Root priming with Bacillus spp. against bacterial wilt disease of tomato caused by Ralstonia solanacearum

Bacillus spp. have long been used as biological control organisms against plant bacterial diseases but the mechanisms by which the bacteria confer protection against the pathogens are not properly understood. Among nine strains of Bacillus spp. three of them, viz. NBAII 63 (B. megaterium), NBAII 71 (B. cereus) and NBAII 65 (B. megaterium) were found highly inhibitory against R. solanacearum. These strains of Bacillus spp. produced indole acetic acid (IAA) and siderophore and solubilized the phosphorous. High amount of IAA (174.2 mu g/ml) and siderophore (1.32 mu g/ml) production followed by the highest phosphorous solubilization (53.3 mu g/ml) by the strain NBAII 63 were found. These three potential Bacillus strains showed the increased activity of defense related enzymes, viz. peroxidase (PO), polyphenoloxidase (PPO), phenylalanine ammonia-lyase (PAL) and total phenols in pre treated tomato plants challenged with R. solanacearum. Significant activities of PO, PPO, PAL were observed at 8 days after the treatment of antagonist and declined gradually afterwards. The maximum phenol content (185 mu g/g of plant tissue) was observed in the tomato plants whose roots were treated with Bacillus strain 63 at 8 days after inoculation treatment. These Bacillus strains could be used as potential biocontrol agent for the management of bacterial wilt disease of tomato.