Screening, Separation Of Botanical Inhibitive Compounds Against Rice Sheath Blight And Their Optimalized Conditions For Application

Rice sheath blight, caused by Rhizoctonia solani Kühn, has led to a huge damage on rice planting around the world. Botanical germicides are originated from nature and have great advantages, for example, safety to human beings and animals, nonresistance against themselves caused by pathogens , degradability and friendliness to the environments. Therefore, the development of botanical germicides has become one of popular aspects of agrochemical research.In the present thesis, Pteris multifida, Platycladus orientalis cv.sieboldii and Viburnum awabuki K. Koch were selected from 16 plants for their high inhibitive activities on the growth of R. solani by the method of mycelial radial growth inhibition test. Determination in vitro showed six extraction fractions had resistant efficacy against the sheath blight fungus under greenhouse conditions. Among them, the petroleum ether fraction of P. orientalis and the ethyl acetate fraction of V. awabuki showed better control efficacy, which was achieved at 78.1% and 76.7% to rice sheath blight, respectively, when the applied concentration was 1 mg/mL. The effect was approximate to that of 50% carbendazim WP act, a popular fungicide product.Five compounds, named as Com.1~Com.5, were isolated by the method of column chromatography. Among them, Com.2 and Com.4 exhibited remarkable resistant activities to the growth of R. solani mycelium. Furthermore, the Com.2 and Com.4 were identified as 14-Isopropylpodocarpa-8,11,13-trien-13-ol and (1R,2R,8aS) -Decahydro-1-(3-hydroxy-3-methyl-4-pentenyl)-2,5,5,8a-tetramethyl-2-naphthol, whose local name are totarol and sclareol, respectively, after analysis of MS, 13C-NMR, 1H-NMR, UV-VIS and FT-IR.The results indicate that the control efficacy on rice sheath blight was raised when the crude extractions of P. multifida, P. orientalis and V. awabuki were used together. The extract conditions of active plants have been optimized by single factor experiments. The application conditions of the complexing extracts were optimalized by thorgonal test as follows: complexing extracts at the ratio of 1:1:9 (P. multifida:P. orientalis:V. awabuki, w/w/w) were diluted to 2 mg/mL with water and sprayed on the base of seedlings every 10 days at serious infection situations or every 15~20 days at moderate infection situations. The best control efficacy on rice sheath blight was achieved at about 80%.