- 期刊
台灣胡蘿蔔黑色根腐病－病原菌的鑑定與影響病害發生的因子
Carrot Black Root Rot Caused by Thielaviopsisbasicola - identification of the Pathogen and Factors Affecting its Occurrence in Taiwan
摘要
西元2011年於台中市菜市場發現胡蘿蔔塊根出現灰黑色黴狀病斑，造成整個胡蘿蔔塊根變黑壞死。從罹病胡蘿蔔塊根進行組織分離，得到三株病原眞菌（CT01、CT02及CT03）均可感染菸草幼苗與胡蘿蔔塊根，造成菸草根腐與矮化及胡蘿蔔塊根黑變壞死。在蔬菜瓊脂（V8 juice agar）平板上，分離菌株菌落呈現墨綠色至灰褐色，可以瓶狀產孢細胞行內壁芽生方式產生無色單孢、鏈狀排列的長橢圓形分生孢子外，並可以菌絲末端特化方式形成厚壁含油滴的短圓柱形、深褐色厚膜孢子。定序分析以專一性引子所增幅之核醣體去氧核醣核酸之轉錄區間內序列（internal transcribed spacer, ITS），發現此三眞菌菌株與T. basicola相似度達98-99%。綜合三菌株之形態、特徵、ITS序列分析及致病性，確定它們的學名為Thielaviopsis basicola。T. basicola最適菌絲生長及孢子發芽溫度為24℃；孢子發芽最適酸鹼值介於6-8之間。將孢子懸浮液滴於胡蘿蔔塊根表面，發現最適發病溫度為20至24℃間，其中尤以具傷口之胡蘿蔔的發病程度最高，當每個接種點的菌量達1個分生孢子以上，即可使胡蘿蔔發生黑色根腐病。此外，當相對溼度低於85%時病害不發生，超過93%時病斑開始顯現，相對濕度97.5%以上病斑面積擴展尤為顯著，且罹病面積與其產孢量呈正相關。研究發現，以菜瓜布刷洗者，塊根病斑擴展最為明顯，其次則為海綿刷洗者，至於僅以人工清洗者，則塊根不會產生病斑。此外，嘗試探討生物及非生物資材對胡蘿蔔黑色根腐病發生的影響，結果顯示醋酸、二氧化氯及Pichia kudriavzevii拮抗微生物均可顯著抑制病原菌的孢子發芽及減輕病徵的擴展，頗具有推薦作為防治胡蘿蔔黑色根腐病資材之潛力。
並列摘要
Black root rot of carrot (Daucus carota L.) caused by Thielaviopsis basicola (Berk. & Broome) Ferraris (syn. Chalara elegans Nag Raj & Kendrick) is one of the most important diseases occurred in fresh carrot markets in Taiwan. The typical symptoms are black mold patches appearing on affected carrot roots. When infection is severe, mold-like lesions coalesce to cover the entire root surface, resulting in dark necrosis. Carrot rots of unknown etiology were found in a local market in Taichung in summer _2011. Three fungal isolates, designated CTO1, CTO_2 and CTO3 were cultured from diseased carrot roots. Inoculation tests on carrots and tobacco seedlings, causing root rot and stunting of tobacco seedlings and root rot on carrot root tubers, confirmed their pathogenicity. Comparison of ribosomal DNA internal transcribed spacer (ITS) sequence against those in the database confirmed that CTO1, CTO_2, and CTO3 are closely related to Thielaviopsis basicola. Field surveys revealed that T. basicola was present at low levels in carrot-producing areas in Taiwan. In-vitro studies indicated that the optimum temperature for T. basicola growth and conidial germination was around _24℃ and the optimum pH ranging from 6 to 8. Inoculation assays identified the factors that could influence the occurrence of carrot black root rot disease. The optimum temperatures for fungal colonization and disease development ranged from 20 to 24℃. Wounding carrot prior to T. basicola inoculation enhanced root rot development and lesion severity. Both relative humidity (RH) and soil pH affected the occurrence of black root rot. No root rots were observed when RH was kept below 85%. Lesion sizes were positively correlated (r＝O.98) with the number of conidia on the lesion. The severity of carrot black root rot was found to be affected by the method of washing prior to storage. Scrubbing with a sponge injured carrot root surface and facilitated the development of black rot lesions. As many plant diseases, the incidence and severity of carrot black rot were affected by inoculum concentration, wounding, temperature and relative humidity. In this study, efforts were also undertaken to explore possible abiotic or biotic materials for controlling carrot black root rot disease. Of all materials tested, acetic acid, ClO_2, and Pichia kudriavzevii significantly reduced conidial germination of T. basicola and lesion development induced by this pathogen.