Unlocking consortium-induced immunity: Pseudomonas and Microbacterium as biocontrol agents against tomato bacterial canker

Tomato bacterial canker, caused by Clavibacter michiganensis subsp. michiganensis ( Cmm ), poses a significant threat to global tomato production. This study evaluated the biocontrol efficacy of bacterial strains isolated from the rhizosphere and tissues of tomato plants. From 100 isolates screened for antagonistic activity against Cmm , nine exhibited promising inhibitory effects, with strains A23 and C6 showing the highest performance. Molecular identification via 16S rDNA sequencing revealed that these isolates belonged to the genera Pseudomonas , Microbacterium , Alcaligenes , Glutacimibacter , and Providencia . Among them, Pseudomonas sp. A23 and Microbacterium sp. C6 were selected for in planta evaluation, both individually and as a consortium. Greenhouse trials showed that A23 and C6 reduced disease incidence by 38.76 % and 58.90 %, respectively, while their co-inoculation achieved a significant reduction of 78.35 %. In addition to disease suppression, treated plants exhibited markedly decreased vascular browning and canker lesion size, along with enhanced vegetative growth, particularly in shoot and root dry weights. To elucidate the underlying mechanism, qRT-PCR analysis was performed. The results showed that plants treated with the consortium exhibited a significant increase in the expression of key defense-related genes, including PR1 , PR5 , and CHI3 , and a decrease in the expression of PR4 and ACO1 genes, indicating that the consortium enhanced the plant’s systemic defense response. Overall, this study highlights the potential of strains A23 and C6 as effective biocontrol agents and biofertilizers. Their combined application offers a promising and sustainable strategy to manage tomato bacterial canker while promoting plant vigor and resilience. • Nine bacterial isolates inhibited Clavibacter michiganensis growth in vitro. • Strains A23 and C6 reduced tomato canker severity and disease incidence. • A23–C6 consortium suppressed bacterial canker by 78.35 % under greenhouse conditions • Treated plants showed modulated defense gene expression and enhanced biomass.