台灣芥菜黃葉病菌的鑑定及其致病性

Identification for the causal agent of mustard yellows in Taiwan and its pathogenicity

"西元2010至2016年間在雲林西螺、高雄梓官、桃園蘆竹及台中等地區之蔬菜栽培田，發現芥菜植株呈現下位葉黃化、單側偏上生長、矮化等現象，其莖基部的維管束則有褐化病徵。將芥菜罹病植株之褐變部位進行可疑病原菌的分離，共獲得8個菌株，經過柯霍氏法則系列驗證，結果顯示各菌株對芥菜皆具有不同程度之致病毒性。本病原菌FOCN05與FOCN38菌株生長於馬鈴薯葡萄糖瓊脂培養基之菌落，初期為白色菌絲向四周延伸，在光照下逐漸轉變為淺紫色，後期於菌落表面出現散生的橘黃色孢子叢，生長最適溫度為28℃。本病菌有大、小分生孢子及厚膜孢子三種形態，大分生孢子呈鐮刀狀，無色，平均大小為34.4~36.8×3.9~4.5μm；小分生孢子數量較大分生孢子多，橢圓形，單胞無色，平均大小為6.4~8.2×2.5~3.1μm；厚膜孢子呈圓形，多以間生或頂生的方式形成於菌絲上，平均大小為9.6×8.7μm。將12種十字花科蔬菜及其他蔬菜種子，分別播種於FOCN05與FOCN38菌株之病菌土中，結果發現本病原菌對葫蘆科、菊科、豆科、茄科等作物不具致病性外，亦不感染甘藍與芥藍植株；惟對芥菜、白菜及蘿蔔皆有致病性。綜合本研究之菌株形態、致病特性及核糖體DNA基因間隔區間（intergenic spacer）之親緣性分析結果，筆者建議將台灣的芥菜黃葉病菌學名鑑定為Fusarium oxysporum f. sp. rapae（Enya, Togawa, Takeuchi & Arie）。"

"The causal agent of mustard yellows was isolated from diseased plants collected from vegetable fields at Yunlin, Kaohsiung, Taoyuan, and Taichung in Taiwan. The disease is characterized by yellowing on the lower leaves, epinasty, stunted and appeared brown in the vascular tissue. In this study, eight isolates were obtained, and their pathogenicity was confirmed via the steps of Koch's postulates. On potato dextrose agar plate, the mycelia of isolates FOCN05 and FOCN38 are colorless at first, but with age they become purplish under 12hr-light per day and produce orange sporodochia. The optimum temperature for mycelial growth of FOCN05 and FOCN38 was at 28℃. The pathogen produces three kinds of asexual spores. Macroconidia were slightly sickle-shaped, hyaline, 34.4~36.8 × 3.9~4.5 μm. Microconidia were elliptical to allantoid, one-celled, hyaline, 6.4~8.2 × 2.5~3.1 μm. Chlamydospores form mostly in hyphae, terminal or intercalary, round, thick-walled, about 9.6 × 8.7 μm. In addition, pathogenicity tests indicated that isolates FOCN05 and FOCN38 were able to infect mustard, radish, and pak choi. However, no symptom showed in other family crops and cabbage and Chinese kale. According to the results of pathogenicity tests, morphological characteristics, and ribosomal DNA intergenic spacer (IGS) sequence, it was suggested that the scientific name of the causal agent of mustard yellows from Taiwan could be identified as Fusarium oxysporum f. sp. rapae (Enya, Togawa, Takeuchi & Arie)."