| Pine wilt disease is one of the most important forest disease in the world .Although it has been researched more than half a century ,its pathogenicity is not clear .At the present time ,most people thought that the bacteria play an important role in the process of wilting ,and the bacteria Bacillus and Poseudomonas have been isolated from the surface of the pine wood nematode .In order to understand fully the species of the bacteria carried by pine wood nematodes and their distribution .We isolated bacteria from the disease wood and studied the identification and pathogenicity of them. The main result were as follows:1. According to the emergence, development, distribution and extention of pine wilt disease in china , the following areas,which were Jiangsu Province , Shanghai city, Guangdong Province , Anhui province ,Hubei province and Zhejiang province etc, were choosed as the typical diseased areas. 58 bacterial strains were isolated from the diseased wood of pinus thunbergii or pinus massoniana which was infected by pine wood nematode in the spring and autumn of 2001, and identified by traditional methods and automatic bacteria identification system. Results showed that there were three dominant genus which belong to Pseudomonas, Pantoeu and Peptostreptococcus , Among those strains, some species of Pseudomonas and Pantoeu existed in different areas, different hosts ,and had wider distribution and higher frequent emergences than others. The results proved that the above-mentioned two species were the most dominant.2. The toxicity of 58 bacterial strains were tested with the bacteria cultural filtered original liquid and concentrated liquid and aseptic black pine seedlings cultured for 60d under the aseptic condition. Results revealed that Pseudomonas, Pantoeu was mainly responsible for rapid wilting of pine trees, among which the activity of parts of Pseudomonas fluroscence, Pantoeu 1 were higher,. While that only a few of Pseudomonas strains and the most Pantoeu were the second, furthermore Peptostreptococcus asaccharolyticus has no wilt activity . the determination comparision between wilting activity of the filtered original and concentrated liquid showed that the active substances produced by bacteria was unstable in high temperature, and the active ingredients could be changed or decomposed to be inactive. The above results were significant in probing the elements of bacterial toxic substances and pathgenic mechanism of bacteria .3. With aseptic black pine seedlings cultured for 4 months and 10 years black pine young trees , the artificial inoculation experiments in doors and outdoors were conductedafter choosing representative bacteria strains. The pathogenesis tests indicated that aseptic seedings and pinus thunberg wilting diseases did not occurred or occurred slowly and lightly as being inoculated with aseptic nematode ,and did not occurred too as being inoculated with bacteria separately,while inoculated with mixed suspension of them ,rapid wilting of pine trees can be caused.When we inoculate the combination of Peptostreptococcus asaccharolyticus and aseptic nematodes , black pine were still safe. Based on the results ,it was suggested that there was certain coorperation between nematode and some species of Pantoeu and Poseudomomas for the disease.4. The reisolation results after inoculation showed that no bacteria was isolated in the healthy black pine inoculated with only bacteria or aseptic pine wood nematode, but a few of nematodes were isolated from the healthy black pine inoculated with only aseptic pine wood nematode. A lot of pine wood nematode and bacterium were isolated from the wilting black pine inoculated with the mixed suspension of aseptic pine wood nematode and bacteria. This suggested only bacteria can not invade successfully.grow and repropagate normally in host, transmit in pine tissues, if no nematode existence. While carried by nematode ,the bacteria can penetrate into pine tissues and develop toxic action normally. On the other hand , the aseptic ne...
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