Abstract: Phage could be used to control plant bacterial diseases, but how to multiply propagate is a key technology. At present, the host bacteria of the bacteriophage are mostly used to reproduce the phage and it could bring risk when the phage is used. In this study, the wild Ralstonia solanacearum strain RSsw326 had been continuously cultivated for 20 generations and a mutant strain with circular colony and a weak motility was obtained. The tobacco was inoculated with the mutant strain by stabbing, injecting and wounding root, and there were no withered symptoms produced on the tobacco. The result proved the strain, named as RSsw326-2, was an avirulent strain. The strain also had no antagonistic effect on other R. solanacearum strains and could be infected by eight phage strains which were isolated from different tobacco-growing areas in Fujian province. Using strain RSsw326-2 as a host to breed the phage, the phage titer could be 10¹⁰ PFU/mL after culturing for 36 h. When tobacco was treated with the culture solution of avirulent strain RSsw326-2+bacteriophage by stabbing, wounding roots and without wounding roots, there were no wilting symptoms on the tobacco in 35 d. But the disease incidence was 100%, 100% and 66.7% in 14 d after inoculation by stabbing, in 28 d by wounding and in 35 d without wounding roots with the culture solution of RSsw326+bacteriophage, respectively. The results also showed that the culture solution of avirulent strain RSsw326-2+bacteriophage performed good control potential against tobacco bacterial wilt disease with 74.1% control efficiency in pot experiment in 21d after treatment. Compared with the treatment by the culture solution of the virulent strain RSsw326+bacteriophage, the symptoms delayed for 8 d. Taking an avirulent strain as host of phage multiple propagation might provide a significant basis for development and preparation of highly effective bacterial phage agent.

Key words: avirulent Ralstonia solanacearum, phage, pathogenicity, biocontrol