Abstract
An inoculation test with Ralstonia solanacearum was conducted to evaluate how adding biocontrol agents (BCAs) and lysine or sucrose affects the microbial community structures of tomato roots as well as bacterial wilt of the tomato. In addition, we examined the relationship between the quantity of R. solanacearum DNA and the disease incidence of bacterial wilt. Bacterial and fungal community structures were determined using denaturing gradient gel electrophoresis (DGGE). The addition of BCAs and lysine or sucrose significantly decreased the disease incidence and changed the bacterial DGGE profiles. Canonical correspondence analysis (CCA) indicated that three unique bands observed in lysine treatments were negatively correlated with disease incidence, suggesting that bacterial species corresponding to these bands suppressed the bacterial wilt pathogen. On the other hand, none of the bands in the fungal DGGE profiles were related to disease incidence in the CCA, suggesting that the suppressive effect on bacterial wilt promoted by the lysine treatment was attributed to the bacterial community of tomato roots, not to the fungal community. The quantity of R. solanacearum DNA in the lysine treatment was as small as that in the non-inoculated control, suggesting that the quantity of R. solanacearum DNA in the tomato roots six weeks after sowing might be a useful indicator for assessing the risk of tomato bacterial wilt.
