葉用甘藷根莖腐病之研究

Abstract

2006年於台北縣樹林鎮、永和市首先發現所種植之葉用甘藷發生植株葉片萎凋、部分莖組織褪色的病徵，嚴重者莖基部黑色軟腐、全株產生缺水枯死、根部腐敗，最後造成全株死亡。詢問當地農友得知，該病害的歷史可追溯到十年之前。經柯霍氏法則確認該病原為細菌。經形態觀察、革蘭氏染色測定、Biolog鑑定及NGM選擇性培養基鑑定，確認該病原為Erwinia chrysanthemi。該病原主要危害葉用甘藷的莖部與根部，造成莖基部黑腐與根部褐化軟腐，進而引起植株萎凋枯死，此與國外甘藷細菌性根莖腐病病徵極為相似且病原菌相同，因此稱之為葉用甘藷根莖腐病(root and stem rot)。由E. chrysanthemi引起之葉用甘藷細菌性根莖腐病為台灣之首次記錄。在品種抗性測定方面發現供試四種葉用甘藷品種中以永和種1號最為抗病，桃園2號、台農71號及永和種2號皆具感染性。以濾紙圓盤法測試市售9種藥劑在3種不同稀釋倍數下對根莖腐病菌菌株生長之抑制效果，顯示四環黴素對葉用甘藷根莖腐病之菌生長之抑制效果最佳，而嘉賜黴素對E. chrysanthemi無任何防治效果，其餘7種防治藥劑包括銅快得寧、氫氧化銅、鏈四環黴素、多保鏈黴素、鏈黴素、維利黴素、嘉賜黴素等實驗藥劑均能抑制E. chrysanthemi根莖腐病菌之生長。

Severe root and stem rot of sweet potato was first found in Yong-He and Shu-Lin, Taipei county, in Taiwan in 2006. The disease symptoms include wilting shoot, pale leaf, black stem, root rot and death. The occurrence of this disease can be traced back to at least ten years ago as described by the farmers. The causal agent of root and stem rot of sweet potato is a pathogenic bacterium according to Koch’s postulates. The pathogen was identified as Erwinia chrysanthemi based on the morphology, Gram’s stain test, Bilolog identification, and NGM differential medium test. The pathogen mainly attacked the root and stem and caused black rot of stem base, brown rot of root, and death. The symptoms were similar to those of the bacterial stem and root rot reported in United States, although in United States it majorly attacked the roots. This is the first report of this disease in Taiwan. Four varieties including “Taoyuan#2”, “Tainong#71”, “YongHe# 1” and “YongHe#2” were screened for the disease resistance “YongHe#1” had the highest resistance, while “Taoyuan#2”, “Tainong#71” and “YongHe#2” were sensitive to E. chrysanthemi. Nine bactericides at three concentrations were tested for their control effects on E.chrysanthemi by paper disc diffusion method. Among them, tetracycline has been proven to be the most effective, while oxine-copper＋copper hydroxide, cupric hydroxide, streptomycin sulfate + tetracycline, kasugamycin +copper oxychloride, thiophanate-methyl + streptomycin, streptomycin and validanmycin could inhibit the growth of E. chrysanthemi. However, kasugamycin alone was no effective to control this bacterial disease.