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Biological Characteristics and Control of the Causal Agent of Cruciferous Vegetable Anthracnose
Cruciferous vegetable anthracnose
medicinal plant materials
|摘要:||西元1997年夏天，在台灣主要蔬菜栽培區如雲林縣、苗栗縣、新竹、花蓮、高雄與台中等地，發現許多白菜葉片出現淡黃色至灰褐色圓形斑，中間白色透明發亮，有時會有穿孔現象，多數病斑會癒合成大形壞疽斑；病斑主要發生於下位葉，嚴重時受害葉片會出現乾枯下垂的病徵；且此病害多發生於有機蔬菜栽培區。將罹病組織分離到的炭疽病菌回接於白菜，四天後，植株葉片即會產生如自然感染的病徵。進一步，將具病原性之菌株接種於甘藍、蘿蔔、芥菜、芥藍、不結球白菜、結球白菜、莧菜、茼蒿、萵苣、芹菜、甕菜及菠菜等蔬菜，結果發現甘藍、蘿蔔、芥菜、芥藍、不結球白菜會出現病徵。在馬鈴薯葡萄糖瓊脂平板培養此病原菌，其菌絲平鋪生長於培養基表面，呈白色或墨綠色至黑色，會產生鮭紅色分生孢子堆；分生孢子單胞，圓筒形或紡錘形，透明無色，內有大型油滴，大小平均為16.65×4.68mm ; 附著器呈圓形至不規則形; 分生孢子盤 (acervuli) 於葉表皮下埋生，孢子盤內散生剛毛，剛毛深褐色。綜合上述病原菌的形態、產孢方式及病原性等特性，進而與國內外相關文獻比較，並參照Sutton, B. C.出版The Coelomycetes, Fungi Imperfecti with Pycnidia, Acervuli and Stromata一書的分類系統，筆者將本病原菌鑑定為Colletotrichum higginsianum Sacc. apud Higgins。C. higginsanum的菌絲生長、分生孢子發芽及附著器形成的最適溫度皆為24-28 oC。病害之發生會隨溫度上升而提高。白菜接種病原菌後濕度維持20小時以上，植株的罹病度即可達80%以上。本病原菌可感染定經草 (lindernia antipoda (L.) Alston) 外，亦可在土壤中以寄主殘體存活35天以上。篩選8種藥用植材對C. higginsianum之分生孢子發芽與菌絲生長的抑制效果，發現丁香具有完全抑菌的效果。以不同濃度之丁香油處理病原菌之分生孢子，發現750 ppm丁香油可以完全抑制分生孢子發芽。利用光學顯微鏡和掃描式電子顯微鏡觀察處理過丁香油的病原菌，發現丁香油會使病原菌菌絲膨大變形外，亦會造成附著器之原生質外漏。比較丁香水溶性浸出液、丁香油及丁香酚防治白菜炭疽病的效果，結果顯示丁香油與丁香酚具有相等的防治功效，且較丁香浸出液的防治率高50% 以上。利用不同濃度之丁香油溶液防治白菜炭疽病，發現濃度高於1500 ppm 時，防治效果可達70% 以上；惟再提高施用濃度，其防治效果並無顯著提昇。在丁香油溶液中分別添加植物生長的基本元素N、P、K、Ca及Mg元素等鹽類，然後噴佈於植齡25天的白菜植體上，結果發現KNO3、H3PO3、K2SO4、Ca(NO3)2·4H2O及MgSO4等可顯著增進丁香油防治白菜炭疽病的效果。|
Since 1997, Pak-choi (Brassica rapa L. Chinese Group) anthracnose has become severe in organic farms at Yunlin, Miaoli, Hisnchu, Hualien, Kaohsiung and Taichung Counties in Taiwan. The symptoms consisted of small, circular to irregular, pale gray to straw-colored lesions occurring in lower leaves. The lesions may become perforated with splits through the dried necrotic area. Under favorable conditions, the numerous lesions often coalesce and form large irregular spots, and infected leaves become yellowing and wilting. Symptoms on mid-ribs, petioles and stems appeared as sunken and elongated lesions with gray to dark, brown or black border. The fungus was consistently isolated from diseased Pak-choi leaves and its pathogenicity was confirmed by spraying the conidial suspension onto the leaves of cruciferous and other families vegetables. The symptoms developed only on inoculated plants of cruciferous vegetables. Other inoculated plants remained symptomless. The colonies of the pathogen on PDA plates usually had little aerial mycelia, but occasionally produced fluffy patches of white aerial mycelia or produced the dark mycelial bodies onto the agar. Conidia were produced in dense, continuous, cinnamon-colored and setae were not developed in culture, but were produced on the host. The pathogen produced rod-shaped, rod-ends, hyaline, one-celled conidia in acervuli. Average of conidial size was 16.65×4.68μm. According to the morphology and the pathogenicity on cruciferous plants, the pathogen was identified as Colletotrichum higginsianum Sacc. apud Higgins. The optimum temperatures for mycelial growth, conidial germination, and appressorial formation of C. higginsianum isolates PA-01 and PA-19 were at 24-28 ℃. The disease severity increased with increment of temperatures from 20 to 32 ℃ in the growth chamber. The disease severity of Pak-choi anthracnose was more than 80% when the plants were inoculated near 98-100% relative humidity at 28℃for 20 hr. C. higginsianum showed the pathogenicity on the weeds (lindernia antipoda (L.) Aslton) and was able to survive better in soil with pak-choi plant debris. Eight medicinal plant materials were evaluated for their effects on conidial germination and mycelial growth of the pathogen isolates PA-01 and PA-19 on PDA plates. Among those, clove (Eugenia caryophyllata Thunb.) inhibited completely the conidial germination and mycelial growth at the rate of 1% (W/V) whether it was autoclaved or not. In advance, it was proved that clove oil, the major component of clove, was completely effective in inhibiting conidial germination at 750 ppm. Observations under light and scanning electron microscopes indicated that the hyphae swelled and cytoplasma of appressoria leaked out when the fungus was treated with clove oil for 12 hours. The effects of clove water-soluble extract, clove oil, and eugenol were respectively used to control Pak-choi anthracnose. The results showed that clove oil and eugenol were equally effective in reducing more than 50% disease severity compared to clove water-soluble extract. Clove oil was significantly able to reduce more than 75% disease severity of Pak-choi anthracnose at 1500 ppm. In greenhouse tests, clove oil could reduce disease severity of Pak-choi anthracnose when it was sprayed one day in advance of the pathogen inoculation or at the same time as the pathogen was inoculated, but couldn't when it was sprayed one day after the pathogen was inoculated. The effects of clove oil on control of Pak-choi anthracnose were markedly affected when it was mixed with plant nutrients. It was found that KNO3, H3PO3, K2SO4, Ca(NO3)2˙4H2O, and MgSO4 were able to enhance the effect of clove oil on control of the disease.
|Appears in Collections:||植物病理學系|
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