. Three treatments were conducted on potted lemon (Citrus limon) seedlings: soil drench with 5 mg a.i. ASM, foliar spray with Bor, and a combination of the above two treatments (ASM + Bor). The lemon seedlings were inoculated with Xcc 3 d post treatments. The results showed that the disease severities of ASM, Bor and ASM + Bor were 19.14%, 15.0%, and 15.4%, respectively, which were significantly different from the untreated control (39.96%). For the defence-related enzyme activity assay, progressive increases in peroxidase and catalase activities were found in lemon seedlings treated with ASM alone. Our results suggested that ASM was effective in reducing canker disease severity, mainly through enhancing the activities of peroxidase and catalase in planta.