| Summary: | 碩士 === 中興大學 === 植物病理學系所 === 98 === Biocontrol of pathogens, the total or partial destruction of pathogen populations by other organisms, is important to the sustainable agriculture. Soil microorganisms capable of utilizing vegetable tissues for multiplication were isolated and their vegetable liquid cultures were tested for ability of control black leaf spot of mustard cabbage caused by Alternaria brassicicola. A total of 69 actinomycetes, 101 bacteria and 71 fungi were isolated and tested. Among them 1 bacterium and 5 fungi were able to reduce the disease incidence and lesion size of black leaf spot. The liquid cultures of V3F-3 and V5F-13 were inhibitory to conidial germination of A. brassicicola Aba-31. These 2 fungi were identified as Penicillium citrinum and Aspergillus flavus by morphological and molecular methods. Inhibitory substances in the freeze dried powder of liquid cultures of V3F-3 and V5F-13 were most efficiently extracted with methanol and 50% ethanol extract, respectively. The inhibitory substance in P. citrinum V3F-3 culture was fungicidal, and it was completely adsorbed by activated charcoal. The inhibitory substance in A. flavus V5F-13 culture was semi-fungicidal fungicidal, and it was partly adsorbed by activated charcoal. Both inhibitory substances did not have charges on their molecules, and were very stable under high or low pH value. The extracts of P. citrinum V3F-3 and A. flavus V5F-13 were most active at pH 3-4 and pH 3-6, respectively.
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