Construction of Ralstonia solanacearum avirulent mutants and evaluation model of their control efficacy against tomato bacterial wilt disease

Avirulent Ralstonia solanacearum has showed a good potential on control bacterial wilt disease of tomato.In this study,3,12 and 40 avirulent mutants of R.solanacearum were constructed by using spontaneous mutagenesis,60Co-radiated mutagenesis and EZ-Tn5 transponson mutagenesis,respectively.Pathogenicities of these 55mutants were detected with bioassay test using potted tomato in the greenhouse.None of these mutants caused tomato wilting at 15thd after inoculation,which meant that they were all avirulent R.solanacearum.Then,the 55mutants were used to control tomato bacterial wilt and the control efficiencies were compared.The results showed that strain FJAT1458 isolated from tomato plant was the most effective with the control effect of 100%.It was also found that strain FJAT1458 could colonize in rhizospheric soil,root and stem of tomato plant.The colonizing density of FJAT1458 showed a tendency of 'increasing at the beginning and decreasing afterward'during 1- 25 d after inoculation.Meanwhile,higher inoculated concentration and younger seedling age resulted in more colony amount of FJAT1458 in plant.A regression model of control efficiency of the biocontrol agent against tomato bacterial wilt was constructed.When the inoculated concentration of FJAT1458 was bigger,the value of R was less.Therefore,the avirulent mutant FJAT1458 obtained is possessed of good control effect on tomato bacterial wilt.