非農藥防治十字花科幼苗猝倒病之研究

Abstract

腐霉菌屬病原在全世界可造成多種經濟作物之病害，由於其生長快速，約3-5天即可完成一個世代，且藉由流動水可迅速傳播，感染大面積植株，故常造成嚴重經濟損失。本研究係於田間調查發現十字花科菜園常有大面積缺株或是植株猝倒病徵，經過病原菌分離以及柯霍氏法驗證四分離株之病原性，再輔以型態及分子生物學鑑定後，確認田間主要造成病害之病原為Pythium aphanidermatum以及Pythium deliense。此兩種病菌皆會造成種子無法萌芽，萌芽率由正常的八成下降至一成至三成，對於萌芽後之植株則會導致幼苗鮮重以及乾重之下降，生長不良，嚴重者則莖基部萎縮、倒伏。腐霉菌所危害寄主範圍廣泛，然台灣蔬菜種植中以十字花科所佔據面積最廣，因此本研究將寄主範圍限縮至十字花科作物，並在8種品種對病原感病度之測試中，發現品種間對於病害感受能力有所差異，其中以芥藍為較敏感品種。在生物防治之拮抗實驗中，利用台大植醫實驗室所保存之4種鏈黴菌進行測試，並將鏈黴菌培養在五種天然資材、不同酸鹼值之培養基上了解其拮抗能力的不同，發現Streptomyces BR-br在PDA添加3%黑豆煎汁，pH8環境下可以達到抑制十字花科幼苗猝倒病菌絲生長的最大能力。又在盆栽試驗中發現將Streptomyces BR-br 以浸泡種子的方式施用為最有效預防病害的方式，處理後可以使種子正常萌發，且Streptomyces BR-br具有促進植物生長的能力，使處理後植株之鮮重及乾重皆有增加。由於目前在防治十字花科幼苗猝倒病並無推薦使用的藥劑，故本研究針對目前市面上常用於卵菌的防治藥劑共7種進行篩選，並實際應用於盆栽試驗中，結果較推薦使用除疫寶（80%亞磷酸緩衝液）1500倍稀釋液，每平方公尺澆灌3公升;35%依得利可濕性粉劑，每平方公尺施用2公克藥劑或是使用50%達滅芬可濕性粉劑，每平方公尺施用6公克藥劑。

Pythium sp. cause a lot of important plant diseases around the world. They can complete one generation within 3 to 5 days and can spread over field quickly through water by zoospores, therefore, can make great loss in agriculture. In this study, we conducted field investigation in Taipei area and found that cruciferous damping-off diseases are often seen in Taipei area and frequently causes great loss. After the pathogen isolating and accomplishing the Koch’s postulates, together with the morphologic and molecular identification, Pythium aphanidermatum and Pythium deliense are identified as two major pathogens of the cruciferous damping-off in Taipei area. These two pathogens can attack the seeds, reduce the seed germination rate from normal 80% to 10-30%. The germinated seedlings are also infested and reduce fresh weight and dry weight, moreover damping-off or dead at last. Eight species of cruciferous vegetable were tested for their sensitivity to the pathogen. Results show that different vegetable has different germination rate after inoculated with Pythium aphanidermatum and Pythium deliense disease soil. Among them, Brassica oleracea var. alboglabra is the most sensitive to two pathogens. The biological control study using 4 isolates including: Streptomyces YU01, SCPN, BR-br and BR-bh, preserved by Plant Medical Lab of NTU. Result shows that Streptomyces BR-br reveals the best controlling ability when grown on PDA amended with 3% black bean juice and with pH8. Result also shows that dipping seeds with Streptomyces BR-br spores shows the best efficacy to prevent Pythium aphanidermatum and Pythium deliense damping-off in pot test. Moreover, dipping with Streptomyces BR-br also makes seedlings grow better with greater fresh weight and dry weight. Seven fungicides, which are often used to deal with phytophthora diseases in Taiwan, are screened and tested in this study for their inhibition effects on pathogens. Among them, phosphorous acid solution, etridiazole and dimethomorph are recommened for controlling these damping-off diseases.