Abstract: Biological characteristics of the 60Co-induced mutants of Ralstonia solanacearum to be used as plant vaccines were studied.The avirulent strain of R.solanacearum,FJAT-1458,was treated by 60Co irradiation to create the mutant library.The bio-control efficiency on the bacterial wilt disease and the colonization on the host of the original and the mutated strains were compared.The results showed that the optimum 60Co dosage for the mutagenic treatment was 200Gy.After such treatment,92.5% of the irradiated bacteria were found dead.Among the 52 60Co-irradiated mutants,13.5% of them displayed an increased bio-control efficiency,while 21.6% showed a negative effect,as compared to the original strain.The 15-day,91.7% control efficiency on the bacterial wilt disease of the mutant,FJAT-15022,was the highest among all.It was significantly higher than the original strain,FJAT-1458,which had a control efficiency of 83.3%.Furthermore,the mutant,FJAT-15022,could grow at 40℃,while the original strain,FJAT-1458,could not.The colonization of the 60Co-mutanted strain,FJAT-15022,in the host was 5 days longer than that of the original strain,FJAT-1458.On the other hand,the number of FJAT-1458 in the host was more than that of the mutant,FJAT-15022.