| Tobacco black shank is the major diseases of tobacco in karst of southwest Guangxi. The normal control methods are using chemical fungicides. The residue of fungicides contaminated environment, harmed to human and livestock, and inducing resistance of plant pathogeny. The biological controls have the advantages of pollution-free, harmless and long-acting. It will be a major technology of disease prevention in future. So in this study, we isolated Phytophthora parasitica var. nicotianae and soil bacteria from karst area in Jingxi county of Guangxi province in which produced high quality tobacco leaves. The antagonistic bacteria were selected by antagonizing action and anti-disease test. Furthermore, for the well antagonizing effect strains, we studied their taxonomy, antagonizing substance, basic fermentation conditions, and the technology of application in field. The results as following:1. A total of 462 strains of bacteria were isolated from 8 soil samples. And 82 of them showed antagonistic effects against P. nicotianae. Results of further screening showed that 16 strains exhibited strong antagonistic action. At last, Integrated the results of diameters of antibacterial circle on soli media and the diseases control for the pot tobacco, 3 bacteria numbered 8-23, 6-70, and 13 were selected for further studied.2. Strain 8-23, 6-70, and 13 were identification based on the results of morphological observation, physiological and biochemical characteristics analyse, and 16S rDNA sequence test. The result showed that strain 8-23 was a near relation species to Bacillus subtil belong to Bacillus spp.. Strain 6-70 possibly was a species of Lysobacter spp., but it need more evidence to testify. And strain 13 was a species of Pseudomonas spp..3. The basic fermentation technics of 3 antagonistic strains were exhibited as follow: (1) Strain 8-23: inoculated 1% (V/V) germs which had been activated for 12 h to 90 ml potato maltose medium (pH 6.0), cultivated in 200 ml triangular flask at 30℃, 180rpm for 24 h. (2) Strain 6-70: inoculated 1% (V/V) germs which had been activated for 12 h to 30 ml potato maltose medium (pH 6.0), cultivated in 200 ml triangular flask at 30℃, 180rpm for 24 h. (3) Strain 13: inoculated 1% (V/V) germs which had been activated for 12 h to 30 ml potato maltose medium (pH 6.0), cultivated in 200 ml triangular flask at 30℃, 240rpm for 24 h.. 4. Anti-disease mechanism and Characteristic of antagonistic substance of the three antagonistic strains: The mechanism of strain 8-23, 6-70, and 13 anti- Phytophthora parasitica var. nicotianae were destroying the structure and function of pathogeny by dissolving their cells wall and / or membrances,. As a result, the ability of anti-disease was exhibited. The basic Characteristic of anti-disease substance was showed as follow: (1) the most part of antibacterial component of strain 8-23 was proteins which were endurable high temperature and sensitive to organic solvent. The crude sediment which sedimentated by (NH4)2SO4 had antagonistic activity. (2) The partial of antibacterial component of strain 6-70 was proteins which were endurable high temperature and sensitive to organic solvent. The crude sediment which sedimentated by (NH4)2SO4 also had antagonistic activity. (3) The antibacterial component of strain 13 was the substance which could not endurable high temperature. Several liposoluble components and the sediment of (NH4)2SO4 had antagonistic activity. It was inferred that the antagonistic substance included liposoluble components and a few high-temperature sensitive proteins... |
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