| Summary: | 碩士 === 國立中興大學 === 植物病理學系 === 89 === A new disease of lettuce, leaf brown spot caused by Acremonium lactucum, has become a serious problem in organic farming in Taiwan during recent years. Disease control experiments were attempted by use of water-soluble extracts of 103 different medicinal plants. Eleven plant materials were effective in inhibiting conidial germination of the pathogen at 1 % (w/v) concentration on the slide culture, and among them seven which including Aster tataricus, Cornus officinalis, Crataegus pinnatifida, Raphanus sativus, Rheum palmatum, Sanguisorba officinalis, and Terminalia chebula, showed complete inhibition at 0.25% (w/v). When these plant extracts were applied respectively together with conidial suspensions (105 spores/ml) of the pathogen onto four-week-old lettuce plants, ones from Raphanus sativus (radish seed meal) and Rheum palmatum showed great efficacy of disease control by reducing the disease severity more than 50%. In this study, radish seed meal was selected as a candidate for the development of botanical pesticide formulation. A preliminary screening of the extracts from various cultivars of radish indicated that cultivars Akamaru Kinmon Hatsuka Daikon (AK-H), Hsia Heng No. 2 (HH-2), and Wan Sheng Ta Mei Hua (WS-T) were superior candidates; the extracts obtained from these cultivars inhibited completely the conidial germination of two pathogen isolates at 0.2% (w/v) concentration. In the laboratory and greenhouse trials, the effect of water-soluble extract from 0.5% (w/v) cv. WS-T radish seed meal on the disease suppression was stable when the extract was sprayed onto lettuce plants three days before inoculation or two days after inoculation. However, the disease severity of lettuce brown spot was significantly reduced when the plants were continuously sprayed three times with the extracts once per week. Seven nitrogen, five phosphate, five potassium, four calcium, three magnesium sources were mixed respectively with water-soluble extract obtained from cv. WS-T radish seed meal and tested for their effectiveness in controlling the disease. NaNO2, K2HPO4, and CH3COOK were effective in increasing the function of the extract on reducing the disease severity. These results indicated that the water-soluble extract of radish seed meal of contained certain unknown components effective in inhibiting the pathogen and thus was of great potential for developing a biocontrol formulation to protect lettuce from the disease. One of the antifungal compounds was isolated from water-soluble extract of radish seed meal with SPE and HPLC. The compound was characterized by the chemical analyses including UV, CI-Mass, 1H and 13C NMR, and IR spectrum. It was confirmed as sulforaphene, which belongs to the isothiocyanate group and derives from glucoraphenin. In future, it is necessary to determine what bio-activity of sulforaphene and other antifungal components in radish seed meal are involved in suppressing the disease development and how to apply the extract for controlling the disease in the fields.
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