Enhanced biocontrol of tomato bacterial wilt using the combined application of Mitsuaria sp. TWR114 and nonpathogenic Ralstonia sp. TCR112

We previously identified Mitsuaria sp. TWR114 and nonpathogenic Ralstonia sp. TCR112 as potential biocontrol agents to suppress tomato bacterial wilt caused by Ralstonia pseudosolanacearum. Because commercial biocontrol products require a practical cost-effective application method that maximizes their performance, we investigated whether the combined application of TWR114 and TCR112 enhances the biocontrol of bacterial wilt. In pot experiments, all the tested inoculum ratios (i.e., 1:1, 1:2, and 2:1) of the TWR114 + TCR112 treatment significantly suppressed the incidence of bacterial wilt, even at 28 days post-challenge inoculation (dpi) (13–47% wilt incidence), while 60% of plants treated with the individual isolates developed bacterial wilt within 10–12 dpi. The pathogen population in the rhizosphere and aboveground regions decreased considerably after the TWR114 + TCR112 treatment compared with that in the individual treatments. Moreover, the pathogen population in the aboveground parts of TWR114 + TCR112-treated plants had decreased to an undetectable level by 28 dpi. After inoculation with the pathogen, the expression of several tomato defense-related genes was higher in the TWR114 + TCR112-treated plants than in those treated with the individual isolates. Altogether, the results indicate that TWR114 and TCR112 applied together have a synergistic suppressive effect and that stronger defense priming might contribute to the improved biocontrol. The combination of both isolates may be a very promising approach for controlling tomato bacterial wilt in the future.