台灣植物青枯病菌之生態與防治

Abstract

由Pseudomonas solanacearum引起的青枯病是植物最嚴重的細菌性病害之一，在台灣已記載被本病為害的作物計有番茄、煙草、馬鈴薯、甜椒、茄子、落花生、天堂鳥花、草莓、紫蘇、篦麻、胡麻等，最近在蘿蔔、康富利及番荔枝上也被證實有本病的發生。台灣存在的青枯病菌菌株目前已知者都屬於race 1，但其中可分為數種病原型；生化型則屬於biovar 3或biovar 4，極少數菌株為biovar 2。青枯病在夏季或高溫多濕季節發生嚴重，而冬季較少發生。土壤濕度高利於發病，濕度低病害輕微。土壤質地與病害發生無密切關係，但台灣有多處土壤為抑菌土及抑病土。青枯病菌在土壤中的存活受土壤因子的影響，潮濕土壤適合其存活，而乾燥及淹水土壤不利其生存，酸性土壤也較不適宜。如以田間傳播方式造成發病率的不同來分，台灣的青枯病有三種類型。第一類為茄科等大多數植物上的青枯病，主要以土壤傳播式的方法而引起，土壤中病菌的濃度及分佈決定田間的發病率；第二類為草莓上的青枯病，主要經由帶病菌的移植苗傳播而造成，幼苗帶菌率的高低決定田間病害發生的程度；第三類為紫蘇上的青枯病，主要藉著機械傳播式而引起，病菌經採收機械由病株迅速蔓延於大面積的健株上。青枯病有多種可行及正待發展的防治方法，包括抗病育種、抗病根砧嫁接、施用土壤添加物、輪作、生物防治、使用健康種苗、農具消毒及其他耕作措施，但為因應上述傳播方式之不同，施用於某一特定作物上的防治策略之重點應有所差異。 Bacterial wilt caused by Pseudomonas solanacearum is one of the most destructive, widespread bacterial diseases of plants in Taiwan. The disease has been reported to occur on tomato, tobacco, potato, sweet pepper, eggplant, peanut, bird-of-paradise, strawberry, perilla (Perilla crispa), castor bean and sesame. Very recently, the disease has also been observed on radish, comfrey (Symphytum peregrinum) and sugar apple (Annona squarnosa). Strains of P. solanacearum from various hosts tested are all race 1, but several pathovars differ in host range or pathogencity are found among strains. Most strains are biovar 3, some are biovar 4, but a few tobacco strains are biovar 2. Bacterial wilt in many crops is most severe during summer or warm-wet seasons and is much less destructive during winter. The disease occurs in various types of soils, and is favored by high soil temperature and high soil moisture content. However, soils suppressive to P. solanacearum and bacterial wilt of tomato have been detected. P. solanacearurn survives much longer in moist soil than in dry or flooded soil, Low pH soils are less favorable for survival of the pathogen than high pH soils. When the major means of pathogen dissemination which affect the disease severity in fields are considered, three types of bacterial wilt can be recognized in Taiwan. The first type is bacterial wilt occurs on solanaceous and many other plants. The disease on these crops is caused mainly by soil-borne P solanacearurn and the incidence of the disease is determined by the density and distribution of the pathogen in soil. The second type is bacterial wilt on strawberry. The disease is spread mainly by infected seedlings. The wilting symptom during growing stages of strawberry occurs only on those plants grown from infected transplants, therefore, the disease severity in the field is largely determined by the percentage of strawberiy seedlings infected by the pathogen. The third type is bacterial wilt on perilla which is caused by the pathogen transmitted mechanically. Perilla plants rarely become diseased when planted in the infested soil, but wilted easily through stem infection. Young shoots of perilla plants are harvested periodically during the cultivation period by clipping off the top branches of plants with a harvest machine. Because of this practice, the pathogen spread rapidly from diseased plants to heaLthy plants, causing a high incidence of disease. The control of bacterial wilt has been approached in several ways. The control measures available or underdeveloping include breeding for disease resistance, grafting resistant rootstocks, soil amendment, rotation, biological control, use of healthy planting materials, disinfection of contaminated implements and other cultural practices. However, in view of the different means of pathogen dispersal, the control strategy should vary with the particular crop concerned.