Rhizobacterium Bacillus amyloliquefaciens Strain SQRT3-Mediated Induced Systemic Resistance Controls Bacterial Wilt of Tomato

Tomato bacterial wilt caused by Ralstonia solanacearum seriously threats tomato growth in tropical and temperate regions around the world. This study reported an antagonistic bacterial strain, Bacillus amyloliquefaciens strain SQRT3, isolated from the rhizosphere soil of tomato plants, which strongly inhibited in vitro growth of pathogenic R. solanacearum. The suppression of tomato bacterial wilt by strain SQRT3 was demonstrated under greenhouse conditions. Additionally, induced systemic resistance (ISR) in tomato as one of the potential disease suppression mechanisms was investigated in the plants inoculated with the isolated bacterial strain SQRT3. The results showed that strain SQRT3 applied with R. solanacearum by drenching significantly reduced tomato bacterial wilt by 68.1% biocontrol efficiency (BE) and suppressed the R. solanacearum populations in the rhizosphere soil compared to the control only drenched with R. solanacearum. The BE of the isolated bacterial strain SQRT3 against tomato wilt increased to 84.1% by root-dipping. Tomato plants treated with both strain SQRT3 and R. solanacearum showed increases in activities of peroxidase and polyphenol oxidase compared with other treatments. The application of strain SQRT3 reduced membrane lipid peroxidation in tomato leaves. The expressions of marker genes for jasmonic acid- and salicylic acid-dependent signaling pathways were faster and stronger in tomato plants treated with both strain SQRT3 and R. solanacearum than in plants treated with either R. solanacearum or strain SQRT3 alone. Collectively, the findings indicated that strain SQRT3 can effectively control tomato wilt.