| Summary: | 碩士 === 國立中興大學 === 植物病理學系所 === 98 === In the year of 2008, 3 bacterial strains, MBg1, MBg2, and MBg3, were isolated from the decay tissues of king oyster mushrooms that were cultivated at a mushroom farm in Daili, Taichung. The 3 strains elicited decay symptom on king oyster mushrooms and necrosis in tobacco leaves in pathogenicity tests, indicating they might be the causative agents of bacterial decay disease of king oyster mushrooms. The MBg strains were assayed for their physiological and biochemical properties, and the results revealed that they can grow on nutrient agar medium at 41 ℃ but not at 4 ℃, and they are sensitive to the osmotic pressure exerted by 5% (w/v) NaCl. The MBg strains have multiple enzyme activities, including gelatinases, lipases, chitinases, proteases, oxidase, and catalase. The MBg strains were identified using fatty acid methyl ester analysis (Agilent Technologies, Santa Clara, CA) and SHERLOCK® Microbial Identification System, and in each instance, the bacterium was confirmed as Burkholderia gladioli. In addition, the Biolog system (Biolog, Hayward, CA) and sequence identity comparisons of 16S ribosomal DNA gene and 16S-23S internal transcribed spacer (ITS) were performed to characterize the bacteria isolated from king oyster mushroom. The bacteria were also confirmed as B. gladioli based on a similarity of 0.58 with Biolog and 99% sequence identity for 16S rDNA and ITS sequences. Because strains of B. gladioli are commonly found in diverse ecological niches, it is predicted that B. gladioli strains from different environments may have different phenotypic and genotypic characteristics. In this study, we characterized B. gladioli strains isolated from different sources by carbon source utilization, pathogenicity assays, antagonistic activities, ITS sequences, and ERIC/BOX-PCR DNA fingerprinting. Metabolic profiles showed that the MBg strains causing king oyster mushroom bacterial decay are similar to pineapple fruit rot pathogen PBg5 and soil isolate Bg1. ITS sequences and ERIC/BOX-PCR DNA fingerprinting analyses revealed that MBg strains are closely related to soil-isolated strains Bg1 and Bg2 with respective similarities of 97.4% and 0.734. Pathogenicity assays demonstrated that MBg strains and soil-isolated strains Bg1 and Bg2 are virulent to king oyster mushroom and weakly virulent to gladiolus (Gladiolus hybridus) and onions; the strains of pineapple fruit rot pathogen, PBg3 and PBg5, are weakly virulent to king oyster mushroom, gladiolus, and onions; the gladiolus-pathogenic strains HBG4 and HBG10 that were identified as B. glumae are pathogenic to gladiolus and onions but not to king oyster mushroom; the soil-isolated strain Bg3, classified as a member of B. cepacia complex, is weakly virulent to onioin but non-virulent to king oyster mushroom and gladiolus; the soil-isolated strains Bg4 and Bg5 that are also classified as members of B. cepacia complex are not virulent to king oyster mushroom, gladiolus, or onion. In addition, the antagonistic activities of B. gladioli strains were assayed by measuring the mycelium growth of king oyster mushroom and Rhizoctonia solani AG-4 and the bacterial growth of B. glumae RBg9, and the results revealed that all strains of B. gladioli used in this study have inhibitory abilities against the growth of king oyster mushroom, R. solani AG-4, and B. glumae strain RBg9 on cultured media. Taken together, our results indicated that B. gladioli MBg strains isolated from king oyster mushroom share similar phenotypic and genotypic characteristics to soil-isolated B. gladioli strains Bg1 and Bg2.
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