松萎蔫病病原的研究

Study on the Pathogens of Pine Wilt Disease

为了探讨松萎蔫病与松材线虫的关系,笔者研制了一种简单试验装置"冷闸",使接种的线虫被隔离在松树接种枝内而不能迁移。用该装置进行接种试验的结果表明:在松材线虫被局限于接种枝内而不能移动到寄主其他部位的情况下,接种无菌松材线虫与致病荧光假单胞菌Pseudomonas fluorescens(GcM5-1A),以及该致病细菌体外培养的无细胞滤液,同样能诱发该病。该致病细菌又从接种无菌线虫和致病细菌后病死寄主中分离到并被鉴定,证明符合柯赫法则。致病荧光假单胞菌GcM5-1A体外培养的无细胞滤液接种试验结果说明,该致病菌株培养物中的内吸性毒素导致了寄主的萎蔫和死亡。由此,松萎蔫病经实验证实为首例由细菌和线虫互惠共生复合体引起的植物病害。

Pine wilt disease has become a worldwide threat to pine forests and forest ecosystem. However, its mechanism has not been clearly illustrated, though most scientists working in the area believe that pine wood nematode （PWN） is the only pathogen of the disease. This study indicated the bacteria symbiotically associated with the nematode played an important part in the disease. A series of inoculation experiments were completed with a new developed experimental device, cold valve, by which the nematode and its associated bacteria were confined within the inoculated branch. Here this paper show that the pine wilt disease is a complex disease caused by a complex of PWN and its associated pathogenic bacteria. The results also indicated that without the movement of the two pathogens to other parts of the inoculated pine the axenic PWN the systemic toxins in the culture produced by the pathogenic bacterial strain resulted in wilt and death of the host. Based on the results of the study and reports in the mixed with the pathogenic bacterium, Pseudomonas fluorescens （GcM5-1A） or the cell free culture of the bacterium were able to cause the disease. The bacterium was reisolated from the dead host, inoculated with axenic PWN and the bacterial strain proving Koch＇s postulates. The result＇ from the inoculation of the cell free culture of the bacterial strain in indicated that it was the systemic toxins in the culture produced by the pathogenic bacterial strain that resulted in wilt and death of the host. Based on results of the study and previous reports of the authors on mutualistic symbiosis between PWN and its associated bacteria, the authors pointed out that pine wilt disease is the first experimentally confirmed plant disease induced by a mutualistic symbiotic nematode-bacterial complex.